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CHAPTER XIII DEVELOPMENT OF VASCULAR SYSTEMS

Principal Arteries and Veins.

It was shown at the beginning of this book (pp. 51, 91) that the vase system, in its earliest stages, came into existence as the result of the establishn of connections between networks of channels formed on the yolk-sac, in body-stalk, and in the embryonic body; an extension from the body-stall


Fig. 670. —Scheme of Earliest Circulatory System. (Founded on Eternc

The lower figure is a diagrammatic section to show position of aortae and umbil veins (UV). Am, amnion; N, neural groove; coe, intra-embryonic coelom

the chorion (where similar channels are possibly formed also) puts tl anastomosing systems into relation with the growing villi.

The primitive circulation would seem to be possible through channels est lished in this way at an early stage in embryonic formation; such might represented schematically as in Fig. 670. In this figure it can be seen t

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DEVELOPMENT OF VASCULAR SYSTEMS


1117


ns (vitelline) pass up the wall of the yolk-sac to reach the posterior part of ! embryonic rim, where they join a vein coming from the body-stalk and ming forward to enter the primitive heart-tube. This (C) is a very short )e, doubled in origin, which runs back towards the bucco-pharyngeal area (bp), ing off here two primitive aortcs, which pass back on each side of the area the future membrane, and continue their course caudally to reach the bodylk. As they pass back in the embryo they give off vitelline branches downrds on to the wall of the yolk-sac; later, as the somites form, they will be found give intersegmental branches running dorsally between the somites. When

y reach the chorion they are distributed throughout it and to its villi.

The veins which return the blood in this early circulation must come into stence, of course, with the * arteries,’ and can be said in general terms to



r. 671. — Schemes founded on Conditions in an Embryo of About Twelve Somites, in which the Intra- and Extra-embryonic Ccelomic Cavities are Continuous.

se from the common vascular network as enlargements of its ‘ peripheral ’ t, the ‘ central ’ vessels becoming arterial. Thus veins are found extending the heart along the embryonic rim, which receive the blood returning through body-stalk; these veins (uv), are the umbilical veins, which, passing forward ng the margins of the embryonic plate, reach the anterior end of the heart,e in this margin. The vein is shown in black in the figure, where only the sels of the left side are seen; actually there are two primitive aortae and two bilical veins.

The conditions illustrated in the last figure are those present in the embryo, which there are as yet no somites and no body cavity continuous with the ernal coelom. The result of somite formation, with the reversal of the erior end of the embryonic plate, is shown in the next figure (Fig. 671),





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where the heart is now reversed, and the arterial end points forward, while paired aortae run upwards beside the bucco-pharyngeal membrane and then ti back; intersegmental branches are appearing now. It can be seen now, moreo\ that well-defined vitelline veins are reaching the venous end of the heart (n posterior) by passing up the front of the yolk-sac; the earlier posterior ve have disappeared. The splitting of the embryonic rim by the ccelomic extens leaves the vitelline arteries on the splanchnic wall, but puts the umbilical ve in the somatic wall, close to the continuity of this wall with the amnion; thi: shown in the section in Fig. 671.

The paired aortae lie oh the roof of the primitive pharynx, and receive in t situation ‘ aortic arches ’ from the ventrally placed arterial trunk and vessi but behind the pharynx they fuse into a single vessel, which divides again ii two as it approaches the hinder end; these two umbilical arteries pass into • body-stalk.

Development of Principal Arteries.

The arterial end of the heart opens into a dilated arterial sinus, from wh right and left arteries run into the pharyngeal arches, passing through th to join the right and left dorsal aortee which are lying on the roof of the primit pharynx. All told, there are six of these aortic arches (or pharyngeal artei arches) on each side, but they are never present at any one moment in th totality. They appear from before backward, like the mesodermal arches which they lie. The first is possibly the direct descendant of the primitive ao: of its side, passing dorsally round the bucco-pharyngeal membrane; in any c; it is found very early, before reversal is nearly completed. The second aor arch comes a little later. The third, when it appears, seems to take on the din supply of blood to the dorsal aorta at its anterior end, where this vessel is givi branches to the growing neural (brain) tube, and the first and second arcl break up rapidly and disappear, except for their upper and lower ends for soi little time. The fourth arch appears at about the same time as the third, i fifth is very small and short-lived, like the rudimentary mesodermal arch in whi it lies, and the sixth appears behind this. All these arterial arches, then, appt as vessels running ventro-dorsally within their corresponding pharyngeal arch and conveying blood from the ventrally-placed arterial sinus to the dor aortae for distribution.

The presence of the arterial sinus makes the details of further developmt slightly different in the human embryo from those in lower forms, but t differences are only slight, and the main evolution of the adult pattern frc that of the aortic arches is in line with the generalized vertebrate evolutic Such a generalized conception of the system of aortic arches is that (Fig. 6; given by Rathke many years ago, on which the special variations found amo vertebrates can be worked out. The plan shows the arterial arrangemei flattened out, so that, from the arterial stem, right and left ventral aortce r forward (below the pharynx) and give off at intervals the six aortic arches reach the d or sal aortas (above the pharynx). Small branches pass from i sixth arches into the lungs, evidently the future pulmonary arteries, while f anterior end of each dorsal aorta is carried (beyond the scheme) into the cran cavity as a cerebral artery. It may be added here that eight intersegmen: branches arise from each dorsal aorta, the lowest coming off about oppos or just below the fourth arch on each side; seven of these arteries are cervic but the first is cranial, accompanying the hypoglossal.

Disregarding the gill-bearing vertebrates, we may come at once to 1 Amniota, where the differences in the various phyla are classifiable easily on t scheme. In the first place it is a general rule that the third aortic arch is devot to supplying the brain, while the fourth becomes the main stem for the sup], of the body. Thus the third arch plus the dorsal aorta in front of it becon; the internal carotid, and the fourth arch becomes the ‘ arch 5 of the syster aorta, from which facts it can be assumed that the dorsal aorta between 1 third and fourth arches loses its function, is stretched out, and disappea




DEVELOPMENT OF VASCULAR SYSTEMS


1119


e matter of the two fourth arches, these persist in the reptiles ; the right one 5 the systemic arch in birds, and the left one in mammals. he human conditions are thus shown (Fig. 672) on the scheme as mammalian, first two arches disappear, leaving the ventral aorta opposite them as nal carotid; the third, with the dorsal aorta in front of it, forms the nal carotid; the dorsal aorta behind it, between it and the fourth arch, •pears; the ventral aorta between third and fourth becomes the common id. The original symmetry is disturbed behind this. The fourth left arch s part of the systemic arch, but not the whole of it; the dorsal part of this is formed by dorsal aorta, and the ventral end is the beginning of the ventral

this is represented on the right side by the innominate artery. The right

i arch becomes part of the right subclavian; the whole of the left subclavian he terminal piece of the right subclavian are of intersegmental value. Behind


External Carotid


'ig. 672.—Scheme of the Aortic Arches and their Destination.


e the fifth arches disappear; the left sixth remains as the ductus arteriosus; right sixth disappears except for its ventral end, from which the right lonary artery arises. The common arterial trunk is divided by a septum a dorsal part continuous with the sixth arches, and a ventral part for the ral aortae, and this septum extends towards the heart in a spiral manner, nee the changing relations of pulmonary artery and ascending aorta; this vessel represents the common trunk and its systemic subdivision, binally, right dorsal aorta disappears behind the right fourth arch, so that the rest ie thoracic aorta comes from the fused vessels.

n the human embryo there is no ventral aorta giving origin, as in the scheme, 11 the arterial arches, but if we look at the arterial sinus as having the value hortened ventral aortae conjoined, this difficulty disappears. In any case difference is not of much importance, big. 673 gives, in the uppei row, is showing the changes in the human embryo as seen from the left. The

















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external carotid showing here may be a new formation, but might be some dr< out persisting remnant of the ventral supply to the early anterior arches, the common carotid is either part of the third arch or a drawn-out portion o sinus; it is a very difficult question to decide. The lower figure shows


biG. 673. —Plans to show Changes in Human Embryo: Upper Row f

Left, Lower from Right.

Aortic arches and their remnants numbered in Roman figures.

conditions on the right side; the carotid developments are as on the left, but fourth arch is part of the subclavian, and the dorsal aorta disappears behind

In estimating and following the changes which occur in the art< arches in the neck it must be remembered that the head grows forw leaving structures behind it which were originally ventral to it; th what is really meant when the heart, for example, is said to ‘ desce



Fig. 674.— Plans to show how the Embryonic Relations between Ner and Arteries are exhibited in the Adult Condition.

The growth of the head and elongation of the neck straighten out carotids, while the connection of the fourth arch with the trunk keeps it 1 the heart.

The relationship between the arterial stems (in the pharyngeal arc] and the nerves of the arches is of interest from the point of view of the nor relations in the adult, and also in cases where the adult conditions are unusu






DEVELOPMENT OF VASCULAR SYSTEMS


1121


The nerves of the first four arches lie near the grooves in front of them, and thus in front of the arteries which lie more or less in the middle of the mesomal masses. In the sixth arch, however, possibly because its artery runs k to it and is formed relatively late, the artery lies in front of the nerve. In

ases the nerve, having crossed the dorsal aorta on its lateral side, then turns

ards to gain the visceral surface; thus they all cross obliquely the lines of ir corresponding arteries, but whereas the first four cross in front of their sels, the last crosses behind it. It follows that, when the neck is elongated the vessels drawn out, they are drawn over the nerves of the arches behind m. Thus the internal carotid (third arch) has the superior laryngeal (fourth arch ve) deep to it, while its own nerve, the glosso-pharyngeal, is superficial to it rsal aorta). The fourth aortic arch (arch of aorta and right subclavian) has the irrent laryngeal deep to it, but this nerve on the left turns first round the mentum arteriosum because it crosses behind that artery in the sixth arch.

The fifth arch, with its artery and nerve, is a tiny and transient formation, only brought into description to complete the various systems. Its artery may be as in Fig. 673, or may arise from the arterial sinus and end in one of the neighbouring arches, or even in the dorsal vessel, or may even arise from the proximal part of the sixth artery.

It disappears early and completely.

The right subclavian artery, as shown in the scheme, has its first part formed n the fourth right aortic arch, and its terminal piece from the seventh cervical srsegmental artery. Between these two there is a portion of the right dorsal ta; there is considerable doubt about the limits of these various parts.

There are two well-known varieties of the right subclavian artery of developntal interest. In one the artery arises from the descending thoracic aorta, the other it arises from the left end of the arch of the aorta; in both cases it ses behind the oesophagus to gain the right side. The first of these varieties ms to be an example of persistence of the right dorsal aorta ; the same explanation iometimes given for the second variety, but with much less probability, and would seem to be more probably an example of anastomosis between the two sal aortw. In both cases the fourth aortic arch has evidently disappeared the right side, and as a result the right recurrent nerve turns round the next h in front— i.e., it runs directly downwards to the lower border of the larynx , sing deep to the internal carotid.

Intersegmental Branches : Vertebral Artery. —The first intersegmental artery en by each dorsal aorta accompanies the hypoglossal nerve. After this come en cervical intersegmental vessels. These pass back between the somites, ich they supply, and give branches also to the neural formations lying ernal to these. Since the cranial end of the dorsal aorta is about to be stretched

in the internal carotid, and the next part of it is about to disappear, it is

dent that, if these intersegmental arteries are to continue to supply the uctures mentioned, they must be provided with another artery of origin, e provision is made very early in their history in the form of a longitudinal istomosis connecting them together some little distance from their origins.

An anastomosis of such a sort is a normal occurrence among the intersegmental vessels in the trunk. Usually it remains very small or disappears, but is seen occasionally in the adult, especially in the thoracic region. In the ordinary way, however, it is only in the cervical region that it enlarges and becomes functionally important.

This longitudinal anastomosis ends caudally in the seventh cervical intermental artery. Thus, when the origins from the dorsal aorta fail, the series vessels obtains its blood from this seventh artery. The longitudinally running 'tebral artery is thus made up of these bits of interarterial anastomosis, the ginal intersegmental vessels persisting as its branches. The portion above the as, however, which has a different relation to the issuing nerve, is of another [ue, being the enlarged intersegmental spinal or neural branch.


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The origin of a vertebral artery precedes that of the corresponding subcla 1 artery, so that the subclavian artery is originally a lateral branch of the verte artery. As the development proceeds, however, the subclavian artery incre in size, and greatly exceeds the vertebral artery, the latter vessel being : regarded as a branch of the subclavian.

Origin of Left Vertebral Artery from Aortic Arch. —This, the commo additional branch arising from the arch, is probably an example of the sistence (see Fig. 675) of the sixth intersegmental origin from the dorsal ac with the portion of this aorta remaining as far as the level of the fourth ac arch.

The thoracic and abdominal intersegmental arteries have been refe to already in connection with the aorta.


Fig. 675. —Development of Cervical, Intersegmental, and Vertebra

Arteries, according to Scheme.

The intracranial prolongation of the dorsal aorta on each side is an exan of the enlargement of a neural branch arising from the beginning of this ari and running dorsally into the paraxial tissue round the brain; the dorsal a< itself lies on the upper in-turned ends of the visceral mesoderm of the arc below the layer of paraxial mesoderm. This terminal neural branch en the paraxial layer beside Rathke’s pouch, and, in the adult, pierces the d mater here. Before reaching this, the internal carotid lies on the roof of tubo-tympanic recess, covered by the otic capsule; much later, this cap: extends its ossification partly round it, enclosing it in the carotid canal, bi portion of the artery, still unenclosed, lies in front of this and crosses (as it in the foramen lacerum) the anterior margin of the recess, the auditory tube,

The ramifications of the cerebral arteries are formed in accorda with the growth of the parts of the brain, which is surrounded by a vasci network from a relatively early stage. These vessels are dealt witl part in the section on the central nervous system.



































DEVELOPMENT OF VASCULAR SYSTEMS


1123


•teries of Limbs. —The arteries of the upper limb have been already considered, the lower limb, the accepted views on their development are in large part lptions based on comparative anatomical observations, direct observation » human embryo being an undertaking of great difficulty.

) W er Limb. —At the beginning of the second month the main artery accoms the sciatic nerve, passes deep to the rudiment of the popliteus, and runs

en the primordia of the leg bones to the foot. This ‘ axial ’ vessel is
cted with a small plexus on the extensor aspect of the limb, from which at

ir stage the femoral artery will form. As the femoral channel enlarges, axis ’ vessel sends a secondary branch down superficial to the popliteus, hen degenerates above the level of its connection with the femoral; this dary branch divides to form the tibial arteries, anastomosing with the lal interosseous trunk, which has already given off the anterior tibial, and becomes a small branch of this. The inferior gluteal artery, the popliteal, •art of its middle genicular branch, are remains of the original ‘ axis ' supply,


Fig. 676.— The Venous Trunks of the Septum Transversum of

the Human Embryo (His).

X.X. Upper separated portions of Umbilical Veins R.U.V. Right Umbilical Vein L.U.V. Left Umbilical Vein

V.P. Venous Loops round Gut V.V. Vitelline Veins

the peroneal and perhaps part of the arterial structures in the sole are ed from its interosseous prolongation; the two femoral arteries and the snous branch of the descending genicular artery, when present, are remains e femoral extensor plexus.

Development of the Principal Veins (p. 5 1 ) he primitive veins form two groups. One group returns the blood from the sac and the placenta; and the other group returns the blood from the head neck, anterior limbs, body-wall, mesonephric bodies, and posterior limbs, first group comprises: (1) the vitelline veins, in connection with which the il vein is developed; and (2) the umbilical veins. The second group consists ) the anterior cardinal or primitive jugular veins; (2) the posterior cardinal

and (3) the subcardinal veins; they drain into the veins (or ducts) of

2r on each side. The veins of each group are arranged in pairs, right and


J.V. Primitive Jugular Vein

.V. Cardinal Vein

V.C. Right Duct of Cuvier /.C. Left Duct of Cuvier


























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1124

Sinus Venosus. —This is the venous space made by the confluence of veins of the body; it discharges directly into the common atrium the bloo receives from the veins. It is placed in the septum transversum (pp. 46 and and consists of two ‘ horns,' each of which is made by the junction of the umbili vitelline, and Cuvierian veins of its own side. As described in the developrr of the heart, the right horn is taken up into the right atrium, the left horn becon the coronary sinus. The vitelline veins reach the sinus venosus by rum in the visceral wall to the septum transversum, the others get to the septuir

the body-wall. 1

1. Vitelline Veins and Portal Veins— These veins are developed early, they return the blood from the yolk-sac. They enter the body of the emt along the vitelline duct, and finally open into the sinus venosus after traver the septum transversum. Within the body they ascend parallel with each ot at first in front of, and subsequently on either side of, the duodenal portio the primitive intestinal tube. In the latter region on the caudal side of


Fig. 677. _Schemes to show Formation of Portal Vein from Doi

Connecting Loop between the Right and Left Vitelline Veins.

hepatic bud they become connected by three transverse anastomotic ves two of which lie across the ventral aspect of the gut, and one being placed 0 dorsal aspect. The first or lowest anastomotic vessel lies on the ventral as of the gut; the second or middle vessel is dorsal to the gut; and the tnir highest, like the first or lowest, is ventral to the gut. This is shown m tne

scheme in Fig. 677. , . ,

By means of these three anastomotic vessels two venous rings—lowe caudal, and upper or cephalic—are formed around the duodenal portion oi primitive intestinal tube, these rings constituting the sinus annularis. t their formation the two divisions of the liver-bud are breaking up into ne cylinders, and these are giving off secondary cylinders. Owing to these ne] developments the vitelline veins cease to communicate directly with tne . venosus. The portions of the vitelline veins above the upper duodenal ve ring (shown in Fig. 676 to proceed from its sides) become surrounded hepatic cylinders, and invaded by the secondary cylinders. In this ma




DEVELOPMENT OF VASCULAR SYSTEMS


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portions of the vitelline veins are freely subdivided into blood-channels,

1 are known as sinusoids (Minot). These sinusoids form a network which >ies the meshes of the network formed by the branches of the hepatic cylinders, veins which convey blood from the upper duodenal ring to the hepatic oids are now known as the vence advehentes, and they become the right and \ivisions of the portal vein. The veins which carry the blood from the tic sinusoids to the sinus venosus are known as the vence revehentes, and they ne the hepatic veins.

runk of the Portal Vein. —The portions of the two vitelline veins which id in front of the primitive duodenum lie close together and parallel with other. These portions fuse for a short distance, and form a single venous , which opens into the first, or lowest, ventral anastomotic vessel, or, in ■ words, into the lower part of the lower duodenal venous ring. This short receives the veins of the primitive intestinal tube, and it forms the root e portal vein. The primitive portal vein, therefore, receives its blood from tie yolk-sac, and (2) the primitive intestinal tube within the abdomen. The r ventral anastomosis and the right vein immediately above it quickly

ipear (Fig. 677). . .

is the yolk-sac atrophies the portions of the vitelline veins between it and commencement of the portal vein also atrophy, and the tributaries of the il vein gradually assume their condition in adult life. The vitelline vein, ever, does not disappear for a considerable time, but remains as a free cord ,4) passing out of the umbilicus up to the entrance of the umbilical loop into belly. #

"he following parts of the sinus annularis, or double duodenal ring, undergo phy (see Fig. 677):

1. Right half of lower ventral anastomotic vessel.

2. Right half of lower duodenal ring.

3. Left half of upper duodenal ring.

rhe following parts of the sinus annularis persist:

1. Left half of lower ventral anastomotic vessel.

2. Left half of lower duodenal ring.

3. Middle or dorsal anastomotic vessel.

4. Right upper half of duodenal ring.

5. Upper ventral anastomotic vessel.

These persistent portions, with the exception of the upper ventral anastomotic el, form the greater part of the trunk of the portal vein, the upper ventral stomotic vessel represents a part of the left division of the portal vein.

The portal vein has originally a spiral relation to the duodenal portion of primitive intestinal tube—that is to say, it winds round the left side and sal aspect of the duodenum, and then appears on its right side.

Divisions of the Portal Vein.— These are connected with the upper duodenal ous ring. As previously stated, the veins which convey the blood from this \ to the hepatic sinusoids are known as the vence advehentes, right and lefL.

right division of the portal vein is formed by the right vena advehens, which

ings from the right half of the upper duodenal venous ring, dhe left division firmed by (1) the upper ventral anastomotic vessel, and (2) the left vena ehens

Umbilical Veins.— The two umbilical veins return the blood from the placenta the sinus venosus. They are of small size during the period of the vitelline mlation, but become enlarged as the placenta gradually forms, the two ns unite and form a single trunk within the umbilical cord At the umbi icus 5 trunk enters the body of the embryo, and immediately divides into wo bilical veins, right and left, which traverse the septum transversum and open n the sinus venosus. As they traverse the septum transversum ey are se to the developing liver.


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The left umbilical vein enlarges fairly rapidly, that on the right s atrophying more slowly. Just before the 5 mm. stage the left vein effect capillary junction with the left vitelline vein on the caudal aspect of the sept transversum— i.e., on the caudal or visceral surface of the small liver. 1 connection between the umbilical and vitelline veins of the left side enlar very rapidly, thus making the vessel on the visceral aspect of the liver wt is usually referred to as the ‘ left umbilical vein ’; actually, of course, it is a vite umbilical anastomosis, and the real umbilical vein passes up still beside the lb but dwindles rapidly, and cannot be certainly traced after a fairly short inter When the anastomotic vessel collapses, after birth, it makes the ligament teres of the liver.

In this region part of this fibrous cord lies in the abdominal wall ; part below the liver; the first of these parts is the true umbilical vein, w the second is the vitello-umbilical anastomosis.


Fig. 678. —Scheme to show Early Circulation in Liver, and Direct

of Ductus Venosus.

The right umbilical vein also seems to develop some similar anastom with the vitelline system, but owing to the atrophy of the vein the anastom does not become evident.

The anastomosis of the left umbilical vein with the left vitelline vein oc at the level (in this last vessel) of the upper junctional loop with its fellow, as sh in Fig. 677. As already stated, this upper loop becomes embedded in the lb and forms a part of the left portal vein, whence the fact that the ligamen; teres, buried between two lobes of the liver, runs to join the left division of portal vein.

There is possibly some connection between the entrance of the umbi blood at this level and the disappearance of the original vitelline (A in Fig. 677) between this and the next anastomotic loop, the vol of blood from the larger vein prohibiting entrance of vitelline blood it below.

Ductus Venosus. —Blood from the left umbilical vein enters the live; j increasing amount as the placenta grows, and before long there becomes evil a dilatation into a large vessel of the vascular spaces in the liver lying bet\i the point of entrance of the blood and that of its discharge into the infc







DEVELOPMENT OF VASCULAR SYSTEMS


1127


, cava. This vessel is termed the ductus venosus (or ductus Arantii). It nds from the left portal vein, which has been formed from the uppermost line loop and receives (Fig. 678) the vitello-umbilical anastomotic vessel; ,sses upwards and to the right, reaching the terminal part of the right hepatic nage into the inferior vena cava, which becomes dilated to form its terminal

✓ •

After birth, when the placental circulation has ceased, the ductus venosus becomes a fibrous cord, the ligamentum venosum.


minute portion of the lumen he left umbilical vein remains ious within the ligamentum > of the liver. This pervious ion communicates at the liver . the left division of the portal , and at the umbilicus it is lected with the epigastric veins

he abdominal wall. It thus

is a channel of communication yeen the left division of the al vein and the systemic veins tie anterior abdominal wall. In pervious portion the blood can towards the umbilicus. This stomosis between the portal and emic circulations accounts for enlargement of the veins of the irior abdominal wall in cases of

al obstruction within the liver.

2. The cardinal system of veins iprises several vessels on each

, which ultimately drain their

d into the sinus venosus through right and left veins {or ducts) of ier. A general idea of their ribution can be gained from . 679A. A large vessel, the primijugular or anterior cardinal (or cardinal), drains the cranial part the body, beginning in associa1 with the venous drainage of brain, and passing back through cervical region, where it re/es intersegmental veins, includthe subclavian (S). The posterior dinal runs caudo-cranially, being med in association primarily with mesonephros (W) and receiving srsegmental veins. The posterior 1 anterior cardinal veins join to m the ‘duct of Cuvier,’ situated the septum transversum, cranial the liver ('LL and thus


Fig. 679.—Scheme of Main Venous Drainages of Embryo.

SV, sinus venosus; DC, duct of Cuvier; PJ, anterior cardinal or primitive jugular; C, posterior cardinal; UV and VV, umbilical and vitelline veins.


(L), and thus running ctly into the sinus venosus. # . .

rhe anterior cardinal or primitive jugular veins are two m number—right left—and return the blood from the head, neck, and fore-limbs. Each vein >ists of two parts—intracranial and extracranial. The intracranial part gives , directly and indirectly, to the intracranial sinuses, whilst the extracranial ‘ becomes the internal jugular vein. The intracranial part is known as the



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A MANUAL OF ANATOMY


principal or primary head vein. This vein at its anterior end is on the inner of the trigeminal ganglion; passing backwards from this point, it lies just al the outer part of the tubo-tympanic recess lateral to the facial ganglion and f nerve, and reaches behind this the outer side of the glosso-pharyngeal and va

Its different relations with the several cranial nerve-roots indicate it has been produced from two venous trunks, connected between the rc these trunks are represented in lower vertebrates by the vena capitis late and vena capitis medialis.

At its anterior end the principal head vein receives on each side the anti cerebral veins, a plexiform set of vessels draining the mid-brain, the back ol fore-brain, and the optic outgrowth. The anterior cerebral veins anastoi


Fig. 679A.— To show Main Trunk Veins in Young Embryo.

with their opposite fellows dorsally between the two small cerebral vesic thus forming the rudiment of the superior sagittal sinus, which is elongated the vesicles grow backwards (Fig. 680).

Between the trigeminal and facial ganglia the principal vein receive middle cerebral vein or plexus, draining the front limb of the pontine flex and anastomosing with the anterior veins.

A plexiform posterior cerebral vein opens into the principal head vein betw the facial and glosso-pharyngeal ganglia; it drains the back of the poni flexure and the myelencephalon. These details are shown in Fig. 680, f scheme.

As the cerebral vesicles grow backwards, the anterior plexus becomes n closely connected with the middle set, and its blood is returned by this set







DEVELOPMENT OF VASCULAR SYSTEMS 1129

asing amount. Ultimately the superficial middle cerebral vein, the sphenotal sinus, and the ophthalmic veins, are the only vessels left of the original isive anterior venous plexus. The cavernous sinus is the persisting anterior

>f the principal head vein (second figure).

he middle cerebral vein, however, has in the meantime formed a secondary ’ding channel with the posterior cerebral vein, this channel lying above the capsule and beside the pontine flexure within the developing cranium, the blood which has already been seen to be derived from the anterior 1 into the middle set is carried back through this new channel, and the lal principal vein in its intermediate part gets smaller and disappears, the 1 from its anterior end (cavernous sinus) now passing up the lower portion e original trunk of the middle cerebral vein to reach the new channel, through h it passes to the hinder part of the posterior vein, along which it runs down -enter the hinder part of its old vessel, and thus leaves the cranium with r agus.


680.— Semi-schematic Figures to show Changes in Venous Drainage of Brain (founded on Streeter’s Figures).


Continuing their growth backwards (third figure), the cerebral vesicles carry elongating longitudinal sinus with them, so that it ultimately comes to open

  • th figure) into the posterior set of veins, from the lower part of which the

al sinus is made. The middle cerebral plexus is covered over by the growing des, but is represented in the great cerebral veins and their tributaries, the ar veins being also remnants of their connections with the anterior venous The straight sinus is a new connection (arising on the dorsal side of the -brain flexure when this closes) between the middle and posterior sets of s. The inferior petrosal sinus represents the secondary re-establishment direct connection between the original and persisting anterior and posterior 1 of the primary head vein, but the new channel is within the cranium, and is

a reappearance of the old vein. .

die extracranial part of the anterior cardinal vein, after the obliteration of vena capitis lateralis, commences at the jugular foramen, whence it extends lad, receiving in its course the cervical inter segmental veins. In the vicinity te sinus venosus it meets the posterior cardinal vein of its own side, with which lites. The venous trunk thus formed is called the duct of Cuvier, of which e are two—right and left. These two ducts pass transversely, one on either


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A MANUAL OF ANATOMY


side, to the sinus venosus, into which they open. At this stage the sinus venc also receives the vitelline and umbilical veins of each side. The ducts of Cu are in the septum transversum (see pp. 46 and 52).

As the heart descends from the region of the fore-gut, the ducts of Cu become vertical, and are in line with the anterior cardinal veins. When sinus venosus becomes merged into the right atrium, and the heart undergo^ slight rotation from right to left, the left duct of Cuvier is placed dorsal to left atrium before opening into the right atrium.

Each anterior cardinal vein is joined, near its caudal extremity, by corresponding subclavian vein.

Close to the junction the subclavian vein receives the external jugular V This vein is a secondary formation, and is probably derived from a poste auricular vein, being subsequently reinforced by a pre-auricular vein.


F IG . 681.— The Venous Plexus lying between the Two Primitive.Jugui

JUST BEGINNING TO FORM THE LEFT INNOMINATE CONNECTION (19 MM.)

A transverse anastomotic vessel is now formed, called the transverse jug vein. It is developed (Fig. 681) in the ventral plexus connecting the primitive jugulars. It extends from the junction of the left anterior cardinal left subclavian veins to the right anterior cardinal vein at a point a little b< the place where it receives the right subclavian vein. This transverse jug vein, which extends obliquely from left to right, with a downward inclmal gives rise to the left innominate vein. The venous blood from (i) the left of the head and neck and (2) the left fore-limb now passes through the innominate vein into the permanent superior vena cava. The right innomi vein is formed by the short portion of the right anterior cardinal vein w intervenes between the place where it receives the right subclavian vein and place where the transverse jugular vein joins it. The portion of the right ante cardinal vein, which lies immediately below the place where the transverse jug vein joins it, forms the upper or extra-pericardial part of the permanent sup( vena cava —that is to say, the part above the point where the vena azygos o] into it. The lower or intrapericardial part of the superior vena cava is develc






DEVELOPMENT OF VASCULAR SYSTEMS


n 3 J


. the right duct of Cuvier. The permanent superior vena cava therefore isents (i) the lower part of the right anterior cardinal vein, and (2) the

duct of Cuvier.

'he portion of the left anterior cardinal vein immediately below the left unity of the transverse jugular vein forms the upper part of the left superior costal vein, thus accounting for the ending of that vein in the left innominate which, as stated, is formed by the transverse jugular vein.

'he left duct of Cuvier undergoes partial obliteration. Its terminal part, l with the left lateral cornu of the sinus venosus, gives rise to the coronary 5. The portion next the terminal part also persists in the form of a very ite vein, called the oblique vein of left atrium, which lies over the posterior ct of the left auricle. The obliterated portion is represented by the vestigial


bo. 682. — Sectional Plans to illustrate Venous Modifications in Cardinal Systems in the Middle Region of the Abdomen.


of left atrium, which is a small triangular fold of the serous pericardium in t of the root of the left lung.

‘osterior Cardinal Veins. —These are two in number—right and left—and return the blood from the mesonephroi, body-wall, and hind-limbs. They >n either side of the aorta dorsal to the mesonephroi. The caudal end of vein receives the inferior gluteal vein, which is the primitive vein of the -limb. A little above this point it is joined at a later period by the external vein, which has now been developed.

die cephalic end of each posterior cardinal vein joins the corresponding nor cardinal vein, and the trunk so formed is the duct of Cuvier.

Amongst other tributaries, the posterior cardinal veins receive intersegmental s, such as the lumbar and intercostal veins, and veins from the intermediate mass.







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A MANUAL OF ANATOMY


The posterior cardinal veins lie on the dorsal side of the mesonephroi, cardinal veins run longitudinally on the inner and ventral sides of the mesonep within which the cardinals and subcardinals are connected by anastomt veins; they run into the cardinals at the two ends of the bodies. A third sy: of veins develops on the dorsal side of the cardinal on each side, forming a pi round the groups of sympathetic ganglion cells as these grow down from posterior root ganglia. As this ‘ periganglionic ’ system enlarges with the gn and extension of the nervous masses, it forms an extensive plexus, joi laterally with the inter segmental veins , ventrally with the cardinal, and wit) subcardinal internal to this. In many animal forms this venous system constil a definite supracardinal vein on each side, with retro-aortic anastomoses, but a development is not found in the human subject, and retro-aortic conned are few and far between; hence it seems convenient to use the term ganglionic as representing the human condition or modification of the supracarc formations.

Progressing with the ganglionic and nervous growth, the perigangli plexus extends forwards and inwards on each side as a juxta-aortic plexi veins, and from this a pre-aortic plexus is quickly formed. The pre-ai extension is seen in the thorax, and is very marked in the abdomen belov level of the superior mesenteric artery; between these two parts the growt the suprarenal and its association with the sympathetic and the formatio the diaphragmatic crura seem to interfere with the formation of the pre-ai plexus. The part of the left renal vein that lies in front of the aorta is made 1 this plexus below the superior mesenteric artery, putting the two subcard] in connection owing to the extensive anastomoses between these and the gny supracardinal vessels. Caudally, the aorta divides into two umbilical arte and the supracardinal plexus is carried down on each side dorsal to these arte extensions from this plexus here on the sacrum appear to be the origin of left common iliac vein in this part.

The sectional plans shown in Fig. 682 will be of use probably in enabling reader to follow the complicated changes going on in these different sets of ves In I are shown the two mesonephric formations in section, beside the mei mesentery. On the left an intersegmental vein (in) is seen opening into posterior cardinal (C), which is situated on the dorsal and lateral side of mesonephros, and is joined by a plexus within that body with the subcarc (SC) in the medial part of the body near the base of the mesentery. On the r side is shown a stage a very little later, in which a plexus of minute veins is surrounding the sympathetic neuroblasts which have descended from the ne crest; this ‘ periganglionic ' plexus is connected with the intersegmental \ and also (although this is not shown) actually with the posterior cardinal, plexus, following the extension of the neuroblasts, shows a rapid ventral extern as seen in II, towards the ventral aspect of the aorta, over which (III) it pa and joins with the plexus of the other side. It is to be noted that this exten is correlated with a marked anastomosis with the subcardinal, as seen in III, in the same figure is shown the evident tendency of the intersegmental vei: transfer its drainage to the plexus—that is, in general terminology, to trar it to the supracardinal vessels. The connection with the subcardinals ii marked that the transaortic plexus appears very soon to be intersubcardi as is suggested in III, and becomes intersubcardinal in actuality before (IV), as the original anastomosis with the plexus begins to atrophy or break This break is favoured by the establishment of longitudinal anastomoses betv the successive ‘ plexus ' units, so that their blood is now carried cranially longitudinally running and definite supracardinal vessel, which only communic with the subcardinals here and there. In the meantime the intersegme veins have come to drain altogether via the ‘ plexus ’ into this longitud vessel, and the posterior cardinal (in this abdominal region) disappears (c) f the scene. These changes are shown in IV. The last figure (V) is a schem illustrate the age-changes described above. The intersegmental veins in f younger stages (below) are joined by a plexus with the subcardinal (SC), bu



DEVELOPMENT OF VASCULAR SYSTEMS


1133


become older (higher) they establish a longitudinal drainage of their own lose their connections with the subcardinal, except, for example, where the renal vein is made.

'he changes just described are of the nature of general changes; their modificai and extensions, as shown in the development of the inferior vena cava azygos systems, remain for description.

humming up these matters from the viewpoint of the respective cardinal it may be said that the posterior cardinal is formed on each side in association the mesonephros, which it drains, and also receives intersegmental veins, he mesonephros degenerates the cardinal vein gets smaller, and disappears pletely in the abdomen. Its intersegmental tributaries have previously . transferred to the supracardinal (periganglionic) system. Changes in the ax will be dealt with later.

die subcardinal is an accessory channel in the inner part of the mesonephros, extent corresponds with this body, and it joins the main cardinal at its smities. It is connected with this vein by a venous plexus throughout its se, and also secondarily with the supracardinal system and its derivatives; of these last is the left renal vein in front of the aorta, which in this way mes practically an intersubcardinal connection.

rhe supracardinal system is not developed so completely in man as in most le other mammals; its early state constitutes a ‘ periganglionic ’ system, but term, it must be understood, is only a descriptive word applicable to the human yo, and indicates its supracardinal arrangements. The veins of this system lorsal to those described above, with which they are connected by free .tomosis. They take over secondarily the intersegmental drainage, allowing posterior cardinals to disappear, and they develop a longitudinal drainageel of their own, so that their contained blood is not (or is only in part) carried the subcardinal; at the upper end, however, this longitudinal vessel opens the subcardinal, as will be seen when treating of the thoracic vessels, rhe compound systems of cardinal veins, as shortly described above, are metrically placed on the right and left sides, in the abdominal and (future) acic parts of the embryo. The development of the suprarenal glands, of liver, and of the diaphragmatic structures altogether breaks the continuity le systems, which can now be said to have thoracic and abdominal developts only indirectly connected. The abdominal development is concerned he formation of the inferior vena cava and its associated vessels, while the

  • os and left superior intercostal systems are produced from the thoracic

dopments; these vessels, therefore, can be considered at once.


Development of the Inferior Vena Cava.

The inferior vena cava, as regards its development, consists of two divisions >wer or postrenal, and upper or prerenal.

These descriptive names are given to the two parts because it is at the level of the left renal vein, which has been seen to be practically intersubcardinal, that the developmental values of the parts of the vein .change ; the ‘ renal' term, therefore, applies to the venous level, and not necessarily to the kidney itself.

Below the level of the left renal vein, the inferior vena cava is formed from the it longitudinal vessel of the supracardinal system, which receives the intermental (lower lumbar) veins of the right side; a similar formation is found ■he left side. The posterior cardinals disappear when the intersegmental veins their terminations, and the subcardinals also atrophy, as the mesonephros ins to move down, only retaining the drainage of the gonad at this level; s the supracardinal alone is left to carry on the drainage of the body-wall, Further changes usually occur on the left side, where the longitudinal vessel supplanted by a deeper longitudinal channel connecting the intersegmental


H34


A MANUAL OF ANATOMY


veins on the transverse processes, deep to the psoas. Thus the more superb vessel disappears; but it occasionally persists as a left inferior vena cava, extend up to the left renal vein (see Fig. 684).

Sometimes the retro-aortic anastomosis, which is a feature of the suf cardinal system in other forms, may make a partial appearance in the hun individual, when one or more lower left lumbar veins will pass behind aorta to empty into the inferior vena cava.

Above the level of the left renal vein the subcardinals on each side lie in fr of the suprarenal glands, round the outer sides of which the posterior cardii course cranially. Before long the right subcardinal establishes a commumcat


Fig. 683.— Cardinal and Subcardinal Veins, etc.

(Frederick T. Lewis, in the American Journal of Anatomy.)

with the veins (hepatic) emerging from the dorsal aspect of the liver; this C( munication is situated in the right-hand part of the common dorsal mesentf This junction, enlarging steadily, provides a new and direct channel by which blood in the right subcardinal can reach the heart, and the left renal, ahead) position, affords a means by which that from the left subcardinal can ' advantage also of the new channel. Thus the prerenal portion of the inte. vena cava is of subcardinal origin from the entrance of the left renal vein to relation with the suprarenal gland, where it receives the suprarenal vein.. Ab this it is formed by the hepatic anastomosis and the common hepatic vein, wi

The supracardinal system-which empties itself fundamentally (w. possible) into the subcardinal—forms the lower part of the main vein, but as s





DEVELOPMENT OF VASCULAR SYSTEMS


ii35


ssible— i.e., where the subcardinal persists—opens into it. Thus the cony of the great vein is effected.

le kidneys, growing cranially, lie among the veins of the supracardinal n, and drain into them. Thus the right renal vein is altogether supra ml in value, and joins the longitudinal supracardinal vessel as this reaches bcardinal ending, thus a very little below the level of the left vein. The snal vein, at its renal end, is of the same value as the whole of the right vein,

s transaortic portion is not represented on the right side; it passes through


Fig. 684. —Schemes to show 1 Formation of Inferior Vena Cava.


ardinals (Sub) are plain; supracardinals (Sup) black; posterior cardinals are not shown, as they are not concerned in the formation.

In A the supracardinal system is establishing its longitudinal vessel on ?ach side, and so communicates with subcardinal. Subcardinals pass aeyond suprarenals (dotted ovals) and there is no connection with the aepatic veins (H). They are joined by a transaortic (dotted) junction, and receive veins (G, G) from the gonads.

In B the supracardinal no longer communicates with subcardinal, except it R; here the renal vein is placed on each side. Subcardinals accordingly iegenerate below entrance of gonad veins. Right subcardinal has now diected a junction with hepatic veins behind liver.

In C any upper continuation of subcardinal above suprarenal is cut off 3 y diaphragm. Final values of parts of I.V.C. are apparent. The ascending supracardinal (X) on left is replaced by the deeper (Y). The junctional part )f left common iliac is an intersupracardinal (periganglionic) formation.


tion of the subcardinal, where this remnant exists to receive the left supraand left spermatic or ovarian veins.

he right and left veins of the gonad drain from the beginning into the 'rdinals, and thus, in the adult, reach the renal level because there is no ordinal remaining below this.

he left suprarenal vein is probably a remnant of the left subcardinal, correcting with the part of the vena cava formed by the subcardinal above the level; the current of blood in it, however, is reversed.

he posterior cardinal vein, having lost its intersegmental branches, disappears the abdomen by the middle of the second month, having taken no part in 'rrnation of the inferior vena cava.













1136


A MANUAL OF ANATOMY


Thoracic Cardinal Formations.

The prolongation of the three cardinal systems into the thorax from abdomen is interrupted first by the rapid enlargement of the suprarenal gla This particularly affects the subcardinals, but these glands still, for a little i discharge some of their blood by small veins into the thoracic parts of the cardinals; soon, however, the extension of the diaphragm, over and be them, cuts them off finally from this way of discharge and leaves them onl) abdominal subcardinals for drainage.

The terminal piece of the posterior cardinal remains on both sides, persisting portion is the part above the entrance of the subcardinal, exten



Fig. 685.— Schemes of Cardinal Systems in the Thorax.

On each side upper part of posterior cardinal (PC) persists. Longituc supracardinal (Sup), connected at first with subcardinal (Sub), only ret ultimately its terminal opening into this; thus this extreme terminal f of subcardinal persists, the rest of subcardinal and of postcardinal appearing below this point. On left side the original symmetry is fur broken up, and retro-aortic junctions cross to right supracardinal.

A is early condition, B the final state. VC, duct of Cuvier; PJ, primi jugular or anterior cardinal.

from this to the duct of Cuvier. The extreme terminal bit of the subcard also persists, joining the posterior cardinal; immediately below this tern section the longitudinal supracardinal vessel joins the subcardinal, and the of the subcardinal disappears. This junction of the two veins corresponds r or less with the entrance of the sixth thoracic intersegmental vein into the of the supracardinal longitudinal vein. These details will be followed r easily, perhaps, with the aid of the diagrams in Fig. 685.

On the right the azygos vein is formed, below the sixth intercostal level, 1 supracardinal elements; at this level a very short ring of subcardinal come and above this it is persistent posterior cardinal.

On the left the conditions are at first symmetrical and similar, but as the innominate vein forms and the intersupracardinal junctions appear behind





DEVELOPMENT OF VASCULAR SYSTEMS


ii37


, the system is broken in variable ways. The termination of the posterior tal is in the left superior intercostal vein, but the terminal piece of this is true jugular (anterior cardinal). The lower hemiazygos is always supralal.

Development of the Lymphatic System.

ie lymphatic system consists of lymphatic vessels and lymphatic glands des. There is also lymphoid or adenoid tissue, as in the thymus body, tioid follicles and villi of the intestinal mucous membrane, lymphatic es of the spleen, palatine tonsils, and pharyngeal tonsil. There are two 5 in the development of the lymphatic system—primary and secondary. irimary stage is concerned in the formation of lymph-sacs, and the secondary consists in the formation of lymphatic vessels and lymph-glands. fmph-Sacs. —There are two pair of lymph-sacs and two single sacs, as vs:

1. Jugular (2).

2. Retro-peritoneal (1).

3. Cisterna chyli (1).

4. Posterior (2).

pinions differ as to the development of these lymph-sacs. The view of nee R. Sabin will be stated first. According to this lady the sacs are oped as sproutings from the endothelial lining of veins, and this constitutes rimary stage in the development of the lymphatic system, lgular Sacs. —The jugular lymph-sacs, right and left, are the first to appear, is situated on the outer side of the lower part of the primitive anterior nal vein, which becomes the internal jugular vein. It is formed from part capillary venous plexus, connected in early life with the anterior cardinal A large part of this plexus disappears, whilst the connection of the inder with the anterior cardinal vein is severed. There thus results a died collection of capillaries, lined with endothelium and in close proximity e outer side of the lower part of the anterior cardinal vein. These capillaries ne dilated, and subsequently join to form the jugular lymph-sac of each side, h is lined with endothelium, and which establishes a fresh connection with ower part of the anterior cardinal vein, where it is joined by the subclavian a valve being formed at the venous junction by a protrusion of part ie lymph-sac at the place of junction. The jugular sac of each side is ected externally with peripheral lymphatic vessels which extend to the , neck, and fore-limb bud of the same side. The caudal end of the left sac mes connected with the thoracic duct, whilst the caudal end of the right becomes connected with the right lymphatic duct. The dorsal part of sac becomes converted into a plexus of lymphatic vessels, from which is of lymph-glands are developed.

tetro-peritoneal Sac. —The retro-peritoneal or pre-aortic lymph-sac is single, is formed from a capillary venous plexus in the root of the mesentery, which ns is connected with the great pre-aortic transverse anastomotic vessel which nds between the two subcardinal veins. The capillary plexus in the root tie mesentery becomes converted into a lymph-sac, without any venous tection, and this constitutes the retro-peritoneal sac, which establishes a munication with the cisterna chyli, and through it with the thoracic duct, ultimately replaced by a plexus of lymphatic vessels, and from this plexus ns of lymphatic glands are developed which lie along the ventral aspect of abdominal aorta. From the retro-peritoneal sac lymphatic vessels pass in the mesentery along the branches of the superior mesenteric artery, and e form another lymphatic plexus, from which the mesenteric lymphatic leal) glands are developed. Subsequently lymphatic (lacteal) vessels enter wall of the small intestine.

’osterior Sacs. —The sciatic lymph-sacs, right and left, are developed from llary venous plexuses in connection with the two primitive iliac veins. On

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A MANUAL OF ANATOMY


1138

either side the sac extends from near the caudal end of the cisterna chyli alo the outer side of the primitive iliac vein. It ultimately becomes convert into lymphatic glands.

Cisterna Chyli .—The cisterna or receptaculum chyli is a single sac, situat at the caudal end of the thoracic duct. It is developed from, and replaces venous plexus. The thoracic duct connects the cisterna chyli with the 1 jugular lymph-sac, and the cisterna chyli communicates with each poster sac. From each jugular sac a vessel grows caudalwards. On the right si this vessel constitutes the right lymphatic trunk, and on the left side it forms 1 thoracic duct. As the thoracic duct approaches the developing aortic arch divides and gives rise to two thoracic ducts, which embrace that arch and th pass to join separately the cisterna chyli opposite the mesonephroi. Subsequen these two ducts fuse, and one duct is formed.

The thoracic duct is developed from a series of venous capillaries, origina having a connection with veins.

Lymphatic Vessels. —The formation of these vessels, along with that ymph-glands, constitutes the second stage in the development of the lympha


Afferent Lymphatics


Fig. 686.—Diagrammatic Section of Lymphatic Gland (Sharpey, fr

Quain).

system. According to Sabin, the lymphatic vessels are formed from the en thelial lining of the lymph-sacs, whilst the lymph-glands are. developed ft plexuses of lymphatic capillaries. The development of the thoracic duct, as stat takes place from several groups of venous capillaries. It is the largest lympha vessel, and it connects the cisterna chyli with the left jugular sac.

The lymphatics derived from the jugular lymph-sacs pass to the head, ne and fore-limb buds; those from the posterior lymph sacs extend to the hi] limb buds; and those from the retro-peritoneal (mesenteric) lymph-sac en the mesentery, within which lymph-glands (mesenteric) are developed connection with them. From these mesenteric glands, in succession, m lymphatic vessels pass to the intestinal tube.

The other view of the development of the lymphatic system, held by Hu ington amongst others, is that the connection of the lymphatic vessels with venous system is secondary\ and not primary, as Sabin holds. According this other view the lymphatic vessels spring from lymph-spaces, which are forn in the mesoderm (mesenchyme), and are lined with mesothelium. The endothe cells of the lymphatic vessels are derived from this mesothelium, and not fr









DEVELOPMENT OF VASCULAR SYSTEMS


ii39


lous endothelium, according to Sabin, and the vessels establish a connection le venous system at a later period.

nph-Glands. —Some of these are formed in connection with the lymphdiilst others are formed in connection with peripheral lymphatic vessels, are three stages in the development of a lymph-gland. The first stage s in the formation of a plexus of lymphatic capillaries pervaded by con;-tissue septa. The second stage consists in the invasion of these septa od-capillaries, surrounded by lymphocytes. The third stage consists in mation of a lymph-sinus from the original plexus of lymphatic capillaries.

3 essential elements of a lymph-gland are thus threefold—namely: (1) a of lymph-capillaries; (2) blood-capillaries, surrounded by lymphocytes, connective-tissue septa; and (3) a lymph-sinus.

h lymph-gland is connected with several lymphatic vessels. 1 hose which
he gland are known as afferent vessels, and they open into the peripheral

deal part of the lymph-sinus. Those which emerge from the gland are L efferent vessels, and they arise in the central or medullary part of the -sinus. In no case does a lymphatic vessel pass uninterruptedly through >h-gland. The gland is a station in the path of a lymphatic vessel, which 3nts the terminus of that vessel, but not the terminus of the lymph. That after leaving the afferent vessel, flows in succession through the cortical edullary parts of the lymph-sinus, and from the medullary part it flows re efferent vessels. It is, therefore, so far as the lymph is concerned, a f, so to speak, changing carriages at a glandular station. During this s any injurious matter is taken up by the branched cells (phagocytes) of nph-sinus, and the lymph is furnished with a contingent of lymphocytes.

Structure of Lymphatic Vessels.

lymphatic vessel, of large size, consists of three coats-—inner, middle, iter. The internal coat {tunica intima) consists of a longitudinal network stic fibres lined with endothelial cells. The middle coat {tunica media) ts of plain muscular and elastic tissues disposed for the most part transy. The external coat {tunica externa) consists of (1) longitudinal bundles of

tive tissue, and (2) plain muscular and elastic fibres, disposed for the

part longitudinally, lined with endothelium.

mphatic vessels are furnished with bloodvessels and nerves. Most ol are also provided with valves, similar to those of the veins. Each valve ts of two semilunar segments, facing one another, which are foldings of the coat, containing connective and elastic tissues. They project slightly ds each other, and their free edges are directed in the course of the lymfih1. The valves are situated at short intervals, and they serve to prevent of lymph. When a lymphatic vessel becomes distended it presents a d appearance, with constrictions between the projections, these constrictions ponding to the attached margins of the valvular segments, svelopment. —According to Sabin, the lymphatic vessels are developed from Ldothelial lining of the primitive lymph-sacs (see Development of Lymphatic m).

Structure of Lymphatic Glands.

lymphatic gland consists of a capsule, which encloses the glandular sube. The capsule is composed of connective tissue, containing elastic fibres.

ie glandular substance presents two parts—superficial or cortical, and

al or medullary. Each of these parts is permeated by a supporting frarneof trabeculae derived from the capsule. Ihese trabeculae are composed o active tissue, with a few plain muscular fibres. They subdivide the cortex follicles, between which they form incomplete septa. In the medulla the

culae are arranged in a reticular manner. .. ,

be glandular substance is formed by lymphoid or adenoid tissue, wnic sts of retiform tissue, with lymphocytes in its meshes. In the cortex o


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A MANUAL OF ANATOMY


the gland this lymphoid tissue is disposed as lymph-follicles, and in the m it forms lymph-cords. In both parts of the gland there are spaces betwe< glandular substance and the supporting trabecular framework. These s which are for the passage of lymph, constitute the lymph-sinus. This si broken up at all parts of the gland by retiform tissue, the meshes of whi partially lined with branched cells of the nature of phagocytes. The glai substance, except the lymph-sinus, is permeated by blood-capillaries.

Lymphatic glands are furnished with bloodvessels, nerves, and lym vessels. The arterioles pass to the glandular substance, being at first enshe by the supporting trabeculae of connective tissue, and subsequently by the re tissue of the glandular substance. The nerves are destined for the plain mu tissue of the trabeculae and bloodvessels.

The lymphatic vessels are of two kinds—afferent and efferent. The a vessels enter the gland over its surface, whilst the efferent vessels emerge definite part of the gland, where there is a slight depression, called the t The afferent vessels convey lymph to the cortical part of the lymph-sinus, the efferent vessels convey lymph from the medullary part of that sinus, much as the medullary part of the gland extends quite to the surface at the where the depression, known as the hilum, exists, the efferent vessels e from the gland through this hilum, which also gives passage to the arterie veins.

Development. —Lymphatic glands are developed partly from the prii lymph-sacs and partly from peripheral lymphatic vessels (see Developm* Lymphatic System).


CHAPTER XIV

THE HEAD AND NECK


BACK OF THE SCALP AND NECK.

andmarks. —The external occipital protuberance can, as a rule, be

out readily enough in the male, and the superior nuchal line,

ill developed, may be felt extending outwards from it. The oid process of the temporal bone can be distinguished without ulty behind the auricle. The occipital artery, with the greater iital nerve on its inner side, lies about inches to the outer side e external occipital protuberance. The occipital lymphatic gland, [ands, may be felt, when enlarged, over the upper part of the izius or semispinalis capitis muscle. The spine of the seventh cal vertebra, or vertebra prominens, can easily be felt, and that le sixth may also be made out. Extending from the external )ital protuberance to the seventh cervical spine there is an elonI depression, called the nuchal furrow, which indicates the position tie ligamentum nuchse. It is possible to feel the strong bifid 3 of the axis by sinking the finger deeply into the upper part of luchal furrow near the occipital bone, but the spines of the third, Hi, and fifth cervical vertebrae lie too deeply for detection. Lymic glands may be felt, when enlarged, along the posterior border le sterno-mastoid muscle.

Jack and Side of the Neck—Fasciae. —The superhcial fascia presents ing worthy of note. The deep fascia closely invests the cervical ion of the trapezius, and is then prolonged over the posterior lgle of the neck to the posterior border of the sterno-mastoid, re it divides to ensheathe that muscle. It will be described in lection with the deep cervical fascia.

Jutaneous Nerves. —The nerves of this region are as follows: the )Ccipital; the greater occipital; the third occipital; the medial iches of the posterior primary rami of the third, fourth, and fifth ical spinal nerves; the lesser occipital; the great auricular; the rior cutaneous nerve of neck; and the descending superficial iches of the cervical plexus—namely, the supraclavicular nerves Fig. 687).

Die suboccipital nerve is the posterior primary ramus of the first ical nerve; it only occasionally supplies the skin on the outer of the greater occipital area.

Fhe greater occipital nerve is the medial branch of the posterior lary ramus of the second cervical nerve. It pierces the upper

1141


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A MANUAL OF ANATOMY


part of the semispinalis capitis muscle, and sometimes the trape2 about -J inch from the middle line. It then runs upwards, with inclination outwards, and accompanies the occipital artery to the era integument, lying on the inner side of that vessel. Its branches long, and have an extensive distribution, reaching as far as the vei of the skull. Laterally it communicates with the small occif nerve, and medially with the third occipital.

The third occipital nerve is a small offset from the me branch of the posterior primary ramus of the third cervical ne Having pierced the trapezius, it ascends medial to the gre; occipital nerve, with which it communicates, and has a lim distribution to the occipital integument inside that nerve.

The medial bran< of the posterior prin rami of the third, fou and fifth cervical ne; appear through trapezius close to middle line, and t outwards to supply skin of the back of neck, that of the tl furnishing, as j stated, the third c pital nerve.

The lesser occij nerve is one of the cending superfw branches of the cerv plexus, and arises fi the anterior prim ramus of the sec cervical nerve, so times receiving a bra from that of the third. It appears at the posterior border of the stei mastoid muscle, and ascends along that border to the occipital reg Here it divides into mastoid and occipital branches, which supply skin of the mastoid, outer part of the occipital, and adjacent porl of the parietal regions. It furnishes an auricular branch to the 5 of the upper part of the inner surface of the auricle, and it commi cates with the greater occipital, the posterior branch of the gi auricular, and the posterior auricular branch of the facial, lesser occipital nerve is sometimes double, and in these cases one port of it usually pierces the anterior border of the trapezius.

The great auricular nerve, like the lesser occipital, is one of ascending superficial branches of the cervical plexus, and arises two roots from the anterior primary rami of the second and tl cervical nerves. It turns round the posterior border of the stei


Occ. Front.

G. Occ. N. Third Occ. N. Less. Occ. N.


Fig. 687.—To show the Nerves and Vessels on the Back of Scalp and Neck.












THE HEAD AND-NECK


ii 43


istoid immediately below the lesser occipital nerve, and passes wards and forwards upon that muscle towards the lobule of the ricle, on approaching which it divides into anterior and posterior anches. The posterior branch is distributed to the skin over the istoid region, the skin of the inner surface of the auricle, and sends e or two twigs through the cartilage of the auricle to the skin covery the lower part of the outer surface; and the anterior branch is dis

Auricularis Anterior


Auricularis Superior


Auricularis Posterior


Occipital Belly of Occipito-frontalis

Greater Occipital Nerve Semispinalis Capitis Lesser Occipital Nerve

Splenius Capitis


Levator Scapulae

Great Auricular Nerve

Accessory Nerv e anches from Third and Fourth Cervical Nerves to Trapezius Scalenus Medius


Lateral Supraclavicular Nerve


Trapezius


' Frontal Belly of Occipitofrontalis


Orbicularis Oculi

Levator Labii Superioris Alaeque Nasi

Levator Labii Superioris - Zygomaticus Minor Zygomaticus Major

Masseter Orbicularis Oris Depressor Labii Inferioris _ Depressor Anguli Oris Mentalis

Anterior Belly of Digastric Stemo-hyoid

Superior Belly of Omo-hyoid Sterno-mastoid

Anterior Cutaneous Nerve of the Neck

— Medial Supraclavicular Nerve

— Intermediate Supraclavicular Nerve


Scalenus Anterior

»

Inferior Belly of Omo-hyoid Subclavian Artery (third part)

Fig. 688.—The Right Side of the Head and Neck. The platysma has been removed, and the nerves are shown.


ibuted to the skin over the parotid gland and angle of the jaw. The )sterior branch communicates with the lesser occipital and posterior lricular nerves, and the anterior branch communicates in the parotid and with the facial nerve.

The anterior cutaneous nerve of the neck (transverse cervical irve), like the lesser occipital and great auricular, is a superficial 'anch of the cervical plexus, and arises by two roots from the anterioi










ii 4 4


A MANUAL OF ANATOMY


primary rami of the second and third or third and fourth cervic nerves. It appears at the posterior border of the sterno-mastc close below the great auricular, and turns over that muscle deep the external jugular vein to reach the front of the neck, where it w be afterwards described.

The supraclavicular nerves from the cervical plexus appear at t posterior border of the sterno-mastoid below the accessory, usua] as a single trunk which arises by two roots from the anterior prima rami of the third and fourth cervical nerves or from the fourth alor This trunk, as it descends, divides into three branches—name] medial, intermediate, and lateral —which pass downwards over t clavicle, and will be afterwards referred to.

Deeper Structures.

Ligamentum Nuchse. —This is a strong fibrous band which occupi the median line of the neck. Its superficial fibres are attached superior to the external occipital protuberance, and interiorly to the spi of the seventh cervical vertebra. Its deep fibres are attached the external occipital crest, and to the spines of cervical vertebr from the second to the sixth inclusive. They also extend into t interspinous intervals between the interspinales muscles, where th represent interspinous ligaments.

Muscles—Cervical Portion of the Trapezius — Origin. —fi) T inner third of the superior nuchal line of the occipital bone, and t] external occipital protuberance; and (2) the ligamentum nuchse.

Insertion. —(1) The posterior border of the outer third of ti clavicle; and (2) the inner border of the acromion process of t] scapula.

Nerve-supply. — (1) The accessory nerve (spinal root); ai (2) branches from the cervical plexus, which are derived from t] anterior primary rami of the third and fourth cervical nerves. T] nerves enter the deep surface of the muscle after passing benea its anterior border a little above the clavicle, and they here for a plexiform communication with each other.

Blood-supply .—The superficial branch (superficial cervical arter of the transverse cervical artery ramifies on and gives branches the deep surface of the muscle.

The fibres are directed downwards, forwards, and outwards.

This part of the muscle lies on the semispinalis capitis just belo the occiput, and below this on the splenius and levator scapuke; tl superficial branch of the transverse cervical artery and superfici branch of the ramus descendens (arteria princeps cervicis) of tl occipital artery anastomose deep to it, and its nerves enter it. As approaches its insertion its fibres lie over the supraspinatus, a fati pad being interposed.

Action .—The cervical fibres, acting from their origin, elevate tl outer end of the clavicle and the point of the shoulder. Acting froi


Fig. 689. —Dissection to show Muscles on Back of Neck.

Insertion and Posterior Border of the Sterno-mastoid.—This muscle nserted into (1) the outer surface of the mastoid process of the poral bone, and (2) the superior nuchal line of the occipital bone r about its outer half, or more. The posterior border of the $cle forms the anterior boundary of the posterior triangle of the k, and has the following nerves related to it: (1) the lesser occipital snds along it to the head; (2) the great auricular passes upwards


THE HEAD AND NECK


1145


r insertion they extend the head, and incline the neck towards same side, the face being directed towards the opposite side.

The anterior border of the muscle forms the posterior boundary he posterior triangle of the neck.

)ccasionally a small muscle, called the transversus nuchse, is met with, nding from the external occipital protuberance to the tendon of insertion le sterno-mastoid. It may be fleshy or tendinous.


Cut. Muscles Longiss. Cap. Semispin. Cap.


Splenius Cerv. Levator Scap.


Semisp. Cap. Sterno-mastoid Splenius Cap.












1146


A MANUAL OF ANATOMY


and forwards superficial to it towards the lobule of the auricle; (3) anterior cutaneous nerve of the neck crosses it in a forward directi (4) the accessory appears from behind it, along with the branc of the third and fourth cervical nerves to the trapezius; and (5) supraclavicular branches of the cervical plexus emerge from unt neath it.

Some deep cervical lymph glands are situated along the poste border of the sterno-mastoid muscle. They will be described h (see p. 1199).

The levator scapulae, rhomboids, serratus posticus super splenius, semispinalis capitis, longissimus cervicis, longissimus cap: semispinalis cervicis, intertransversales, and interspinales muscles be found described in connection with the muscles of the back 1 p. 400 et seq.).

Second and Third Parts of the Occipital Artery. —At the mast process this vessel lies very deeply. Having crossed the rectus cap lateralis muscle, it enters the occipital groove on the inner aspeci the mastoid process, where it is covered by the following structu in order from the surface inwards: (1) sterno-mastoid; (2) spier capitis; (3) longissimus capitis; (4) mastoid process; and (5) posterior belly of the digastric. In its backward course the ve rests in succession upon the insertions of the obliquus capitis supe and semispinalis capitis, and it escapes from beneath the musi covering it in the following order: posterior belly of the digast longissimus capitis, splenius capitis, and sterno-mastoid. A emerging from beneath the last-named muscle, it lies for a little the posterior angle close to the apex, and then, frequently pierc the occipital origin of the trapezius, it enters upon the third pari its course. This part ascends along with the greater occipital ne to the occipital region, where it divides into several long tortu branches (Figs. 690 and 691).

Branches. —The branches of the second and third parts are follows: mastoid, meningeal, descending, communicating, muscu and occipital. The mastoid branch passes through the mast foramen when there is one on the outer surface of the mastoid proc and supplies the diploe and mastoid air-cells, as well as the adjac dura mater. The meningeal branches enter the cranial cavity throi the jugular foramen, and take part in the supply of the dura me of the posterior fossa. The descending branch (arteria princeps cervi< arises under cover of the splenius capitis, and at the outer bor of the semispinalis capitis it divides into a superficial and deep brar The superficial branch is distributed to the splenius capitis and trapez and anastomoses in the latter muscle with the superficial brand the transverse cervical artery. The deep branch passes deep to semispinalis capitis, and anastomoses upon the semispinalis cerv. with (1) the deep cervical artery, a branch of the costo-cervical tm and (2) branches of the vertebral artery. The communicating branc enter the suboccipital triangle, where they anastomose with branc


THE HEAD AND NECK


1147


the vertebral artery. The muscular branches supply the contiguous iscles. The occipital branches, which are the terminal branches,

at first two in number, but these soon divide into several long

tuous branches, which supply the occipital belly of the occipitontalis and the integument as high as the vertex. They anastomose


g. 690. — To show Course of Occipital Artery (OA) as a Dotted Line on

the Under Side of Skull.

passes deep to mastoid process and muscles attached to this (digastric, longissimus capitis, sterno-mastoid, and splenius). It is lateral to rectus lateralis (RL), rectus major (R.Mj), superior oblique (SO), and semispinalis capitis (SSC). It emerges between splenius and trapezius (T).

th one another, with the posterior auricular, the posterior branch the superficial temporal, and their fellows of the opposite side.

The occipital venous plexus communicates with the posterior iricular and the posterior branch of the superficial temporal veins, receives the parietal emissary vein, which emerges through the





1148


A MANUAL OF ANATOMY


parietal foramen, and so a communication is established with t] superior sagittal sinus; a communication is also formed with tl sigmoid sinus by means of the mastoid emissary vein through tl mastoid foramen. Sometimes it receives a small occipital emissa\ vein which emerges through an opening at the external occipit protuberance, and then a communication would be established wii the confluence of the sinuses.

Two or three occipital veins leave the occipital plexus. Tl external vessel is known as the posterior external jugular vein. Havii

been reinforced by tributaries from the superficial structures at tl upper part of the back of the neck, the posterior external jugular ve passes on to the sterno-mastoid, where it opens into the extern jugular. The middle occipital vein (inconstant) accompanies tl occipital artery, and usually opens into the internal jugular. Tl internal occipital vein, having in some cases pierced the trapeziu passes beneath the semispinalis capitis, and enters the suboccipit triangle. In this situation it joins the suboccipital plexus, from whi( the deep cervical and vertebral veins emerge.

Occipital Lymph Glands. —These glands are usually two in numbe and he superficial to the occipital portion of the trapezius, or the upp part of the semispinalis capitis. They receive their afferent lymphati from the back part of the scalp, and their efferent lymphatics pass the deep cervical glands.

Deep Cervical Artery. —This vessel is in most cases a branch of tl costo-cervical trunk of the second part of the subclavian. Havii passed backwards between the transverse process of the seveni cervical vertebra and the neck of the first rib, it ascends upon tl semispinalis cervicis, under cover of the semispinalis capitis, towar< the level of the spine of the axis, where it anastomoses with the de( branch of the ramus descendens of the occipital. In its course furnishes a spinal branch, which enters the vertebral canal throu^ the intervertebral foramen for the eighth cervical nerve, and mu cular branches, which anastomose with branches of the vertebr artery.

The deep cervical vein begins within the suboccipital triangle the suboccipital plexus, which receives the internal occipital vei It descends in company with the deep cervical artery to the low' part of the neck, where it passes forwards between the transver: process of the seventh cervical vertebra and the neck of the first ri and ends by joining the vertebral vein just before that vessel terminate in the innominate vein.

In addition to the muscular branches of the occipital and dee cervical arteries, the deep muscles of the back of the neck receh twigs from the second part of the vertebral artery, which travers* the foramina transversaria of the upper six cervical vertebrae. The: twigs pass backwards through the intertransverse spaces, and anas! mose with branches of the ramus descendens of the occipital artei and the deep cervical artery.



THE HEAD AND NECK


1149


Suboccipital Region—Muscles—Rectus Capitis Posterior Major

Origin .—The ridge leading to one of the tubercles in which the ne of the axis ends.

Insertion .—The outer part of the inferior nuchal line of the occipital ne, and the subjacent area.


Nerve-supply .—The posterior primary ramus of the suboccipital rve.

The direction of the fibres is upwards and outwards, in spite of its ime.

Action. —(1) To rotate the face towards the same side; and (2) to tend the head.






















A MANUAL OF ANATOMY


1150

The muscle is pyramidal, and its insertion is largely covered the obliquus capitis superior.

Rectus Capitis Posterior Minor— Origin.— The posterior arch the atlas close to the tubercle.

Insertion. —The inner third of the inferior nuchal line of the occipi bone, and the subjacent area as low as the foramen magnum.

Nerve-supply .—The posterior primary ramus of the suboccipi nerve.

The direction of the fibres is upwards in an expanded manner.

Action. —To extend the head.

The muscle is fan-shaped, and lies deeper than, and medial the rectus capitis posterior major.

Obliquus Capitis Inferior — Origin.- —The outer and upper aspect the spine of the axis.

Insertion. —The lower surface of the transveise process of the at at its back part.

Nerve-supply. —The posterior primary ramus of the suboccipi nerve.

The direction of the fibres is outwards and slightfy upwards.

Action .—To rotate the atlas along with the head, so that the fa looks towards the same side.

The muscle is thick and fleshy. At its origin it is interpos between the rectus capitis posterior major superiorly and the high bundle of the semispinalis cervicis interiorly. The greater occipi nerve winds round its lower border.

Obliquus Capitis Superior — Origin. —The upper surface of the trai verse process of the atlas at its back part.

Insertion .—The occipital bone between the outer parts of i superior and inferior nuchal lines.

Nerve-supply. —The posterior primary ramus of the suboccipi nerve.

The direction of the fibres is upwards and very slightly inwards.

Action .—(1) To extend the head, and (2) to act as a slight late flexor of the head.

The muscle is triangular.

Suboccipital Triangle. —This triangle is situated under cover of 1 upper part of the semispinalis capitis close below the occipital bone.

Boundaries — Supero-medial. —The rectus capitis posterior maj External. —The obliquus capitis superior. Inferior. —The obliqi capitis inferior. The roof is formed by the semispinalis capitis a longissimus capitis, and the floor by half of the posterior arch the atlas and half of the posterior atlanto-occipital membrane. * contents are (1) the third part of the vertebral artery, (2) the si occipital plexus of veins, and (3) the posterior primary ramus of first cervical nerve. The greater occipital nerve turns upwards rou the inferior oblique and crosses the inner part of the triangle deep the semispinalis capitis, and the deep division of the ramus descend* of tde occipital artery runs down near this.


THE HEAD AND NECK


1151


lird Part of the Vertebral Artery. —The vertebral artery, having i through the foramen transversarium of the atlas, enters upon bird part of its course, and takes a winding course backwards


Recti Capitis Posteriores Minores


Rectus Capitis Posterior Major


Tubercle on Posterior Arch of Atlas


Spine of Axis-

Interspinales


,Suboccipital Triangle


Obliquus Capitis Superior


’-.Mastoid Process


Vertebral Artery (Third Part)

Posterior Primary Ramus of Suboccipital Nerve ' Transverse Process of -- Atlas

* Obliquus Capitis Inferior Greater Occipital Nerve


Semispinalis Cervicis (upper two bundles)


Fig. 692.—The Suboccipital Triangle.


inwards. It lies in the vertebrarterial groove of the atlas, the

rior primary ramus of the first cervical nerve being beneath it,

it passes under an arched band of the posterior atlanto-occipital


693.—Atlas seen from Above, to show Position of Vertebral Artery

and Suboccipital Nerve.

hrane, which is sometimes ossified. It thus leaves the suboccipital igle, pierces the dura mater, and enters the cranial cavity through oramen magnum. The third part of the vessel furnishes muscular






1152


A MANUAL OF ANATOMY


branches to the adjacent muscles, which anastomose with the rai descendens of the occipital and the deep cervical of the costo-cerv trunk.

Suboccipital Plexus of Veins. —This plexus is formed by bram which proceed from (i) the vertebral venous plexuses, (2) the adjat muscles, and (3) the occipital periosteum. It receives the inte: occipital vein, and the blood is conveyed away from it by the d cervical vein, already described, and the vertebral vein, which wil afterwards considered.

Posterior Primary Division of the First Cervical or Suboccii Nerve. —This division passes backwards as a single nerve in the ve brarterial groove of the atlas, lying between the bone and the tl part of the vertebral artery. On entering the suboccipital triangl divides into branches which supply the obliqui, recti posteriores, semispinalis capitis muscles. A filament joins the greater occip nerve.

Posterior Primary Rami of the Cervical Spinal Nerves.—

cervical nerves are eight in number, the first being known as the s occipital nerve. Each breaks up into an anterior and a poste primary ramus. The posterior primary ramus of the first or s occipital is single, and has just been described. The posterior prim rami of the lower six arise in the intervertebral foramina, and e soon divides into a lateral and medial branch. The upper two cerv nerves make their exit behind the articular masses, and their poste primary rami cross the vertebral arches behind these; the second div: into medial and lateral branches. The lateral branches of all are tributed to the deep muscles, and do not become cutaneous. medial branch of the posterior primary ramus of the second, whic of large size, constitutes the greater occipital nerve. It winds nr the lower border of the obliquus capitis inferior, and pierces semispinalis capitis, to which it gives branches. Later it r pierce the trapezius to reach its cutaneous distribution, which been already described. The medial branches of the third, fou: and fifth are directed inwards superficially to the semispin cervicis, to which, as well as to the semispinalis capitis, they { branches. Close to the cervical spines they pass backwards me^ to the spinalis capitis (biventer cervicis), and, having pierced splenius and trapezius, they reach the integument, which they sup] The medial branch of the posterior primary ramus of the third, be] piercing the trapezius, gives off a small ascending branch, knowr the third occipital. It passes upwards, lying at first under cove: the trapezius, and then passing through it to reach the occipital inte ment. The medial branches of the posterior primary rami of sixth, seventh, and eighth are directed inwards towards the cerv spines beneath the semispinalis cervicis, and are distributed to adjacent muscles. They do not furnish any branches to the inte ment.



THE HEAD AND NECK


ii53


The Scalp and Temporal Region.

ascise. —The place of the deep fascia beneath the skin may be to be taken by the epicranial aponeurosis of the occipito-frontalis

le. The aponeurosis becomes thin and fascial over the temporal

ns. Where it is thick and aponeurotic it is firmly attached to overlying skin by fibrous processes, between which are small r lobules, so that the subcutaneous laver is firm and somewhat ular in appearance. The vessels and nerves are distributed in this

  • , which loses its fibrous nature in the temporal regions and becomes

lerficial soft fatty layer.

uperficial Nerves and Vessels. —The superficial nerves of the ero-lateral aspect; the greater, small, and third occipital nerves; the mastoid branch of the great auricular , have been described idy. In the fronto-parietal region two sensory nerves are met —namely, the supra-orbital and supratrochlear —both of which lerived from the frontal nerve, which is one of the branches of the

halmic division of the fifth cranial nerve. In the temporal region

the temporal branches of the facial nerve , the auriculo-temporal


1 n

u 6 Uf.

  • Y «r


Skull


Fig. 694.—Diagram of Section through Scalp.


e, and the zygomatico-temporal nerve. Of the arteries of the p, the third part of the occipital artery, in the posterior region, has 1 described. Those of the fronto-parietal region are three in ber—namely, the supra-orbital , supratrochlear , and anterior branch he superficial temporal. The superficial temporal artery ramifies he side of the head in the temporal region.

Qie supra-orbital nerve, which is of large size, leaves the orbit •ugh the supra-orbital foramen. It then ascends, lying at first ) to the upper part of the orbicularis oculi and the frontal belly he occipito-frontalis muscle, but subsequently piercing the latter cle in two branches, medial and lateral. The lateral branch is the er of the two, and its offsets extend as far back as the lambdoid ire. As the supra-orbital nerve passes through the supra-orbital 'h it furnishes one or two twigs to the mucous membrane of the tal sinus and to the diploe of the frontal bone, and after leaving notch it sends downwards branches to the integument of the upper id. After this the nerve supplies the integument of the frontoetal region.

rhe medial and lateral branches of the supra-orbital nerves sometimes leave orbit separately, and each may form a notch or foramen of its own.








A MANUAL OF ANATOMY


1154

The supratrochlear nerve, which is of small size, is medial to supra-orbital nerve. It leaves the orbit close to the medial angi process of the frontal bone, where it lies above the pulley of the s-upe oblique muscle of the eyeball. It then ascends deep to the upper j of the orbicularis oculi and the frontal belly of the occipito-front muscle, and, piercing the former muscle, it has a limited distribui to the frontal integument close to the median line. As the nt leaves the orbit it furnishes twigs to the inner part of the integurr of the upper eyelid.

The supra-orbital artery is a branch of the ophthalmic, and emei from the orbit with the supra-orbital nerve. It is distributed to structures covering the frontal bone, and anastomoses with the su] trochlear branch of the ophthalmic artery and the anterior brand the superficial temporal artery. In the supra-orbital notch it fumis one or two branches to the mucous membrane of the frontal sinus to the diploe of the bone, and after leaving the notch it sends do wards branches to the integument of the upper eyelid (Fig. 698).

The supra-orbital vein passes downwards and inwards to a p( just above the medial angle of the orbit, where it joins the suj trochlear vein. In this manner the angular vein is formed, whic the commencement of the anterior facial vein. The supra-orbital ^ receives tributaries from the frontal region and the upper eyelid, ; in the region of the medial angle of the orbit it communicates with superior ophthalmic vein. It also communicates with the supe ophthalmic vein through the supra-orbital notch, and this commun tion receives the frontal diploic vein, which returns the blood from diploe of the frontal bone and mucous membrane of the frontal sir

The supratrochlear artery (frontal artery), like the supra-orbita a branch of the ophthalmic, and leaves the orbit with the supratroch. nerve. It is distributed to the structures over the frontal bone me* to the supra-orbital artery, with which it anastomoses, as well as v its fellow of the opposite side.

The supratrochlear vein (frontal vein), of large size, passes do wards near the median line, and at a point just above the medial ar of the orbit is joined by the supra-orbital vein, the resultant ve being the angular vein. At the root of the nose it communicates v its fellow of the opposite side by a transverse vessel, called the m arch.

The supra-orbital and supratrochlear veins communicate with e other, and with the tributaries of the anterior branch of the superfi temporal vein.

Occipito-frontalis. —This muscle consists of the following pa (1) two occipital bellies, (2) two frontal bellies, and (3) the epicra aponeurosis.

Each occipital belly arises from (1) the highest nuchal line of occipital bone; and (2) the outer surface of the mastoid process of 1 temporal bone immediately above the insertion of the sterno-mas muscle.



THE HEAD AND NECK


ii55


Insertion .—The epicranial aponeurosis.

Each belly forms a thin, broad sheet, the length of the fasciculi Lg about ij inches. The two bellies, right and left, are separated ards the median line by a portion of the epicranial aponeurosis, ch here dips down between them.

Each frontal belly, right and left, is separated superiorly by a row angular portion, of the epicranial aponeurosis, but interiorly / are in contact. Origin .—(1) The subcutaneous tissue of the


Fig. 695.—To show Occipital Belly of Occipito-frontalis.

)row and root of the nose, where the fibres blend with the upper - of the orbicularis oculi and the corrugator supercilii; and (2) slightly 1 the zygomatic process of the frontal bone, and from the nasal

e.

Insertion ,—The epicranial aponeurosis a little below the level of fronto-parietal suture.

Hie fasciculi are about 3^ inches long, and the innermost fibres riorly are regarded by some as being prolonged downwards upon nasal bone as the procerus muscle.





A MANUAL OF ANATOMY


1156

Epicranial Aponeurosis. —This is the intermediate tendon of occipito-frontalis muscle. It forms an aponeurotic stratum ben< the superficial fascia, and is connected firmly to the skin by fib processes, which separate the subcutaneous tissue into lobules, deep surface is loosely connected by areolar tissue to the subja* periosteum. Posteriorly it gives insertion to the two occipital be and in the interval between these it dips down to be attached to inner part of the superior nuchal line of the occipital bone and external occipital protuberance. Anteriorly it gives insertion to two frontal bellies. Laterally, below the superior temporal : it is prolonged downwards over the temporal fascia as a deh


Fig. 696. —Shows Frontal Portion of Occipito-frontalis.

expansion, which gives origin to the auricularis superior and auricul anterior muscles. It is connected to the superior temporal line I thickening of the loose areolar tissue between it and the bone.

Nerve-supply .—Each occipital belly is supplied by the poste auricular branch of the facial nerve, and each frontal belly is supp by the temporal branches of the facial nerve.

Action .—The two occipital bellies draw backwards the epicra aponeurosis, and along with it the scalp. The two frontal bellies from above, elevating the eyebrows, and throwing the skin of frontal region into transverse wrinkles. When the occipital and fro' bellies act simultaneously the scalp is drawn backwards, and eyebrows are forcibly raised. In certain cases the frontal bellies 1









THE HEAD AND NECK


ii57


n the reverse direction, their lower attachment being fixed by other muscles, such as the orbicularis oculi, corrugator supercilii, and crus. When this is done the scalp may be alternately twitched r ard and backward, a simian habit which may be acquired by

tice.

Pericranium. —This is the periosteum of the cranium, and it is sly connected by areolar tissue to the superjacent epicranial leurosis.


Parotid Duct. Buccinator Muscle_

Facial Artery Submental Artery

Lingual Artery Sup. Lar. Art. and Nerve Thyro-hyoid Muscle Superior Thyroid Artery


Inf. Belly of Omo-hyoid

Subclavian Artery (third part)


Transverse Facial Artery


Superficial Temporal Artery

- Maxillary Artery


Posterior Auricular Artery


Occipital Artery


-Stylo-hyoid Muscle


-Post. Belly of Digastric

-Hypoglossal Nerve

-Nervus Descendens

Cervicalis External Carotid Artery


Stemo-mastoid — Trapezius


_Transverse Cervical Artery

-.Suprascapular Artery


Fig. 697. —The Left Side of the Head and Neck. The platysma has been removed.


The temporal branches of the facial nerve pass upwards a little in tt of the auricle, and supply the following muscles: the frontal Y of occipito-frontalis, upper part of the orbicularis oculi, corrusupercilii, auricularis superior and auricularis anterior. They municate with the auriculo-temporal, zygomatico-temporal, and 'a-orbital nerves.

Hie auriculo-temporal nerve is a branch of the mandibular nerve, 'h is the third division of the fifth cranial nerve. It emerges just nd the capsule of the mandibular joint, turns upwards round the of the zygoma, and ascends immediately in front of the auricle in









A MANUAL OF ANATOMY


1158

company with the superficial temporal artery, lying between that, ves and the auricle

Branches.—In this part of its course the nerve furnishes following branches! (1) two branches to the external auditory meat which enter the canal between its osseous and cartilaginous walls, a supply the integument of the meatus, the upper of the two branc. giving an offset to the tympanic membrane; (2) two auricular brand which supply the skin of the tragus and outer aspect of the auri over less than its upper half; and (3) superficial temporal brand which supply the integument above and in front of the auricle, and the temporal region generally.

The zygomatico-temporal nerve (temporal branch of temporo-ma nerve) from the maxillary is of small size, and pierces the tempc fascia about 1 inch above the anterior part of the zygoma, and cl behind the frontal process of the zygomatic bone. Having cc municated with one of the temporal branches of the facial nerve has a limited distribution to the integument of the anterior part the temporal region.

The superficial temporal artery is one of the terminal branches the external carotid artery, from which it arises within the pare gland on a level with the neck of the mandible. Leaving the gla it ascends in front of the auricle in company with the auriculo-tempc nerve, which lies between the vessel and the auricle, and after a cou of about 2 inches it divides into its two terminal branches.

Branches.—These are as follows: (1) transverse facial; (2) articul (3) auricular; (4) middle temporal; (5) zygomatic; and (6) termina namely, anterior and posterior.

The transverse facial artery will be described in connection w the face. It arises within the parotid gland, and in its course furnis glandular branches. The articular branches supply the mandiby joint. The auricular branches supply the outer aspect of the auri' and in part the external auditory meatus. The middle tempc artery pierces the temporal fascia immediately above the zygoma, c then ascends in a groove on the outer surface of the squamous p of the temporal bone deep to the temporalis. It gives branches to temporalis, and anastomoses with the deep temporal branches of maxillary artery. The zygomatic artery passes forwards close above zygoma, where it lies between the two layers of the temporal fas< It is distributed to the outer part of the orbicularis oculi muscle, anterior branch passes forwards and upwards in a tortuous man: and is distributed to the structures covering the frontal bone, wher anastomoses with the supra-orbital and supratrochlear branches 0T ophthalmic artery, and with its fellow of the opposite side, posterior branch takes an arched course upwards and backwa above the auricle, supplying the adjacent structures, and anas mosing with the posterior auricular and occipital arteries, and v its fellow of the opposite side (see Fig. 698).

The arteries of the scalp are peculiar in many ways. In the f


THE HEAD AND NECK


ii59


they are very superficial, lying in the fatty layer of the scalp

deep to the skin; they are thus very liable to injury, and in old le, where their walls are hardening and the superficial fat diminishthey may easily be seen in the temporal region, n the second place they are very tortuous, a condition which is lly associated with arteries supplying movable parts, and in ige this tortuosity increases.

'hirdly, they not only anastomose with one another, as most 'ies do, but they anastomose freely across the middle line, thus lg wonderful vitality to a piece of scalp which has been torn away >st completely.


L. Testut’s ‘ Anatomie Humaine ’).

fourthly, when cut they bleed most profusely, because their walls prevented from collapsing by the dense connective tissue between skin and the epicranium in which they lie. For this reason, too, difficult to pick them up when they have to be tied, fhe superficial temporal vein is formed in front of the auricle by union of an anterior and a posterior branch, the former communing freely with the supra-orbital and supratrochlear veins, and the T with the posterior auricular vein and the occipital venous plexus, ve the zygoma it is joined by the middle temporal vein, which inates in a plexus in the temporal fossa, and pierces the temporalis temporal fascia, receiving in its course the zygomatic vein. The Official temporal vein then descends over the zygoma and enters





n6o


A MANUAL OF ANATOMY


the parotid gland, within which it receives the auricular, articu and transverse facial veins. Finally, it joins the maxillary vein ah the level of the neck of the mandible to form the posterior facial's (temporo-maxillary vein).

Extrinsic Muscles of the Auricle.—These are three in number, follows: (i) auricularis superior; (2) auricularis anterior; and (3) aur: laris posterior.

Auricularis Superior (Attollens Aurem)— Origin. —The lateral par the epicranial aponeurosis and temporal fascia.

Insertion. —The inner or cranial surface of the auricle over convexity corresponding to the fossa of the antihelix on its 01 surface.

Nerve-supply. —The temporal branches of the facial nerve, posterior part of the muscle may be supplied by the posterior aurici branch of the facial nerve.

The muscle is very thin, pale, and fan-shaped, and. its fibres c verge in a downward direction.

Action. —To raise the auricle, though all the auricular muscles vestigial in man and practically functionless.

Auricularis Anterior (Attrahens Aurem)— Origin .—The lateral p of the epicranial aponeurosis in front of the auricularis superior, v which muscle it is continuous. Also from the temporal fascia.

Insertion. —The anterior part of the helix of the auricle.

Nerve-supply. —The temporal branches of the facial nerve.

The muscle is directed backwards.

Action. —To draw forwards the auricle.

Auricularis Posterior (Retrahens Aurem)— Origin. —The upper p of the outer surface of the mastoid process of the temporal bone.

Insertion. —The inner or cranial surface of the auricle over convexity of the concha.

Nerve-supply. —The posterior auricular branch of the facial nerv

The muscle is directed forwards.

Action. —To draw back the auricle.

The auricularis posterior is more distinct than the other two muse and is usually arranged in two bundles.

Behind the ear, in the mastoid region, which is not a part of scalp proper, there are certain structures which have some conned with the scalp. These comprise posterior auricular nerves (branc of the facial and vagus), posterior auricular vessels, and poste auricular lymph glands.

Posterior Auricular Nerve.—This is a branch of the facial ne; immediately after it emerges from the facial canal through the st; mastoid foramen. It passes upwards between the mastoid pro< and the auricle, where it lies deeply in company with the postej auricular artery, and it divides into two branches—auricular ; occipital. The auricular branch supplies the auricularis poste; muscle on its deep aspect, and those intrinsic muscles of the aur which lie on its inner or cranial aspect. It may also send a bra




THE HEAD AND NECK


1161


yards beneath the auricularis posterior to supply the posterior t of the auricularis superior. The occipital branch passes back■ds, lying deep to the lesser occipital nerve and posterior branch the great auricular, and supplies the corresponding half of the ipital belly of the occipito-frontalis muscle. The posterior auricular ve communicates with the lesser occipital and great auricular ves, and also with the auricular branch of the vagus.

The Auricular Branch of the Vagus Nerve (Nerve of Arnold). —This t branch of superior ganglion of the nerve. Having traversed the stoid canaliculus in the petrous part of the temporal bone, it srges through the tympano-mastoid fissure between the mastoid cess and tympanic plate, and then divides into two branches. One nch takes part in the supply of the inner or cranial surface of the icle, and also supplies the lower and back part of the external litory meatus; and the other branch joins the posterior auricular ve.

Posterior Auricular Artery. —This vessel is one of the two posterior nches of the external carotid artery, the other branch being the ipital artery. Having passed backwards and upwards on the loid process under cover of the parotid gland, it lies deeply between i mastoid process and the auricle in close relation to the posterior icular nerve, and divides into two branches—auricular and occipital, e auricular branch supplies the inner or cranial surface of the auricle i adjacent structures, and it anastomoses with the posterior branch the superficial temporal artery. The occipital branch passes backrds to the occipital belly of the occipito-frontalis muscle, and istomoses with the occipital artery.

The posterior auricular vein is of fairly large size, and returns the od from the lateral portion of the scalp posteriorly and the inner face of the auricle. Its radicles communicate with the occipital xus and with the posterior branch of the superficial temporal vein, e vessel passes downwards and forwards over the upper part of the rno-mastoid muscle, and terminates on this muscle about the level the angle of the mandible by joining the posterior division of the sterior facial vein to form the external jugular vein.

Mastoid Lymph Glands (Posterior Auricular Lymph Glands). These all glands lie close to the insertion of the sterno-mastoid muscle, ey receive their afferent lymphatics from the lateral part of the back the scalp and the back of the auricle, and their efferent lymphatics $s to the upper deep cervical lymph glands.

Temporal Fascia. —This is a strong aponeurosis which covers the nporalis. Superiorly it is attached from before backwards to the nporal border of the zygomatic bone, the superior temporal line of i frontal and parietal bones, and the supramastoid crest. of the nporal bone. Interiorly it divides into two laminae, which aie ached to the outer and inner margins of the upper border of the somatic arch. Between these two laminae there are a small amount adipose tissue, and the zygomatic branch of the superficial temporal


1162


A MANUAL OF ANATOMY


artery, and the zygomatico-temporal nerve. Superficial to the fasc there are the delicate prolongation of the lateral portion of the e] cranial aponeurosis and the auriculares superior et anterior muscl< with the superficial temporal vessels and auriculo-temporal nen Superiorly the fascia gives origin by its deep surface to superfic: fibres of the temporalis, but it is separated from that muscle towar the zygoma by fat.

The temporalis muscle is described on p. 1302.

Lymphatic Vessels of the Scalp—Frontal Region. —These pass the parotid lymph glands. The anterior lymphatics pass directly the parotid lymph glands, and the posterior lymphatics terminate in t mastoid lymph glands.

The Scalp as a Whole. —Before leaving the scalp it may be w< to review its general structure and to notice that it is made up of fi layers.

(1) The skin is very thick, and nee^6 a firm incision to penetrate:

(2) The subcutaneous tissue binds the skin closely to the epicrani aponeurosis, with which it moves; it contains lobular, granulated f in which are the bloodvessels and nerves as well as the roots of t. hair follicles. On account of the presence of the nerves as well as of t. density of the connective tissue any suppuration in this layer will strictly localized and very painful.

(3) The epicranial aponeurosis is formed by the very thin, flatten tendon of the occipito-frontalis muscle.

(4) The subaponeurotic layer, sometimes known to surgeons as t. ‘ dangerous layer * of the scalp, is composed of very loose connectf tissue, and is little more than a lymph space. The looseness of tj cellular tissue allows the first three layers to move freely over t] skull, and if septic matter reaches it and suppuration follows, t] pus readily spreads all over the space and tends to bag at the mo dependent points in front and behind. The absence of nerves and tl looseness of the tissue account for the little pain which accompani suppuration in this layer.

(5) The periosteum or pericranium covers the skull bones, and continuous with the dura mater at the sutures as long as these a unclosed. For this reason a subpericranial collection of blood pus will be limited to the area of one skull bone, while a subepicrani collection, as has been seen, has no such definition.

Basal Part of the Cranial Cavity.

Dura Mater on the Base of the Skull. —A full and general accoui of the membranes of the brain will be found on p. 1598 ^ se ^-> short description of the dura mater, as it is seen on the base of tl skull after removal of the brain, will be given here.

The dura mater is seen to be continuous with the falx cerebri in t middle line in front. Just outside this it covers the cribriform pla of the ethmoid at the bottom of a well-marked hollow which contai



THE HEAD AND NECK


1163

olfactory bulb. External to this it covers the irregularities of the tal plate of the frontal and the lesser wing of the sphenoid behind . In the middle fossa it lines the so-called ‘ optic groove/ and at

I end of this is carried into the optic foramina. Behind the groove >rms the diaphragma sella, covering the hypophyseal fossa, while

pierced by the internal carotid artery just behind the foramen.

diaphragma sellae shows a central hole for the infundibulum of hypophysis cerebri. The membrane is attached to the clinoid

esses and the interclinoid ligaments, and stretches outwards from
e to line the hollow of the greater wing and upper surfaces of the

•ous bone. It is carried upwards and forwards here to cover the erior orbital fissure and gain the lower aspect of the lesser wing, mall fold of dura mater projects from the edge of the lesser wing he sphenoid, the sphenoidal fold , and a small ‘ lunula ’ overhangs optic foramen. At the upper border of the petrous bone the nbrane projects upwards and inwards as the tentorium cerebelli, ch is a two-layered reflection of the dura mater. Below the torium it lines the posterior fossa, and presents apertures through ch all the nerves which come from the pons and medulla pass to

h their bony foramina. A small fold, the falx cerebelli, projects

he middle line behind. The dura mater becomes continuous with spinal dura at the foramen magnum, but the exact position of this mien is not easily distinguished when the membrane is in position, ng to the smooth, continuous slope formed by it as it passes from basi-occiput over the odontoid process and its ligaments into the tebral canal.

Certain structures lie deep to the dura mater, between it and the y skull— i.e., between the inner layer, which we have been consider, and the outer layer, which covers the bones. These are venous ises, nerves, and arteries. The venous sinuses on the base of the

II are (see p. 1603 et seq. for further details):

The sigmoid, running downwards and then forwards in the posterior >a to reach the jugular foramen.

The inferior petrosal, passing forwards and upwards from the ular foramen to the apex of the petrous bone along its lower edge. The superior petrosal, running forward along the upper edge of the rous bone at the base of the tentorium cerebelli.

The cavernous, placed on the side of the body of the sphenoid ere this joins the greater wing, and formed by the junction of the ) petrosal sinuses; in front it is continuous with the superior ophImic vein and with the spheno-parietal sinus, which lies in the fold lura mater along the lesser wing of the sphenoid.

The circular sinus is a spongy venous network which surrounds

pituitary body and connects the two cavernous sinuses.

The transverse sinus lies under the central basal dura mater, and n the form of a network joining the inferior petrosal sinuses.

The cranial nerves must necessarily pierce the dura mater to ch and pass through the base of the skull, and the situations of the


1164


A MANUAL OF ANATOMY


points of passage through the membranous and bony parts do n always correspond. Those nerves which leave the skull in relati( with the greater wing of the sphenoid pass through the dura mat at points some distance behind their bony foramina, and in the inte vening parts of their courses lie deep to the inner layer of dura mate lying near or in relation with the cavernous sinus. These nerv


Frontal Sinus


Anterior Fossa


Optic Nerve Ophthalmic Artery


Oculo-motor Nerve / •


Trochlear Nerve


Region of Cavum Trigeminale

Trigeminal Nerve


Facial Nerve

Auditory Nerve

G losso-pharyngeal Nerve

Vagus Nerve


Posterior Border c Small WingofSphi


Ant. Intercav., S: Hypophysis C« 


.-Cavernous S -- Abducent N


— Middle Foss


4 - - Basilar Plex


Sup. PetrosE Sinus

Inf. Petrosa] Sinus


" Sigmoid Sin


'•Cerebellar Fossa


Accessory Nerve


Transverse Sinus


Hypoglossal Nerve]


Cerebral Fossa


Spinal]Cord j Confluence of Sinuses Occipital Sinus


Fig. 699. —The Internal Base of the Skull, showing the Cranial Nervi

and Venous Sinuses.

are the oculo-motor, trochlear, trigeminal, and abducent; the oth< cranial nerves pierce the dura mater opposite their bony foramina.

It is not quite correct to say that the cranial nerves ‘ pierce ’ the dura mat at the places where their apertures of exit are seen; they carry out with the a covering from the membrane, so that they could be described rightly 1 evaginating it. The covering layer, however, is so thin in most cases, and so soon lost in the ordinary fibrous sheath of the nerve, that little exceptk is taken to the descriptive expression ‘ piercing.' In the case of the trigemin nerve, however, the evaginated covering of dura mater is better marked, and '















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1165

he whole, looser; it envelops the roots of the nerve and the trigeminal

jlion, and is known as the cavum trigeminale (.Meckel's cave). The cavum jminale, therefore, lies between the dura and the skull. The optic nerve, eover, should not be described as ‘ piercing ’ the membrane, for the eye and lervous stalk are developmentally parts of the brain itself, and the dura er is carried along the nerve to become directly continuous with the sclerotic

of the eye, which represents the same layer.

Some other nerves, such as the superficial petrosals and the nasoiry in a part of its course, lie deep to the dura mater, and will be bribed later.

All the meningeal vessels lie between skull and dura mater, and do pierce the inner membranous layer. The only things which pass Dugh this layer are the cranial nerves and the cerebral vessels; $e last are represented by (a) the internal carotid, which, lying irst between dura and bone with the cavernous sinus, pierces the nbrane medial to the anterior clinoid process to reach the brain;

. ( b ) the vertebral arteries, which pierce the membrane below the 11 and run up through the foramen magnum to reach the brain, tain cerebral veins pierce the dura mater at various points (see p. 8 ) to open into extradural sinuses.

Hie aqueduct of cochlea is described as passing through the dura to reach subarachnoid space, and the endolymphatic duct lies between the membrane the bone.

Cranial Nerves at the Base of the Skull. —The cranial nerves are inged in twelve pairs, and as they leave the cranial cavity they five sheaths from the meninges of the brain.

The olfactory bulb rests upon one half of the cribriform plate of ethmoid bone, with dura mater interposed. Through the fora1a of that plate it receives about twenty olfactory filaments, which

e as the axons of the olfactory cells of the olfactory mucous

[nbrane of the nasal fossa.

The optic nerve passes forwards and outwards from the optic asma to the optic foramen, through which it enters the orbit. It .ccompanied by the ophthalmic artery, which lies below and lateral t. Before reaching the foramen it is crossed by the anterior cerebral ery, and the internal carotid comes through the dura mater just dnd and lateral to it.

The third or oculo-motor nerve pierces the dura mater, which ns the upper and outer wall of the cavernous sinus, a little in front the posterior clinoid process of the sphenoid bone.

The fourth or trochlear nerve, of small size, pierces the dura mater a point a little behind the posterior clinoid process of the sphenoid ie, lateral to the third nerve, and in or just beneath the free margin the tentorium cerebelli. Afterwards it traverses the outer wall of

cavernous sinus.

The fifth or trigeminal nerve consists of two roots—sensory and tor. These two roots pierce the dura mater near the apex of the rous part of the temporal bone below the tentorium, and enter


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A MANUAL OF ANATOMY


a'recess of the dura mater, called the cavurn ingeminate (Meckel's cav where they will be presently described.

The sixth or abducent nerve pierces the dura mater £ inch behi the level of the posterior clinoid process, and near the apex of t petrous bone, where it enters the inferior petrosal sinus. It lies little to the inner side of the fifth nerve.

The seventh or facial nerve, the eighth or auditory nerve, accoi panied by the internal auditory artery, enter the internal meatus.

The ninth or glosso-pharyngeal nerve, the tenth or vagus ner and the eleventh or accessory nerve pass through the middle compa:


Fig. 700.—Showing the Venous Sinuses on the Petrous Bone, and

Relation with the Trigeminal Nerve.

Also shows great superficial petrosal nerve.

ment of the jugular foramen. This foramen is divided into thi compartments—namely, antero-medial, middle, and postero-later The antero-medial compartment gives passage to the inferior petro.j sinus. The middle compartment transmits the glosso-pharyngeal, vagi and accessory nerves, in this order from before backwards. T glosso-pharyngeal nerve pierces the dura mater separately, a receives special sheaths from the dura mater and arachnoid membrai The vagus and accessory nerves pass together through a sin^ aperture in the dura mater, and receive common sheaths from t dura and arachnoid membrane. The postero-lateral compartment trai








THE HEAD AND NECK


1167


5 the sigmoid sinus, which terminates in the internal jugular vein, the vein is deep to the dura, this part of the foramen cannot be 1 directly when the dura mater is in position.

The twelfth or hypoglossal nerve pierces the dura mater in two dies, which pass through separate apertures. As these bundles 5 through the anterior condylar canal they unite to form one nerve, ween the points of exit of the hypoglossal and the last three nerves jugular tubercle is seen, forming a very useful landmark.

Structures passing through the Foramen Magnum. —(1) The medulla mgata, with its membranes, passes out and becomes the spinal i. (2) The spinal root of the accessory nerve of either side, having mded from the interval between the posterior roots of the cervical lal nerves and the ligamentum denticulatum, enters the cranial ity. It then turns outwards behind the jugular tubercle to the Idle compartment of the jugular foramen, where it meets the rial root of the nerve, with which it becomes closely connected it passes through the foramen. (3) The vertebral artery of each j enters the cranial cavity after having pierced the dura mater. The two anterior spinal branches of the vertebral arteries descend the front of the medulla oblongata, and, inclining inwards towards h other, they unite in passing through the foramen magnum to n the anterior spinal artery, the membrana tectoria, and the apical ment of the odontoid process.

Trigeminal Ganglion (Gasserian Ganglion) (Fig. 700).—The trilinal ganglion occupies the trigeminal impression (Gasserian imssion) on the superior surface of the petrous part of the temporal Le near the apex, where its posterior part lies in a recess of the a mater, called the cavum trigeminale ( Meckel’s cave). It is someit semilunar, being convex in front and concave behind, and measures y \ inch from before backwards. It is associated with the sensory t of the fifth nerve, which, before entering the posterior concave ect of the ganglion, becomes expanded, its fasciculi at the same e becoming separated and assuming a plexiform arrangement, lially the ganglion is intimately related to the back part of the ernous sinus, and by its inner and lower aspect to the internal otid artery in the foramen lacerum, and on this aspect it receives icate filaments from the internal carotid sympathetic plexus. The tor root of the fifth nerve, small in size, lies below the deep surface

he ganglion; but there is no blending of the two sets of fibres, the

tor root passing independently in an outward direction to the imen ovale. The greater superficial petrosal nerve, on its way to foramen lacerum, passes beneath the ganglion, though not in the r um trigeminale.

The ganglion contains cells similar to those of a spinal ganglion, 1 it receives its blood from the middle and accessory meningeal eries. It is important in connection with modern surgery to notice ■t the front part of the ganglion does not lie in the cavum trininale, but has a close investment of dura mater. Hence the front


1168


A MANUAL OF ANATOMY


part may be removed without opening the subarachnoid space allowing cerebro-spinal fluid to escape.

Branches. —The branches of the ganglion arise from its anteri convex aspect, and are known as divisions. They are as follow the first or ophthalmic division; the second or maxillary divisio and the third or mandibular division. The ophthalmic and maxilla nerves are entirely sensory, but the mandibular nerve, being join by the motor root, is both sensory and motor.

The first division of the trigeminal nerve, or the ophthalmic ner\ is the smallest of the three branches of the ganglion. It passes fc wards in the outer wall of the cavernous sinus, where it lies below t] fourth nerve. On approaching the superior orbital fissure it divid into branches in the following order from behind forwards: (i) nas ciliary (nasal), (2) lacrimal, and (3) frontal. All these three branch enter the orbit through the superior orbital fissure. As the ophthaln nerve passes forwards it receives a communicating branch from t' internal carotid sympathetic plexus, and it furnishes the nervus tento> to the tentorium cerebelli. It also communicates with each of t oculo-motor, trochlear, and abducent nerves.

The naso-ciliary nerve, having passed through the orbit, re-ente the skull by running between the orbital plate of the frontal and t' upper surface of the ethmoid. It then lies deep to the dura mater < the cribriform plate near its anterior extremity, and soon disappea by passing down between this bone and the nasal area of the frontal

The second division of the trigeminal nerve, or the maxillary ner (superior maxillary nerve), passes horizontally forwards for a she distance in the lower part of the outer wall of the cavernous sinus, ai it leaves the cranial cavity through the foramen rotundum, whi leads to the pterygo-palatine fossa. Before leaving the cranial cavi it furnishes the delicate meningeal nerve to the dura mater of tl middle fossa.

The third division of the trigeminal nerve, or the mandibular ner (inferior maxillary nerve), is the largest of the three branches of t. ganglion. It passes downwards to the foramen ovale, through whi it leaves the cranial cavity, and so enters the infratemporal foss It is accompanied by the motor root of the fifth nerve, which joi it as it passes through the foramen ovale. The nervus spinosus fre the mandibular nerve is not given off until after the parent trui has issued through the foramen ovale, and it enters the cranial cavi through the foramen spinosum in company with the middle meninge artery. It then divides into two branches, anterior and posterior. T anterior branch supplies the dura mater over the greater wing of t sphenoid bone, and the posterior branch passes through the fissr between petrous and squamous parts of the temporal bone to supp the mucous membrane of the mastoid air-cells.

Greater Superficial Petrosal Nerve. —This nerve is a branch of the gangli of the facial nerve in the facial canal. It enters the middle fossa of the be of the skull through its hiatus, and passes forwards and inwards in a groove


THE HEAD AND NECK


1169


anterior surface of the petrous part of the temporal bone. Having passed sath the trigeminal ganglion embedded in the dura mater, it enters the upper of the foramen lacerum, where it is placed on the outer side of the internal tid artery, and it joins the deep petrosal nerve from the internal carotid pathetic plexus. In this manner the nerve of the pterygoid canal is formed,

h enters the latter canal by its opening on the anterior aspect of the foramen

rum, and so reaches the spheno-palatine ganglion in the pterygo-palatine i. The greater superficial petrosal nerve is accompanied by the superficial osal branch of the middle meningeal artery.

jesser Superficial Petrosal Nerve. —This nerve represents the continuation ugh the tympanic plexus of the tympanic branch (Jacobson's nerve) of the 30-pharyngeal nerve. It is reinforced by a small branch from the ganglion he facial nerve, Avhich joins it as it traverses a small canal in the petrous of the temporal bone beneath the canal for the tensor tympani muscle, nerve enters the middle fossa through a small opening on the lateral side he hiatus for the greater superficial petrosal nerve. It then passes for a 3 forwards and inwards, and leaves the cranial cavity through the canaliculus iminatus (when present), or through the fissure between the petrous temporal the greater wing of the sphenoid, or, it may be, through the foramen ovale, r which it terminates in the otic ganglion.

External Petrosal Nerve. —This nerve, which is inconstant, passes from the pathetic plexus on the middle meningeal artery backwards and outwards

he anterior surface of the petrous part of the temporal bone, and it leaves

cranial cavity through a minute aperture situated within the thin margin tie hiatus for the greater superficial petrosal nerve. It ends in the ganglion re facial nerve.


Interior of the Cavernous Sinus.—The interior of this sinus ia ken up by a network of delicate trabeculae. The outer wall of sinus contains the following rial nerves, in order from above mwards: the oculo-motor, the ihlear, the ophthalmic division

he trigeminal, and the maxilr division of the fifth. These

ves, as they pass forwards, separated from the bloodrent by the endothelial lining the outer wall of the sinus.

J cavity of the sinus is travel by (1) the cavernous portion the internal carotid artery, rounded by a plexus of symhetic filaments; and (2) the Lucent nerve, which lies in >e contact with the outer side of the artery. These structures are ) separated from the blood-current by the endothelial lining of the is.

For the processes and other sinuses of the dura mater see p. 1601. Cavernous Portion of the Internal Carotid Artery.—This part of the irnal carotid artery lies within the cavernous sinus, which occupies carotid groove on the lateral aspect of the body of the sphenoid ie. It is separated from the blood-current by the endothelial

74


Internal Carotid Artery Abducent.Nerve Oculo-motor Nerve Trochlear Nerve Ophthalmic Nerve


Sella Turcica


Maxillary Nerve

Left Sphenoidal Sinus

Fig. 701.—Diagram of the Left Cavernous Venous Sinus and its Outer Wall, showing the Relative Positions of the Contained Structures (Posterior View).



1170


A MANUAL OF ANATOMY


lining of the sinus. The course of the vessel is at first upwan between the lingula of sphenoid and the posterior petrosal process the sphenoid; then forwards as far as the anterior clinoid process the sphenoid; and finally upwards medial to the anterior clinc process. In the latter situation it pierces the dura mater, whi forms the roof of the cavernous sinus, and enters upon the cerebi part of its course.

The vessel is accompanied by the internal carotid sympathe plexus, and the abducent nerve lies in close contact with its out side, all being invested by the endothelial lining of the sinus.


Fig. 702.—Right Internal Carotid put in Position on Base of Skui

and Crossed by Sixth Nerve.

Great superficial petrosal nerve is also seen.

Branches.—These are as follows: hypophysial, to the hypophys cerebri; ganglionic, to the trigeminal ganglion; cavernous, to the w£ of the cavernous sinus, and to the oculo-motor, trochlear, trigemim and abducent nerves; meningeal, to the dura mater of the midd cranial fossa; and the ophthalmic artery. The latter vessel arises fro: the cavernous portion of the internal carotid on the inner side of tl anterior clinoid process, and it enters the orbit, with the optic nerv through the optic foramen, lying at first beneath the nerve, and the on its outer side.

The Medial Part of the Internal Carotid Sympathetic Plexus (Caveri ous Plexus).—This plexus is situated principally on the inner and low< aspects of the bend which the cavernous portion of the internal caroti





THE HEAD AND NECK


1171


•y describes medial to the anterior clinoid process. Its branches as follows; (1) vascular, to the internal carotid artery and its ches; (2) hypophysial, to the hypophysis cerebri; (3) communing, to the oculo-motor, trochlear, ophthalmic division of the tri[nal, and abducent cranial nerves; and (4) the sympathetic root of

iliary ganglion. The last-named branch enters the orbit through

superior orbital fissure.

"he hypophysis cerebri (pituitary body) is a small oval mass which tuated in the hypophysial fossa, or sella turcica, of the sphenoid It lies under cover of a circular fold of the dura mater, called the hragma sellce, in the centre of which is an opening for the passage le infundibulum. Its long measurement extends transversely, and msists of two lobes—anterior and posterior. The anterior lobe is larger of the two, and the posterior lobe is connected with the rior part of the tuber cinereum by means of the infundibulum, rhe infundibulum projects downwards from the anterior part of tuber cinereum to the posterior lobe of the pituitary body. Its sr part is hollow, and contains mnel-shaped diverticulum of the ty of the third ventricle.

tructure. —The anterior lobe consists of ral tubules lined with epithelium, and sted by capillary bloodvessels. The jrior lobe, though developed from the 1, is destitute of nervous elements. It imposed of a reticulum of connective e, which contains branched cells. Bern the two lobes is the middle part.

)evelopment. —The anterior lobe is deped from a diverticulum of the buccal tomatodaeal ectoderm, which is known ie pouch of Rathke. The diverticulum rs upwards, and, when the cranio•yngeal canal of early life becomes closed, connection of the diverticulum with the

al ectoderm is severed. The diverurn later on becomes converted into

lies, which form the anterior lobe, dhe Brior lobe of the pituitary body and the ndibulum, which is connected with it, are sloped as a diverticulum which grows nwards from that part of the diencephalon

h forms the floor of the third ventricle. #

cavity of the diverticulum remains permanent in the upper part of its ndibular portion, but elsewhere it becomes obliterated. The lower part of diverticulum thereafter becomes converted into a reticulum of connective ie with branched cells, which forms the posterior lobe.


Fig. 703. —Diagram of Anteroposterior Section through the Hypophysis.

A, anterior lobe: PT, its pars tuberalis. Pars Interm., pars intermedia. N, neural or posterior lobe. INF, infundibulum. OPT. CH, optic chiasma.


Side of the Neck.

The side of the neck has a quadrilateral outline, the boundaries which are as follows: superior, the lower border of the mandible . a line prolonged from the angle of that bone over the mastoid


1172


A MANUAL OF ANATOMY


process to the inner third of the superior rruchal line of the occipi bone; inferior , the clavicle and one half of the upper border of 1 manubrium sterni; anterior , the middle line of the neck; and posteri the outer border of the trapezius in the neck.

Landmarks.—The body and angle of the mandible can easily felt, and the clavicle, together with the upper border of the manubrii sterni, is conspicuous. A deep depression, called the supraster: fossa, is perceptible above the upper border of the manubrium ster lying between the sternal h'eads of origin of the sterno-mastoid muscl The outline of the sterno-mastoid muscle is readily discernible when 1 head is turned so as to direct the face towards the opposite should The muscle extends in a diagonal direction from the sterno-clavicu joint to the mastoid process and outer half or two-thirds of the super nuchal line of the occipital bone, and it divides the side of the ne into two triangles—anterior and posterior. A small triangular inter may be felt between the sternal and clavicular heads of origin of t sterno-mastoid just above the inner end of the clavicle, in which t common carotid artery and internal jugular vein lie deeply. T external jugular vein crosses the sterno-mastoid muscle in the directi of a line extending from a point just behind the angle of the mandil to a point above the centre of the clavicle, and it is accompanied the superficial cervical glands. The common carotid artery lies unc cover of the anterior border of the sterno-mastoid muscle in the directi of a line drawn from the sterno-clavicular joint to a point midw between the angle of the mandible and the tip of the mastoid proc( of the temporal bone. The vessel extends along this line as high the level of the upper border of the thyroid cartilage, above which is replaced by the external carotid artery. The internal jugular vt is close to the outer side of the common carotid artery, and the vag nerve lies deeply between the two vessels. If deep pressure is ma over the common carotid artery on a level with the cricoid cartila of the larynx, the anterior tubercle of the transverse process of t sixth cervical vertebra may be felt. It is known as the carotid tuber (of Chassaignac.)

The bifurcation of the innominate artery lies behind the upp border of the right sterno-clavicular joint, and the left common carol artery lies behind the left sterno-clavicular joint, while the lower pa of the internal jugular vein on each side is behind the inner end the clavicle. Near the middle line of the neck the anterior jugul vein descends vertically. The spinal root of the accessory ner passes downwards and outwards beneath the anterior border of t sterno-mastoid to pierce the deep part of that muscle at about t junction of the upper fourth and lower three-fourths. The nerve met with fully 1 inch below the tip of the mastoid process, and in t direction of a line let fall vertically from the mastoid tip. It is ve nearly on a level with the body of the hyoid bone. Along the posteri border of the sterno-mastoid some superficial cervical lymph glan may be felt.


THE HEAD AND NECK


ii 73


Important structures occupy the middle line of the neck, and can usually distinguished without difficulty. These are as follows, in sr from above downwards: (1) the body of the hyoid bone, lying

below the mandible, and having the greater horn projecting

kwards and upwards on either side; (2) the thyro-hyoid membrane; the thyroid cartilage, with its laryngeal prominence (pomum imi) in the middle line, leading up to the V-shaped thyroid notch the upper border, and its expanded ala on either side, each of which s behind in a superior and an inferior horn; (4) the crico-thyroid ment; (5) the narrow anterior part of the cricoid cartilage, which icides with the level at which the superior belly of the omo-hyoid


scle crosses the carotid sheath; and (6) the rings of the trachea, ich, however, are covered superiorly by the isthmus of the thyroid nd, and inferiorly by the sterno-hyoid and sterno-thyroid muscles 1 adipose tissue.

The lateral lobes of the thyroid gland may be felt on either side of larynx and trachea as low as about the fifth ring; and in young Idren the thymus extends upwards upon the trachea for some tance above the manubrium sterni.

The greater horn of the hyoid bone is the guide to the lingual artery , hypoglossal nerve for operative purposes, the structures lying just ve the greater horn.





A MANUAL OF ANATOMY


1174

The upper border of the thyroid cartilage is on a level with the di between the bodies of the third and fourth cervical vertebra.

The narrow anterior part of the cricoid cartilage is on a level wi the disc between the bodies of the fifth and sixth cervical vertebrae, which level the pharynx becomes the oesophagus. In this situatior foreign body, when swallowed, is liable to become impacted.

Below the cricoid, in the middle line, one or two rings of the trach may be felt above the thyroid isthmus, and it is here that a hi tracheotomy is performed, an easy operation since the windpipe is


Fig. 705. —Superficial Dissection.


close to the skin. Below the isthmus the trachea rapidly recedes, that a low tracheotomy is often a difficult and sometimes a ve dangerous operation; dangerous because, often in children and son times in the adult, the left innominate vein lies in the suprasterr region above the level of the manubrium sterni, and so in the way the knife. Ignorance of this fact has meant, and may mean aga the loss of a life.

Above the middle third of the clavicle, between the sterno-mash and trapezius muscles, there is a depression known as the greai



THE HEAD AND NECK


ii 75


aclavicular fossa, which indicates the position of the subclavian lgle, with the third part of the subclavian artery and the trunks ie brachial plexus of nerves.

Platysma (Platysma Myoides)— Origin .—The superficial fascia which >rs the clavicular parts of the pectoralis major and deltoid muscles. Insertion. —(1) The outer part of the body of the mandible from symphysis menti to the anterior border of the masseter muscle; (2) the angle of the mouth, where the fibres blend with those of depressor anguli oris and orbicularis oris.

Nerve-supply .—The cervical branch of the facial nerve, which comlicates with branches of the anterior cutaneous nerve of the neck. The fibres are directed upwards and forwards or inwards over the dele and side of the neck.

Action. —(1) To draw the angle of the mouth downwards and outds; (2) to act as a feeble depressor of the mandible; (3) to raise the 1 of the neck and upper pectoral region as far out as the acromion cess, throwing it into obliquely-disposed folds.

The muscle forms an extensive, thin, pale sheet, which is embedded hin the superficial fascia. In the region of the symphysis menti innermost fibres decussate across the middle line with those of the >osite side, the fibres of the right muscle being superficial. The scle covers the external and anterior jugular veins, the superficial nches of the cervical plexus of nerves, the subclavian triangle, and sterno-mastoid, sterno-hyoid, omo-hyoid, and digastric muscles.

The platysma in man is a remnant of a subcutaneous muscular sheet, called panniculus carnosus, which exists in many animals, and by which the twitchof the skin is produced.

Jugular Veins.—The jugular veins are four in number on either e—anterior, external, posterior external, and internal.

The anterior jugular vein begins in the roof of the digastric triangle, Lere it is formed by the union of radicles which communicate with 3 submental vein, and are joined by radicles which have descended >m the structures over the body of the mandible. It descends rtically near the median line, lying at first superficial to the deep rvical fascia, but subsequently entering the suprasternal space. II en describes a bend, and, passing outwards behind the sternoistoid muscle, and in front of the scalenus anterior, it opens to the lower part of the external jugular vein. It may, however, >en into the subclavian vein. It communicates with the external gular vein by one or more tributaries, and usually receives a branch 3 m the facial vein which descends along the anterior border of the erno-mastoid and joins it towards the lower part of the neck, urther, it communicates with its fellow, of the opposite side by a ansverse branch, the jugular arch, which crosses in front of the achea, and lies in the suprasternal space.

The anterior jugular veins are usually asymmetrical, one or other sing of small size. Occasionally there is only one vein, which divides


A MANUAL OF ANATOMY


1176

into two vessels interiorly. The anterior jugular vein is destitute ^ valves.

The external jugular vein commences close behind the angle of tl mandible in the substance of the parotid gland, where it is formed t the union between the posterior division of the posterior facial ve: and the posterior auricular vein. On leaving the parotid gland descends almost vertically to a point above the centre of the clavicl In its course the vessel crosses the sterno-mastoid muscle, lying supe ficial to its sheath, and deep to the superficial fascia containing tl fibres of the platysma. At this level the main part of the anteri<


Fig. 706. —Superficial Veins of Neck.

SF, CF, superficial and common facial. TM, posterior facial or temporo-maxillar PA, posterior auricular. PJ, EJ, AJ, posterior, external, and anterior juguls

cutaneous nerve of -the neck runs forward deep to the vein, and offse of the nerve pass superficial to it. Having crossed the sterno-masto muscle, the vein descends not far from its posterior border, where lies in the roof of the subclavian triangle over the third part of tl subclavian artery. Up to this point the vessel is superficial to tl deep cervical fascia, but it now pierces that fascia and opens into tl subclavian vein.

The course of the external jugular vein is indicated by a line draw from a point close behind the angle of the mandible to a point abo^ the centre of the clavicle. Its tributaries are as follows: (1) poster!




THE HEAD AND NECK


1177


3rnal jugular, which joins it about the middle of the neck; (2) trans;e cervical; (3) suprascapular; and (4) anterior jugular, the latter

e joining it not far from its termination. It also communicates

1 the anterior jugular vein by one or more branches. The vessel rovided with valves, both at its termination and about i\ inches ve this point, and the transverse cervical and suprascapular veins


isterior Auricular Lymph Glands

Occipital Vein

al Lymph Gland

>r Auricular Vein

terior Division of

erior Facial Vein

iperficial Cervical Lymph Glands


osterior External Jugular Vein

mal J ugular Vein


rse Cervical Vein_



P, ,

whi 1 \n\


_Supratrochlear Vein

-Supra-orbital Vein

- Angular Vein


Superficial Temporal Vein Maxillary Vein


Posterior Facial Vein Anterior Facial Vein

Ant. Div. of Posterior Facial Vein

Submandibular Lymph Glands

Common Facial Vein Internal J ugular Vein Lingual Vein

Superior Thyroid Vein


Middle Thyroid Vein


Anterior Jugular Vein

. Suprasternal Lymph Gland


. 1 ■"


Suprascapular Vein and.Supraclavicular; Lymphatic Glands


r. 707. —The Superficial Veins and Superficial Lymph Glands of the

Right Side of the Head and Neck.

The platysma muscle has been removed.


i also furnished with valves where they open into the external

ular vein, or near their orifices.

The external jugular vein is sometimes very small, or even absent, I it may communicate with the cephalic vein by a vessel which sses over the clavicle.

r

Development. —The external jugular vein was formerly regarded as being sloped from the anterior cardinal vein; but according to most authorities anterior cardinal vein gives rise to the internal jugular vein, the external ular being of later development.








A MANUAL OF ANATOMY


1178

The posterior external jugular vein represents the most exter: occipital vein, and is formed by tributaries which issue from the ou part of the occipital plexus, reinforced by veins from the superfic structures at the back of the neck. It usually receives the mast' emissary vein and passes downwards and forwards, joining the exter: jugular vein about the middle of the neck.

The internal jugular vein will be found described on p. 1211.

Superficial Cervical Lymph Glands.— These are about six in numb and they lie upon the sterno-mastoid muscle, along the course of 1 external jugular vein, and deep to the superficial fascia and platysi muscle. They receive their afferent lymphatics from the adjac< superficial structures, the occipital and mastoid lymph glands, a some of those of the parotid and submandibular lymph glands. Tb efferent lymphatics pass to the deep cervical lymph glands.

Deep Cervical Fascia. —The deep cervical fascia is divided ii (1) a superficial investing layer, which completely invests the neck the form of a collar; and (2) deep processes or laminae, which inv the muscles, viscera, and chief bloodvessels and nerves.

Investing Layer. —This layer is attached posteriorly to the li\ mentum nuchae; superiorly to (1) the superior nuchal line of the oc pital bone, (2) the mastoid process of the temporal bone, (3) the zyj matic arch, and (4) the body of the mandible, under cover of 1 platysma, as far forwards as the symphysis menti; and interiorly the clavicle and upper border of the manubrium sterni, being pierc above the centre of the clavicle by the external jugular vein. Ale the middle line of the neck anteriorly it is continuous with the invest] layer of the opposite side.

The investing layer invests the cervical portion of the trapezi and from the anterior border of that muscle it passes forwards 0 1 the posterior triangle of the neck to the posterior border of the sten mastoid. In doing so it furnishes a deep process, which ensheat] the inferior belly of the omo-hyoid muscle. This process also embra^ the intermediate tendon of that muscle, after which it passes dov wards and inwards to be attached to the back of the inner end of 1 clavicle and the first rib. In this manner the horizontal position the inferior belly of the omo-hyoid is accounted for. When the vesting layer of the deep cervical fascia reaches the posterior bore of the sterno-mastoid it splits into two laminae, which ensheathe tl muscle, the superficial lamina being underneath the external jugu vein and platysma. At the anterior border of the sterno-mastoid 1 two laminae reunite, and the fascia passes forwards over the anter triangle of the neck to the median line, where it is continuous with 1 corresponding layer of the opposite side.

Between the upper part of the anterior border of the sterno-masb and the angle of the mandible the investing layer is of considera strength, and draws that border of the muscle forwards and upwar so as to render it convex and keep it over the line of the leading vess< Between the mastoid process and the angle of the mandible the



THE HEAD AND NECK


1179


ting layer is prolonged upwards over the parotid gland as the parotid

ia, which is very dense, and is attached superiorly to the lower

der of the zygomatic arch.

Below the level of the thyroid gland the investing layer divides 0 two laminae, anterior and posterior, both of which are superficial the infrahyoid muscles. At the middle line these laminae are conuous with those of the opposite side, and inferiorly they are attached the anterior and posterior margins of the upper border of the nubrium sterni. Between them there is an interfascial interval, led the suprasternal space (space of Burns). This interval contains

olar tissue, one or more lymphatic glands, the lower portions of the

terior jugular veins, with the jugular arch which here connects im, and the sternal heads of the sterno-mastoid muscles.

Deep Processes or Laminae.— The deep laminae, as stated, invest the iscles, viscera, and chief bloodvessels and nerves. The most imrtant are derived from that lamina of the investing layer which ms the posterior wall of the sheath of the sterno-mastoid muscle, d they are three in number—namely, carotid sheath, pretracheal icia, and prevertebral fascia—all of which have an intimate initial nnection.

The carotid sheath contains in separate compartments (1) the mmon carotid artery and the constituents of the ansa hypoglossi, the internal jugular vein, and (3) the vagus nerve, the latter being ntained within the back part of the septum, which separates the tery from the vein.

The pretracheal fascia, which is at first intimately connected with e anterior wall of the carotid sheath, passes forwards behind the frahyoid muscles, in which situation it splits to ensheathe the yroid gland, trachea, and oesophagus, and then it passes to the sdian line, where it is continuous with the pretracheal fascia of the •posite side. The pretracheal fascia is attached superiorly to the >dy of the hyoid bone, and inferiorly it descends over the trachea Ld bloodvessels into the superior mediastinum of the thorax, where it ends with the fibrous pericardium.

The prevertebral fascia, which is at first intimately connected with e posterior wall of the carotid sheath, passes forwards behind the larynx and oesophagus, and in front of the prevertebral muscles, t the middle line it is continuous with the corresponding fascia of e opposite side; superiorly it is attached to the base of the skull; id inferiorly it descends over the longus cervicis muscle into the isterior mediastinum of the thorax. Along a line corresponding to le inner wall of the carotid sheath the pretracheal fascia furnishes a condary lamina, called the bucco-pharyngeal fascia, which covers ie constrictor muscles of the pharynx and the buccinator muscle, etween the bucco-pharyngeal and prevertebral fasciae there is an terval, called the retro-pharyngeal space, which contains the loosely 'ranged connective tissue uniting the two fasciae. This space extends high as the base of the skull, and inferiorly is continuous with the


ii8o


A MANUAL OF ANATOMY


posterior mediastinum of the thorax. Another process of the pi vertebral fascia passes downwards and outwards in front of t scalenus anterior muscle. After this it invests the third part of t subclavian artery and subclavian vein, together with the nerve-trun of the brachial plexus, and, passing behind the clavicle, it becom continuous with the axillary sheath, which latter blends with t posterior aspect of the clavi-pectoral fascia. In the region of the su clavian triangle there is an interfascial space between this proce of the pretracheal fascia and the investing layer of the deep cervic fascia. This space extends downwards behind the clavicle to the poi where the axillary sheath and clavi-pectoral fascia join. It contai


Stemo- thyroid Sterno-hyoid

Investing Layer of Deep Cervical Fascia Superior Belly of Omo-hyoid Pretracheal Fascia Prevertebral Fascia


Suprasternal Space Trachea

Muscular Compartment

Lateral Lobe of Thyroid Gland


Carotid Sheath


Scalenus Anterior


Scalenus Medius


Levator Scapulae

Semispinalis Capitis


(Esophagus

Descendens hypoglossi ^ Common Carotid Artery Internal Jugular Vein - Vagus Nerve Platysma


Splenius


Sympathetic Trunk

Longus Cervicis - Stemo-mastoid


External Jugular V<


' Vertebral Vessels


Trapezius


Semispinalis Cervicis


Tig. 708. Diagram of a Transverse Section of the Neck at the Lev of the Sixth Cervical Vertebra, showing the Arrangement of ti Deep Cervical Fascia and the Positions of Other Structures.


the inferior belly of the omo-hyoid muscle, the suprascapular ar transverse cervical vessels, the lower part of the external jugular vei and the terminal portion of the anterior jugular vein.

Interfascial Compartments. —It has been stated that the det cervical fascia reaches the median line of the neck anteriorly in thr layers—namely, investing (in two divisions), pretracheal, and pr vertebral. It is therefore evident that there are four interfasci compartments as follows: (1) the suprasternal space (space of Burn! which is situated between the two divisions of the investing layer, ai contains the structures already enumerated; (2) the muscular cor partment, which is situated between the investing layer and the pr tracheal layer, and contains the infrahyoid muscles; (3) the viscer





















THE HEAD AND NECK


1181


partment, which lies between the pretracheal and prevertebra rs, and contains the larynx, trachea, thyroid gland, pharynx, phagus, and carotid sheath, the retro-pharyngeal space being in subdivision of this compartment behind the bucco-pharyngeal ia; and (4) the vertebral compartment, which lies between the vertebral layer and the attachment of the fascia to the ligamentum iae posteriorly, and contains the vertebral column, spinal cord, and vertebral and postvertebral muscles.

rhe suprasternal and muscular compartments are shut off from thoracic cavity. The visceral compartment in front of the trachea mtinuous with the superior mediastinum of the thorax, and behind oesophagus it, along with the retro-pharyngeal space, is continuous 1 the posterior mediastinum.

Parotid Process of the Deep Cervical Fascia. —This process is given a little below the angle of the mandible, and it passes upwards on deep surface of the parotid gland to the skull. Along with the Dtid fascia superficial to the gland it forms a dense sheath which ely invests the glandular substance. The parotid process furnishes aths to the posterior belly of the digastric, styloid, and pterygoid scles, and it also gives an investment to the superficial part of the mandibular gland. Connected with the parotid process there are sral bands, usually called ligaments, which are as follows: (1) sphenoadibular; (2) stylo-mandibular; (3) pterygo-mandibular; and

pterygo-spinous.

The spheno-mandibular ligament will be described in connection h the mandibular joint, of which it is sometimes regarded as an essory medial ligament (see p. 1316).

The stylo-mandibular ligament extends from the styloid process of temporal bone near its tip to the angle and adjacent part of the terior border of the ramus of the mandible, where it is placed ween the masseter and internal pterygoid muscles.

The pterygo-mandibular ligament is a narrow band which extends hi the hamulus of the medial pterygoid plate of the sphenoid bone the posterior extremity of the mylo-hyoid line of the mandible $e to the last molar socket. Anteriorly it gives origin to fibres of buccinator muscle, and posteriorly to fibres of the superior condor muscle of the pharynx.

The pterygo-spinous ligament is a narrow band which extends from harp spine on the posterior border of the lateral pterygoid plate of sphenoid bone, towards its upper part, to the spine process of the lenoid. This ligament is liable to become ossified.

The foregoing description is orthodox and traditional, and every fact stated be demonstrated by a good dissector; but there are some observers who 3rd the whole of these fascial planes as artifacts, and believe that all the irstices between the structures in the neck are filled with loose connective ue which, when it is cleaned from the surrounding parts, collapses into Y definite sheets. If this is the case, it should be possible, by varying the action of the incisions, to produce sheets in any plane. As a matter of fact, > can be done.


Il82


A MANUAL OF ANATOMY


Sterno-mastoid — Origin .—The sternal head, which is narrow ar round, arises from the upper and outer part of the anterior surfa* of the manubrium sterni. It is tendinous in front, and fleshy behin The clavicular head, which is broad and flat, arises from a rough rid| about ij inches long on the upper surface of the clavicle at its inn end.

Insertion .—The outer surface of the mastoid process of the ter poral bone, and the superior nuchal line of the occipital bone ov about its outer half or two-thirds.


Fig. 709. —Showing Sterno-mastoid and the Muscular Floor of

Posterior Triangle.



Nerve-supply .—The accessory nerve, and a branch from the cervic plexus, more particularly from the anterior primary ramus of the secor cervical nerve.

The spinal root of the accessory nerve passes deep to the anteri border of the muscle fully 1 inch below the tip of the mastoid proces and in passing downwards and backwards it pierces the deep part the muscle, giving off as it does so its branches to it.

The muscle is directed upwards, outwards, and backwards.

Action .—To flex the head towards the side on which the muse





THE HEAD AND NECK


1183

aced, the face being turned towards the opposite side. This is position of the head in torticollis or wry-neck, a condition which be due to an organic contraction to the muscle, affecting both s, or, it may be, the sternal head alone. When both muscles act ther from their origin they flex the head towards the thorax, when the head has been already thrown back the sterno-mastoid ls capable of extending it still farther instead of flexing it. It t be remembered, however, that a certain amount of flexion of lead may take place between any of the cervical vertebrae. When muscles act together from their insertion they elevate the upper of the anterior thoracic wall in forced inspiration.

"he sternal and clavicular heads are separated by a triangular Jar interval for a short distance above the sterno-clavicular joint, before their junction the fibres of the clavicular head to a large nt pass behind those of the sternal head, so that overlapping s place. The muscle is surrounded by a strong sheath, which is led by the deep cervical fascia. The platysma covers a large part

, and the external jugular vein, the anterior cutaneous nerve of
and great auricular nerves, and the superficial cervical lymph

ds are related to its superficial surface under cover of the platysma. principal deep relations are as follows: in the lower part of the

it covers the first and second parts of the subclavian artery, the

10-hyoid, sterno-thyroid, omo-hyoid, and scalenus anterior muscles, l the phrenic nerve lying upon the last-named muscle. In this rtion it also covers the anterior jugular vein, and the transverse ical and suprascapular arteries. Higher up it covers the cervical

us of nerves, the levator, scapulae, scalenus medius, and scalenus

erior muscles, and the accessory and the hypoglossal nerves. At insertion it covers the splenius capitis, longissimus capitis, and

erior belly of the digastric muscles, and a portion of the occipital

ry, in this order from the surface downwards. The anterior border he muscle forms the posterior boundary of the anterior triangle of neck, and covers the carotid sheath, with its contents, as high as level of the upper border of the thyroid cartilage ; and above that 1 it covers the external and internal carotid arteries. This border overlaps slightly the lateral lobe of the thyroid gland.. The

erior border forms the anterior boundary of the posterior triangle

he neck, and along it there lie the following structures: the superI cervical lymph glands, the lesser occipital nerve, great auricular, nrior cutaneous nerve of neck, the accessory, and the descending srficial branches of the cervical plexus of nerves, and a portion of external jugular vein.

The sterno-mastoid muscle, from its diagonal position upon the

of the neck, divides the quadrilateral space into two triangles terior and anterior.

Posterior Triangle. —This is the region which lies behind the sterno>toid muscle.

Boundaries — Anterior. —The posterior border of the sterno-mastoid.


A MANUAL OF ANATOMY


1184

Posterior .—The anterior border of the trapezius. Inferior (base).— middle third of the clavicle. The apex is at the superior nuchal of the occipital bone, where the sterno-mastoid and trapezius may n but the apex is usually truncated. The roof is formed by the ; superficial and deep fasciae, and for a short distance interiorly by platysma. The lesser occipital nerve lies in the upper part of roof, and the descending superficial branches of the cervical pi and the external jugular vein lie in the lower part of the roof, floor is formed by the following muscles, in order from above dc wards: (1) small angle of the semispinalis capitis, provided the trapt


is not well developed at the occiput; (2) the splenius capitis; (3) levator scapulae; (4) the scalenus medius and scalenus poster (5) the scalenus anterior; and (6) the first digitation of the sern anterior if the clavicle is depressed.

The posterior triangle is subdivided by the inferior belly of omo-hyoid into a large upper portion, called the occipital trian and a small lower portion, called the subclavian triangle.

Occipital Triangle—Boundaries — Anterior .—The posterior boi of the sterno-mastoid. Posterior .—The anterior border of trapezius. Inferior (base). —The inferior belly of the omo-hy The muscles in its floor are (1) a small angle of the semispinalis caj




THE HEAD AND NECK


1185

instant), (2) splenius capitis, (3) levator scapulae, and (4) scalenus .ius and posterior. The contents are the superficial branches of the ical plexus, the accessory nerve, the branches of the cervical

us to the levator scapulae and trapezius, a small part of the occipital

ry close to the apex, and some superficial cervical lymph glands.

t should be realized that the foregoing gives a picture of the triangle as seen le dissected body. In life and in the undissected part it is little more than tter, the anterior edge of the trapezius being only about \ inch from the srior border of the sterno-mastoid.


Parotid Duct Buccinator Muscle

Facial Artery Submental Artery


Lingual Artery Sup. Lar. Art. and Nerve Thyro-hyoid Muscle Superior Thyroid Artery


.Transverse Facial Artery


, Superficial Temporal Artery

- Maxillary Artery

/_Posterior Auriculat

wma ^ . Artery

Occipital Artery


-Stylo-hyoid Muscle

-Post. Belly of Digastric

-Hypoglossal Nerve

_Descendens Hypogloss'

_External Carotid

Artery


-Sterno-mastoid

.— w Trapezius


_Transverse Cervical Artery

-. Suprascapular Artery


Inf. Belly of Omo-hyoid

Subclavian Artery (third part)


, y 1, An

Fig. 711.—The Left Side of the Head and Neck. The platysma has been removed.


Cervical Plexus. —The cervical plexus lies deep to the upper part

he sterno-mastoid muscle, and immediately in front of the slips

•rigin of the scalenus medius. It is formed by the anterior primary ii of the first three cervical nerves and the greater part of that of fourth, a small branch of the latter descending to join the anterior nary ramus of the fifth, and so taking part in the brachial plexus, h of the anterior primary rami of the first four cervical nerves is nected with the superior cervical ganglion of the sympathetic by 'ey ramus communicans.


75








1186 A MANUAL OF ANATOMY

The anterior primary ramus of the first cervical nerve lies at f in the vertebrarterial groove of the atlas below the vertebral arte It then passes forwards in a groove on the outer surface of the supei articular process of the atlas, having the vertebral artery on its or side. It next emerges between the rectus capitis lateralis mu; (to which it gives a branch) and the rectus capitis anterior, ; descends in front of the root of the lateral mass of the atlas to join ascending branch of the second nerve. From the loop so forr


Vagus


Lesser Occip. N.


N.toTh

Int. La

Ne


Accessory Nerve ..


Ext. Li Nerv


Descent Hvpog Desc. C


Ansa


Ant. Jv


Fig. 712.—Deep Relations of Sterno-mastoid, showing Cervical

Plexus, etc.


branches are given to the rectus capitis anterior and the longus cap muscles, and one or more branches pass to the hypoglossal nerve, destination of their fibres being the ramus descendens cervicalis 2 the nerves to thyro-hyoid and genio-hyoid.

The anterior primary rami of the second, third, and fourth cervi nerves, having emerged between the corresponding intertransversa muscles, form a superficial and a deep part of the plexus, of wh the superficial is altogether cutaneous, while the deep is divided h


Phrenic


Upper Cord of Brachial Plexus








THE HEAD AND NECK


1187


tor and communicating branches. It will also be found that the p plexus consists of an external and an internal set of branches. Superficial Group. —The branches of this group are ascending, nsverse, and descending.

The ascending and transverse branches arise from the second and

d cervical nerves.

The ascending nerves are the lesser occipital and great auricular

p. 1141). The transverse branch is the anterior cutaneous nerve
he neck.

The anterior cutaneous nerve of the neck (superficial cervical nerve)

es by two roots from the anterior primary rami of the second and


Fig. 713. —Scheme of Cervical Plexus. superficial plexus red ; deep plexus black. I., E., medial and^lateral sides.


'rd cervical nerves, and, turning round the posterior border of the Tno-mastoid muscle, it passes forwards superficial to that muscle, ng deep to the platysma and the external jugular vein. Having iched the anterior triangle of the neck, it divides into two branches,

ending and descending, which are distributed to the integument

er the anterior triangle. The offsets of the ascending branch commicate freely with the cervical branch of the facial nerve deep to the itysma.

The descending branches are the medial, intermediate, and lateral 3 raclavicular nerves, and they arise in common from the third and irth cervical nerves. As they descend they form distinct nerves,






n88


A MANUAL OF ANATOMY


which lie on the roof of the subclavian triangle under cover of t platysma. For their distribution see p. 412.

Deep Group. —The nerves of this group are arranged in two sets external and internal.

External Set .—These nerves are muscular. The second ner furnishes a branch to the sterno-mastoid, which communicates in tb muscle with the branch of the accessory nerve. The third and four


Fig. 714. —Superficial Branches of Cervical Plexus.

SO, lesser occipital; GA, greater auricular; TC, anterior cutaneous; DC, descending supraclavicular; XI, accessory nerve.


nerves furnish (a) two branches to the trapezius, which communicc with the accessory nerve deep to the upper part of the muscle formi the subtrapezial plexus; ( b) two branches to the levator scapulae; a (c) branches to the scalenus medius.

Internal Set .—The nerves of this set are communicating a muscular.

The communicating branches are as follows: (1) connecting brand (grey rami communicantes) pass from the superior cervical gangli










THE HEAD AND NECK


1189


the sympathetic; (2) communicating branches pass to the vagus d hypoglossal nerves from the highest loop of the plexus; and two rami communicantes cervicales pass from the second and third rves forwards and downwards, usually superficial, but sometimes ep to the internal jugular vein, and join the descendens hypoglossi, aether or separately, to form the ansa hypoglossi.

The muscular branches are distributed to the rectus capitis lateralis,

tus capitis anterior and longus capitis, upper part of the scalenus

terior, longus cervicis, and the diaphragm. The nerve to the iphragm is the phrenic, which, from its importance, requires a special scription.

The phrenic nerve arises, as a rule, by two roots, the larger of lich is derived from the anterior primary ramus of the fourth cervical rve, and the other from that of the third. In some cases the fifth rvical nerve, which enters into the brachial plexus, furnishes an ditional small root. In the neck the nerve descends in front of the ilenus anterior muscle, which it crosses obliquely downwards and wards, passing deep to the intermediate tendon of the omo-hyoid uscle, the transverse cervical and suprascapular arteries, the anterior gular vein, and, on the left side, the thoracic duct. At the root of e neck the nerve, having left the scalenus anterior, passes behind e terminal part of the subclavian vein, and crosses in front of the ternal mammary artery from without inwards. Having come into ntact with the inner surface of the cupola of the pleura, it disappears kind the inner end of the clavicle, and enters upon the thoracic part its course (see p. 1015).

The right nerve at the root of the neck is superficial to the second irt of the right subclavian artery, with the intervention of the alenus anterior muscle. The left nerve at the root of the neck is iterior and parallel to the first part of the left subclavian artery.

The phrenic nerve is sometimes reinforced towards the root of the ick by a branch from the nerve to the subclavius muscle, and when is takes place the root from the fifth cervical nerve is usually absent, efore leaving the neck the phrenic nerve receives a twig from the iddle or inferior cervical ganglion of the sympathetic.

No branches arise from the phrenic nerve in the neck.

Lower Group of Deep Cervical Lymph Glands (Supraclavicular pmph Glands). —These glands lie in the anterior part of the subclavian iangle, and are related superficially to the intermediate supraclavicular 'rve and deeply to the upper and middle trunks of the brachial plexus. 'iperiorly they are continuous with the upper deep cervical lymph ands. They receive their afferent vessels from the following sources:

1. The back of the neck.

2. The axillary lymph glands.

3. The upper part of the pectoral region.

4. Occasionally the lymphatics along the cephalic vein, which ay ascend over the clavicle.

5- The internal mammary lymph glands.



1190


A MANUAL OF ANATOMY


Their efferent vessels form the subclavian trunk, which, with t jugular trunk, opens into the thoracic, or into the right lymphai duct.

Subclavian or Supraclavicular Triangle. —The subclavian triangle the lower division of the posterior triangle of the neck, and is separate from the upper division or occipital triangle by the inferior belly


Fig. 715. —Common Carotid and Subclavian Arteries exposed by Remow of Sterno-mastoid, Omo-hyoid, and Internal Jugular Vein.

the omo-hyoid muscle. Situated above the middle third of the clavicl* it is of small size until the deep cervical fascia, which ensheathes tt inferior belly of the omo-hyoid, has been divided.

Boundaries — Superior .—The inferior belly of the omo-hyoid muscf Inferior .—The middle third of the clavicle. Anterior .—The clavicuk part of the sterno-mastoid muscle. Roof .—The skin; superficial fasci










THE HEAD AND NECK


1191


platysma muscle; medial, intermediate, and lateral supraclavicular es; a part of the external jugular vein; and the deep cervical fascia, if.—The scalenus medius and posterior muscles, and the serratus

rior.

rhe extent of the triangle is affected by (T) the height to which inferior belly of the omo-hyoid ascends above the clavicle, and the extent of the clavicular attachments of the sterno-mastoid trapezius muscles. The depth of the triangle is influenced by the tion of the shoulder, being greater when the shoulder is raised carried forwards, and less when it is depressed and carried kwards.

Contents. —The contents are: (1) the greater portion of the third t of the subclavian artery; (2) small portions of the transverse


Brachial Plexus Cephalic Vein Musculo-cutaneous Nerve Deltoid


Trapezius

1 Suprascapular Vessels

\ Transverse Cervical Artery

Inferior Belly of Omo-hyoid

Scalenus Anterior / Sterno-mastoid


-Clavicle in section


Subclavius


Axillary Artery - Axillary Vein

Pectoralis Major (cut)


Pec!oralis Minor Lateral Root of Median Nerve


Medial Cutaneous Nerve of Arm

Axillary Vein

Ulnar Nerve


Medial Root of Median Nerve Medial Cutaneous Nerve of Forearm


Fig. 716. —Subclavian and Axillary Regions.


vical artery and vein; (3) the lower portion of the external jugular in; (4) the nerve-trunks of the brachial plexus; and (5) the nerve the subclavius muscle, the suprascapular nerve, and the nerve serratus anterior

Third Part of the Subclavian Artery. —1 his part of the vessel extends >m the outer border of the scalenus anterior muscle to the outer rder of the first rib, where it becomes the axillaiy artery. Its course downwards and outwards, and for the greater part of its extent it s in the subclavian triangle. Its last inch or so, howevei, passes

hind the clavicle and subclavius muscle.

Relations- — Anterior .—The skin; superficial fascia and platysma; edial, intermediate, and lateral supraclavicular nerves; deep cervical >cia; clavicle and subclavius muscle; transverse cervical vessels; prascapular vessels; nerve to the subclavius muscle; and the termina





1192


A MANUAL OF ANATOMY


portion of the external jugular vein. The last-named vessel cro: in front of the artery close to the sterno-mastoid muscle, and in ■ situation is joined by the transverse cervical and suprascapular ve A plexiform arrangement of veins is sometimes met with in from the artery, which may be rendered more complex by a branch ascenc superficial to the clavicle from the cephalic vein. Posterior .—' scalenus medius, the lower nerve-trunk of the brachial plexus in vening. Superior .—The upper and middle nerve-trunks of the brad plexus, the latter being nearest the vessel. Inferior .—The upper s face of the first rib and the subclavian vein, the vein being on a m anterior plane than the artery, and lying behind the clavicle.

It is most important to understand that, though the first rib is spoken o an inferior relation, its surface is so oblique that it is just as much behinc below.

The third part of the subclavian artery does not always give any branch. In very many cases, however, the deep branch of transverse cervical artery arises from it, instead of from the latter arte

which is a branch of the first, p of the subclavian. In these ca the posterior scapular art passes outwards between nerve - trunks of the brad plexus.

The direction of the third p of the artery is indicated b^ line drawn from a point on i posterior border of the ster mastoid muscle, about J ir above the clavicle, to the cen of that bone. The artery may compressed as it passes over 1 first rib, the guide to it at t point being the centre of i clavicle. In order to tie the si clavian artery in the dead bo< after fully depressing the clavi( feel for the outer edge of the scalenus anterior muscle, and follow to its insertion on the first rib. The structure which lies immediat behind the muscle here is the artery; and great care must be taken i to mistake it for the lower trunk of the brachial plexus.

For the manner in which the collateral circulation is carried after ligation of the third part of the subclavian artery, see p. 441.

The subclavian vein, in the region of the subclavian triangle, situated behind the clavicle, where it lies below and anterior to 1 artery. On the upper surface of the first rib it is anterior to the scaler anterior, and it receives the external jugular vein, and in some ca the anterior jugular vein,


Fig. 717.— Plan of Branches of Subclavian Artery.



THE HEAD AND NECK


ii 93


L'he transverse cervical artery lies in the subclavian triangle for Lort distance only, close to where the inferior belly of the omoid passes deep to the sterno-mastoid. It passes outwards behind former muscle into the lower part of the occipital triangle, where ivides into its superficial and deep branches, the former entering trapezius, and the latter passing in front of the levator scapulae, r which it descends along the base of the scapula in front of the nboid muscles.

rhe transverse cervical vein opens into the external jugular vein, •e being a valve at or near its ending.

rhe suprascapular artery is not in the subclavian triangle, but lies ind the clavicle, close to its upper aspect. It will be described in nection with the first part of the subclavian artery (see p. 1243).

The suprascapular vein also lies behind the clavicle, and it opens > the external jugular vein, there being a valve at or near its ending. The external jugular vein will be found described on p. 1176.

Brachial Plexus. —The brachial plexus is situated in the lower part he posterior triangle of the neck, behind the clavicle, and in the >er part of the axilla. Its complex formation is rendered simple arranging it into four stages—namely (1) nerve-roots, (2) nervenks, (3) divisions of nerve-trunks, and (4) nerve-cords.

First Stage .—The nerves which form the plexus are the anterior nary rami of the fifth, sixth, seventh, and eighth cervical, and the ater part of that of the first thoracic. Superiorly the plexus is lforced by a small descending branch from the fourth cervical, ich joins the fifth, and interiorly it is occasionally reinforced by a ,nch from the second thoracic, which joins the first. As regards the t thoracic nerve, the part of it which does not join the plexus, and ich is of small size, enters the first intercostal space to become the t intercostal nerve. The nerves, as thej^ emerge at the side of the k, are placed between the scalenus anterior and scalenus medius, which they give branches.

Second Stage .—The fifth and sixth cervical nerves join at the

er border of the scalenus anterior to form the upper trunk ; the

r enth cervical remains meanwhile single, and forms the middle nk ; and the eighth cervical and greater part of the first thoracic ite between the scalene muscles to form the lower trunk. There ! thus three trunks—upper, middle, and lower.

Third Stage.—A little above the clavicle each of the three trunks ^aks up into anterior and posterior divisions.

Fourth Stage.— The anterior divisions of the upper and middle inks unite to form the lateral cord of the plexus; the anterior dsion of the lower trunk, which is of large size, forms the medial rd; and all three posterior divisions (that of the lower trunk being small size) unite to form the posterior cord. There are thus three rds—lateral, medial, and posterior. As a variety, the anterior /ision of the middle trunk may subdivide into two branches, one tering the lateral cord and the other the medial.


H 94


A MANUAL OF ANATOMY


Branches of the Plexus above the Clavicle. —The branches are c< veniently divided into two groups—supraclavicular, arising above 1 clavicle, and coming from nerve-roots and nerve-trunks; and inf clavicular, arising below the clavicle, and coming from nerve-cords.

Supraclavicular Branches .—These are muscular branches fr< the four cervical nerves to the scalene muscles and longus cervicis.

One root of the phrenic nerve (inconstant) from the front of 1 fifth cervical.

The Nerve to the Rhomboids. —This branch arises from the ba of the fifth cervical, close to or along with the highest root of 1


Iug. 718. —The Brachial Plexus.

\ ellow=spinal nerves and their branches; blue=trunks; red=lateral cord

purple=medial cord; grey=posterior cord.

neive to serratus anterior, and it takes a backward course throu the scalenus medius.

The Nerve to the Serratus Anterior (Nerve of Bell or Posteri Thoracic Nerve). —This branch arises by three roots from the ba of the fifth, sixth, and seventh cervical nerves. The upper two ro( pierce the scalenus medius muscle below the nerve to the rhomboi( either conjointly or separately, whilst the lowest root passes in fro of the scalenus medius, and joins the trunk formed by the oth( neai the first rib. The nerve then courses behind the brachial plex and the first part of the axillary artery to the axillary surface of t serratus anterior, which it supplies.



THE HEAD AND NECK


ii95


he Nerve to the Subclavius. —This small branch arises from the of the upper trunk, its fibres being derived from the fifth cer. It descends in front of the third part of the subclavian artery, passing behind the clavicle, enters the subclavius muscle on leep aspect. This nerve sometimes communicates with the nic nerve.

he Suprascapular Nerve. —This is a large nerve which arises from Dack of the upper trunk, its fibres being derived from the fifth


Fig. 719. —Plan of Triangles of Neck.

sixth cervical. It is directed downwards, outwards, and backds beneath the trapezius and inferior belly of the omo-hyoid to upper border of the scapula, on approaching which it meets the rascapular artery. It is distributed to the supraspinatus and ispinatus muscles and shoulder-joint.

[t will be seen that all the branches of the brachial plexus belong er to the anterior or posterior divisions, even if they come off before >e divisions become separate, and that their distribution gives a clue






1196


A MANUAL OF ANATOMY


to the division to which they belong. The nerves to the scale] medius and posterior, as well as that to the rhomboids, the sup scapular, and to serratus anterior, are, from their distribution, clea dorsal or posterior in their origin; while the nerves to the scale] anterior, longus cervicis, and subclavius are equally clearly anteric

Below the clavicle the lateral and medial cords give off all the antei branches, while the posterior come entirely from the posterior cord.

For the infraclavicular branches of the brachial plexus, see p. 4

Anterior Triangle. —This triangle is situated in front of the ster: mastoid muscle, and its base is directed upwards.

Boundaries — Anterior. —The middle line of the neck—that is say, a line extending from the chin to the upper border of the mai brium sterni. Posterior. —The anterior border of the sterno-mast muscle. Superior. —The lower border of the mandible and a 1 drawn from the angle of that bone to the mastoid process. 1 triangle is covered by the skin, superficial cervical fascia, platysr and deep cervical fascia. Superficial to the deep fascia there the following structures: the anterior jugular vein, the ramificati< of the anterior cutaneous nerve of neck, and the cervical branch of 1 facial nerve.

The anterior triangle is subdivided into three triangles by i superior belly of the omo-hyoid muscle inferiorly, and posterior be of the digastric muscle superiorly. The subdivisions from bel upwards are called muscular, carotid, and submandibular.

The muscular triangle is bounded anteriorly by the middle line the neck; posteriorly by the anterior border of the sterno-mastoid; a superiorly by the superior belly of the omo-hyoid.

The carotid triangle is bounded inferiorly by the superior be of the omo-hyoid; superiorly by the posterior belly of the digast and stylo-hyoid; and posteriorly by the anterior border of the sten mastoid.

The submandibular triangle (submaxillary triangle) is bound

postero-inferiorly by the lower part of the posterior belly of the digasti the stylo-hyoid, and by the body of the hyoid bone: antero-inferio by the mid-line of the neck; and superiorly by one half of the be of the mandible, and a line drawn from the angle of that bone to t sterno-mastoid muscle.

Contents of the Triangles—Muscular Triangle (Fig. 719).—The ai of this triangle is occupied by the sterno-hyoid and sterno-thyn muscles; hence the name muscular triangle. Under cover of th< muscles there are the carotid sheath with its contents, the late lobe of the thyroid gland, the trachea, and the larynx. The oesophag lies behind the trachea, with a slight inclination towards the 1 side at the root of the neck, and the recurrent laryngeal nerve 1 in the groove between the trachea and the oesophagus. The infer thyroid artery has a tortuous course inwards behind the lower p; of the carotid sheath, and the trunk of the sympathetic descer behind both.




THE HEAD AND NECK


1197


arotid Triangle. —This triangle contains the upper part of the non carotid, and the beginnings of the external and internal

id arteries, all of which are overlapped by the anterior border

le sterno-mastoid, when the connective tissue which ensheathes muscle is undisturbed. The common carotid and internal carotid ies, together with the vagus nerve, are contained within the tid sheath, and the descendens hypoglossi lies in front of the th, or within it, being situated in either case in front of the common tid artery. The sterno-mastoid artery and the superior thyroid cross the sheath near the bifurcation of the common carotid


.Transverse Facial Artery


Parotid Duct -Buccinator Muscle Facial Artery -Submental Artery


Lingual Artery — Sup. Lar. Art. and Nerve Thyro-hyoid Muscle _. Superior Thyroid Artery


Inf. Belly of Omo-hyoid-,

Subclavian Artery (third part)


, Superficial Temporal Artery

HPI"' Maxillary Artery

Posterior Auriculav

r Artery

/r _ Occipital Artery

>itW

,,,, . .-. - JIlifL. _Stylo-hyoid Muscle

WyMSm---- Post - Bel, y of Di s astric

!£- _Hypoglossal Nerve

-Descendens Hypoglossi

Jj_External Carotid Artery


-Sterno-mastoid

Trapezius

_Transverse Cervical Artery

_. Suprascapular f\ Artery


^iwii iin^wiu !ii wu M1 1 \w ' An '

Fig. 720.—The Left Side of the Head and Neck. The platysma myoides has been removed.


  • ry, and the carotid body lies behind the vessel about the same

d. The deep cervical lymph glands lie just lateral to the course he internal jugular vein. The origins of the superior thyroid, lingual, ial, and occipital arteries are contained in this triangle, and the ending pharyngeal branch of the external carotid lies deeply between t vessel and the internal carotid. The internal jugular vein in this ingle receives the common facial, lingual, and superior thyroid veins, e hypoglossal nerve lies along the lower border of the posterioi ly of the digastric muscle, and it here gives off, fiom behind wards, the descendens hypoglossi and the nerves to thyio-hyoid









A MANUAL OF ANATOMY


1198


and genio-hyoid, the former passing downwards in front of, or witl the carotid sheath, and the latter passing forwards and downwards an acute angle with the parent trunk. The internal branch of superior laryngeal nerve lies deeply behind the bloodvessels, and external laryngeal branch of that nerve descends parallel and deep the superior thyroid artery, and passes deep to the upper end of posterior border of the sterno-thyroid muscle. The vagus nerve within the carotid sheath, and the sympathetic trunk is behind The accessory nerve lies deeply, its course being downwards and ba wards beneath the sterno-mastoid, the deep portion of which usual! pierces about an inch below the angle of the mandible.

Digastric Triangle.—This triangle is divided into two parts, antei and posterior, by the stylo-mandibular ligament. The anterior p contains the superficial part of the submandibular gland, the antei facial vein being superficial to it, and the facial artery being embed( in its upper and back part. In this triangle the facial artery gives its ascending palatine, tonsillar, glandular, and submental brand The muscles in the floor of the anterior part of the triangle are mylo-hyoid and a part of the hyo-glossus. The superficial part of submandibular gland is superficial to the mylo-hyoid muscle, a conceals the mylo-hyoid nerve and submental artery, which are direct contact with the muscle. The hypoglossal nerve lies upon t] part of the hyo-glossus muscle which appears in the anterior part the triangle, but it soon disappears beneath the posterior free bon of the mylo-hyoid muscle. It is important to notice that it lies para to and just above the greater horn of the hyoid bone, which forms important structure in the floor of the triangle, and shows a little the insertion of the thyro-hyoid muscle below it.

The anterior jugular vein and the anterior cutaneous nerve of 1 neck have been already described (see pp. /1173 and 1187). 1 cervical branch of the facial nerve will be found described on p. 12

Submandibular Lymph Glands (Submaxillary Lymphatic Glands) These glands lie upon the superficial surface of the submandibu salivary gland, under cover of the deep cervical fascia. They forn chain beneath the corresponding half of the base of the mandit which extends from near the angle of the bone to near the origin of 1 anterior belly of the digastric muscle. The central gland of the chi is closely related to the facial artery as that vessel is about to asce


over the base of the mandible, from the following sources:

1. The front of the scalp.

2. The side of the nose.

3. A few from the lower eyelid.

4. The lower part of the cheek.

5. Half of the upper lip.

6. The lateral part of the lower lip

7. The anterior third of the lat eral border of the tongue.


They receive their afferent vess


8.


9 10.


11.

12.


The subjacent portion of floor of the mouth.

Half of the upper gum.

The lateral part of the lo^ gum.

The facial lymph glands.

The submandibular and si lingual salivary glands.


THE HEAD AND NECK


1199


Their efferent vessels pass to the upper deep cervical lymph glands, ch are on a level with the upper border of the thyroid cartilage of larynx.

The submental lymph glands lie beneath the chin, and are two or

e in number. They receive their afferent lymphatics from the tip

he tongue, the front of the floor of the mouth, and the inner part the lower lip; and their efferent lymphatics pass to the subidibular lymphatic glands. It must be borne in mind that these Lphatic vessels, like those elsewhere in the body, frequently comnicate across the middle line.

The prelaryngeal lymph glands, when present, are situated in front the crico-thyroid ligament, and are one or two in number. They give their afferent lymphatics from the interior of the larynx, dw the rima glottidis, and from the adjacent part of the thyroid nd. Their efferent lymphatics pass to the inferior deep cervical lph glands. The upper part of the larynx drains into the superior p cervical lymph glands along a course accompanying that of the >erior laryngeal vessels.

The para- and pretracheal lymph glands lie in front and at the sides the trachea, from which, as well as from the adjacent part of the a*oid gland, they receive their afferent lymphatics. Their efferent iphatics pass to the inferior deep cervical lymph glands. Occasionally a few lymph glands are met with along the course the anterior jugular vein.

Deep Cervical Lymph Glands. —These glands lie deep to the sternostoid muscle, and are very numerous. They are arranged in two tups, superior and inferior.

The superior deep cervical lymph glands lie along the internal

ular vein above the level of the upper border of the thyroid cartilage,

ey receive their afferent lymphatics from the cranial cavity, the ernal maxillary glands, some of the parotid and submandibular nph glands, the root of the tongue, the upper part of the thyroid nd, the upper part of the larynx, and the lower part of the pharynx, eir efferent lymphatics pass to the inferior deep cervical lymph nds. One large gland of this group is very constant, and lies close the angle of the mandible. It drains the dorsum and sides of the igue, but not the tip as a rule.

The inferior deep cervical lymph glands lie along the lower part of j internal jugular vein, and extend outwards and backwards deep to

1 sterno-mastoid as far as its posterior border. These lymph glands J continuous inferiorly with the deep cervical lymph glands lying the subclavian triangle, and, through these, with the axillary glands, ey receive their afferent lymphatics from the superior deep cervical nph glands, the upper superficial cervical lymph glands, the lower rt of the thyroid gland and larynx, and the cervical portions of the ichea and oesophagus. Their efferent lymphatics unite to form a ^gle vessel, called the jugular trunk, which opens on the left side into

2 thoracic duct, and on the right side into the right lymphatic duct.


1200


A MANUAL OF ANATOMY


Infrahyoid Muscles. —These are the omo-hyoid, sterno-hyoi sterno-thyroid, and thyro-hyoid.

Omo-hyoid. —This muscle consists of two bellies, superior (anteric and inferior (posterior), and an intermediate tendon. Origin .—I means of the inferior belly from (i) the upper border of the scapu close to the inner side of the suprascapular notch, and (2) the supr scapular ligament, which bridges over the suprascapular notch.

Insertion .—By means of the superior belly into the outer third the lower border of the body of the hyoid bone immediately later to the insertion of the sterno-hyoid muscle.

Nerve-supply .—The superior belly is supplied by the ramus desce dens hypoglossi, and the posterior belly derives its branches from t] ansa hypoglossi.


Greater Horn


Lesser Horn


Omo-hyoid (Sup. Belly)


1


Fig. 721.—The Hyoid Bone, showing its Muscular Attachments.

The inferior belly is contained in the posterior triangle of the nec and separates the occipital from the subclavian triangle. Its course forwards and slightly upwards, and it passes deep to the stern mastoid muscle, where its fibres terminate in the intermediate tendo It is ensheathed by a deep process of the deep cervical fascia as th fascia crosses the posterior triangle, and this process is attached to t back of the inner end of the clavicle and the first rib, which explai the almost horizontal position occupied by the inferior belly.

The superior belly proceeds from the intermediate tendon, ai passes upwards and slightly inwards to the body of the hyoid bor As it emerges from beneath the anterior border of the sterno-mastc muscle the superior belly crosses the carotid sheath on a level wi the narrow anterior part of the cricoid cartilage, and in the anteri triangle of the neck it forms the separation between the muscular ai carotid triangles.




THE HEAD AND NECK


1201


rno-hyoid — Origin. —(i) The posterior surface of the manubrium at its upper and outer part; (2) the posterior sterno-clavicular jnt; and, sometimes, (3) the posterior surface of the clavicle at Ler end.

sertion. —The inner two-thirds of the lower border of the body of roid bone, extending from the middle line to the insertion of the or belly of the omo-hyoid. irve-supply. —The ansa hypoglossi.

ie muscle is flat and ribbon-like, and rests upon the sternod and thyro-hyoid.

irno-thyroid — Origin. —(r) The posterior surface of the manusterni at its upper and outer part below the origin of the sterno; and (2) the posterior surface of the first costal cartilage. sertion. —The oblique line on the -outer surface of the lamina of Lyroid cartilage.

irve-supply. —The ansa hypoglossi. The nerves enter this and st muscle quite at the lower part of the neck, ie muscle is broader, but shorter, than the sterno-hyoid underwhich it lies. Within the thorax the right muscle lies in front 3 innominate artery, and the left in front of the left common d artery and left innominate vein. In the neck each muscle upon the carotid sheath and the corresponding right or left lobe 5 thyroid gland.

ie sterno-hyoid muscles as they leave the thorax are separated 1 interval, in which situation the sterno-thyroid muscles lie in contact. As the muscles ascend the sterno-hyoids converge, but erno-thyroids diverge.

tyro-hyoid — Origin. —The oblique line on the outer surface of tmina of the thyroid cartilage.

\sertion. —(1) The outer half of the lower border of the body of yoid bone; and (2) the basal half of the greater horn of that

erve-supply. —A special branch of the hypoglossal, though originlerived from the first and second cervical nerves. The nerve 3 the surface of the muscle close to its posterior border, ie muscle is quadrilateral. Its superficial surface supports the ior belly of the omo-hyoid and the sterno-hyoid muscles, and its surface is related to the lamina of the thyroid cartilage, the -hyoid membrane, the internal branch of the superior laryngeal

, and the superior laryngeal artery.

e nerves which supply the infrahyoid group of muscles are derived from 'st, second, and third cervicals through the hypoglossal and ansa hypo ction of the Infrahyoid Muscles — Omo-hyoid. —(1) lo depress yoid bone; and (2) to render tense the deep cervical fascia in the part of the neck.

erno-hyoid. —To depress the hyoid bone, erno-thyroid. —To depress the thyroid cartilage.


76



1202


A MANUAL OF ANATOMY


Thyro-hyoid.— (i) To depress the hyoid bone; and (2) to ele the thyroid cartilage, as in the production of high notes, or in glutition.

Structures in the Median Line of the Neck. —The median line of neck is divisible into two regions, suprahyoid and infrahyoid.

Suprahyoid Region. —The innermost fibres of the two platy muscles decussate at the median line for a short distance below chin. On either side of the median line, under cover of the platy< is the anterior belly of the digastric muscle. The anterior bellic


Posterior Belly of Digastric— and Stylo-hyoid Hyo-glossus Muscle and Hypoglossal Nerve


Ster. Head of St.-mas. -Crico-thyroid Muscle -

Cricoid Cartilage Lat. Lobe of Thyroid Gland

Trapezius

Clavicular Head of Stemo-mastoid Brachial Plexus


Subclavian Artery (third part)

Clavicle


Anterior 'Belly of Diga: jf Mylo-hyoid


Body of Hyoid Bone _ Superior Belly of Omo ' - Stemo-hyoid


Thyro-hyoid


Thyroid Cartilage Sterno-thyroid Superior Belly of Omo Crico-thyroid Ligamen


Stemo-hyoid


Isthmus of Thyr Gland


■s Inferior Thyroid y of Veins

Cla. Head of St.-i


,T\T

-\r Sterno-thyroid


Sternal Head of Sternomastoid


Sterno-thyroid


Sterno-hyoid


Fig. 722.—Dissection of the Front of the Neck.

The area bounded on either side by the anterior belly of the digastric a below by the body of the hyoid bone is the submental triangle.


opposite sides are near each other at the chin, but as they des< with an inclination outwards they diverge from each other, and 1 between them a triangular interval sometimes called the subm< triangle. The base of this triangle is formed by the body of the h bone, and each lateral boundary is constructed by the anterior 1 of the digastric, the apex being placed at the chin. The area oi triangle is occupied by the anterior portions of the mylo-hyoid mus which meet at the median line in a tendinous raphe, and super! to these muscles there are the submental lymph glands.


















THE HEAD AND NECK


1203


Epiglottis


Greater Horn of Hyoid Bone~

Lesser Horn of Hyoid Bone Body of Hyoid Bone-"

Thyro-hyoid Membrane -Levator (Mandril® ) Thyroid® Muscle / Thyroid Cartilage - Crico-thyroid Ligament. Pyramidal LobeCricoid Cartilage'

Right Lobe of Thyroid Gland Isthmus


Trachea


lubmental Lymph Glands. —These glands, usually two in number,

1 the submental triangle beneath the chin and above the body of hyoid bone, one being on either side of the median line. Each d receives its afferent vessels from (1) the medial portions of the

r lip and lower gum; (2) the tip of the tongue and adjacent portion

le floor of the mouth; (3) the skin of the chin; and (4) sometimes upper lip. Their efferent vessels pass to (1) the submandibular ph glands, and (2) the ilo-omo-hyoid lymph gland, of the superior deep cer 1 lymph glands, infrahyoid Region. —The re from the hyoid bone downis to the suprasternal notch the upper border of the Lubrium sterni is of conrable importance in conion with bronchocele or re, laryngotomy, and traDtomy.

The body of the hyoid bone

r well-marked structure, lg with the greater horn on er side of it. Below the id bone there is the thyroid membrane, which passes /ards within the lower borof the hyoid bone. The t structure is the thyroid kilage, the upper border of ch has a well - marked iian notch, whilst its two form by their union the minent laryngeal prominence mum Adami).

Succeeding the thyroid carti 2 there is a narrow interval, which is occupied by the crico-thyroid iment, and immediately below this is the narrow anterior part of

cricoid cartilage. The crico-thyroid ligament is only exposed close the median line, being elsewhere covered by the two crico-thyroid scles. The exposed part of the ligament is crossed by the cricovoid arterial arch, which is situated midway between the thyroid 1 cricoid cartilages, and lying upon the ligament there may be i or two prelaryngeal lymphatic glands. Laryngotomy may be formed in the crico-thyroid region, and the crico-thyroid arterial h has to be borne in mind.

Succeeding the cricoid cartilage is the trachea, which, as it cends, inclines backwards, and therefore becomes somewhat


Right Bronchus^ Eparterial Bronchus, Hyparterial Bronchus.^'


Si'- ; .

err::.?*,

iCZZZv

.

^ ".."..-A


Left Bronchus

Fig. 723. —The Hyoid Bone, Larynx Trachea, Bronchi, and Thyroid Gland (Anterior View).












1204


A MANUAL OF ANATOMY


inaccessible; at the suprasternal notch it may be i£ inches fr the surface. The thyroid gland is intimately related to it superioi Each lobe closely embraces it laterally as low as about the fifth ri and the isthmus lies in front of the second and third rings as a n but its position is liable to variation. Crossing the upper border of isthmus there is one of the branches of the superior thyroid arte known as the artery of the isthmus.

There is nothing of any importance in front of the trachea ab< the isthmus of the thyroid gland. Below the isthmus there is a m or less copious plexus of veins, called the inferior thyroid plexus, fr which the right and left inferior thyroid veins descend. OccasI ally a small artery, called the arteria thyroidea ima, ascends direc in front of this part of the trachea in the median line to reach i


\c



% \


\ \ \ » / / / / / —V-A-A-/ / /


phrenic ru-^ scalenus anterior'--., thyro-cervical trunk—-.

sub'elcw^ ay— scalenus medius—

vertebral vn.-vertebral ay.-


-vagus n. 'omo-hyoid

—brachial plexus

-I 5 - 1 rib

sympathetic trunk

Z n _d r jb


zura—"

oesophagus

long, cap. and long cer. disc, between 1st and 2nd thoracic vtb.


\2 n - d thoracic tr pr '"'I s - thoracic spinous pr


Fig. 724.—Section through Lower Part of Neck.


isthmus of the thyroid gland. The innominate, and even the rig common carotid, artery and the left innominate vein sometirr encroach upon the front of the trachea towards the root of the nec The latter is a particularly important arrangement to remember, a: occurs more frequently in women and children. In early life t upper part of the thymus covers the front of the trachea. The foi going structures are covered by the sterno-thyroid and sterno-hyc muscles in the following manner: the two sterno-thyroid muscles a in contact with each other for a short distance above the manubriri sterni, so as to cover the trachea, but the two sterno-hyoid muse! are here separated by an interval; superiorly the two sterno-thyre muscles diverge, and the two sterno-hyoid muscles come very near together.






THE HEAD AND NECK


1205


he operation performed upon the trachea is tracheotomy, rding as it is performed above or below the isthmus of the thyroid 1 , it is spoken of as the high or the low operation. In the high ition there is no anatomical obstacle, unless it be a close attach: of the isthmus of the thyroid gland to the tracheal rings which vers. In the low operation the following obstacles are present: he trachea is here less accessible, because it recedes from the ,ce; (2) the inferior thyroid plexus of veins might prove trouble


.Ansa


- Ant. Jug. V. Vagus


N. toThyro-hyoid

Int. Laryngeal Nerve


Ext. Laryngeal Nerve

Descendens Hypoglossi Desc. Cerv.


sser Occip. N. •


Upper Cord of rachial Plexus


cessory Nerve..


Phrenic

725.— Deep Nerves in the Neck in Relation with Carotid Sheath.


e; (3) an arteria thyroidea ima may be present; (4) the innominate right common carotid arteries and the left innominate vein may endangered; and (5) in young children the thymus would be in the

Fhe Ramus Descendens Hypoglossi (Descendens Cervicis Nerve).

ramus descendens arises from the hypoglossal nerve as the latter ks round the occipital artery, its fibres being derived from the municating branches which the hypoglossal receives from the loop





1206


A MANUAL OF ANATOMY


between the first and second cervical nerves. The nerve, whicl long, passes downwards and slightly forwards, lying upon, or witl the carotid sheath, and in either case directly over the line of common carotid artery. Before reaching the centre of the necl furnishes a branch to the superior belly of the omo-hyoid mus Lower down it is joined by a branch which is formed by the unior the two rami communicantes cervicales from the anterior primary r; of the second and third cervical nerves. These two rami, howe^ sometimes join it separately. In this manner a loop is formed usu; about the level of the cricoid cartilage, which is called the ansa hy


H.G.


Fig. 726.— Scheme of the Hypoglossal Nerve, showing its Connections with Cervical Spinal Nerves.

Sy., twig from sympathetic; Pn., communicating with vagus; ic, 2c, 3c, fi second, and third cervical; C.H., communicans hypoglossi; C.C., c< municantes cervicalis; D.C., descendens hypoglossi; A.B.O.H., to ante belly of omo-hyoid; A.C., ansa hypoglossi; S.H., to sterno-hyoid; S.T. sterno-thyroid; P.B.O.H., to inferior belly of omo-hyoid; T.H., to th] hyoid; G.H., to genio-hyoid; G.H.G., to genio-glossus; H.G., to hyo-gloss S.G., to stylo-glossus.

glossi. The convexity of the loop is directed downwards, and fr it branches are given off to (1) the sterno-hyoid, (2) the sterno-thyrc and (3) the inferior belly of the omo-hyoid muscles.

The fibres of the ramus descendens hyo-glossi are of spinal, not hypoglos; origin.

For the rami communicantes cervicales, see Cervical Plexus (p. ii£

The Nerve to Thyro-hyoid. —This nerve, which is composed of spf fibres derived from the loop between the first and second cervi nerves, arises from the hypoglossal at the lower border of the poster belly of the digastric. It passes forwards and downwards, formi


THE HEAD AND NECK


1207


ute angle with the parent trunk, and enters the thyro-hyoid

le on its superficial surface.

irotid Sheath. —The carotid sheath, already described on p. 1179, ived from the posterior lamina of the sheath of the sterno-mastoid le, and is intimately connected anteriorly with the pretracheal , and posteriorly with the prevertebral layer, of the deep cervical i The interior of the sheath is divided into three compartments— •, inner, and posterior. The outer and inner compartments are •ated from each other by a septum, the inner compartment containhe common carotid artery and, it may be, the ramus descendens glossi, and the outer compartment the internal jugular vein. The rior compartment is situated within the back part of the septum, contains the vagus nerve. The ramus descendens hypoglossi may pon the sheath, or within it, and the trunk of the sympathetic mds behind, and in intimate relation with it.

tie foregoing is the usual account of this sheath, but there are some anaits who believe that not only it, but many other fascial planes are hardly


Fig. 727.—Scheme of Section through Carotid Sheath showing

Contents and Certain Relations.


mizable in the living or in the undisturbed dead body In any case, there > reason to believe that the carotid has more or less of a sheath than any r artery of its own size elsewhere.

[Jommon Carotid Arteries— The right common carotid artery arises 1 the innominate artery behind the upper border of the right sternoicular joint, and the left common carotid aitery arises from the er surface of the arch of the aorta, in close proximity to the origin he innominate artery. The vessel of the right side is therefore rely cervical, whilst that of the left side is partly thoracic and part y

The thoracic part of the left common carotid artery has alieady n described in connection with the thorax (see p. 1039)In the neck the common carotid artery of each side extends from back of the corresponding sterno-clavicular joint to the level o upper border of the thyroid cartilage of the larynx, which corrends to the disc between the bodies of the third and fourth cervica tebrse. At this level the vessel divides into the external and interna



1208


A MANUAL OF ANATOMY


Fig. 728. —The Aorta in


1. Arch of the Aorta

2. Aortic Isthmus

3. Aortic Spindle

4. Descending Aorta

5. Coronary Arteries (from

Ascending Aorta)

6. Innominate Artery

7. Left Common Carotid

8. Left Subclavian

9. Right Common Carotid


the Thorax, and the Head and Neck.

10. Right Subclavian

11. External Carotid

12. Internal Carotid

13. Maxillary

14. Superficial Temporal

15. Vertebral

16. Internal Mammary

17. Thyro-cervical Trunk

18. Inferior Thyroid

19. Transverse Cervical


Principal Arteries of i


20. Suprascapular

21. Superior Thyroid

22. Lingual

23. Facial

24. Occipital

25. Posterior Auricular

26. Ascending Pharyngea

27. Transverse Facial

28. Posterior Intercostals

29. Ligamentum Arteriosum







THE HEAD AND NECK


1209


rotid arteries. The place of bifurcation is sometimes opposite the dy of the hyoid bone, and, more rarely, on a level with the cricoid rtilage of the larynx. The vessel is about 3J inches long, and its urse is upwards and outwards in the direction of a line drawn from 3 sterno-clavicular joint to a point midway between the angle of 3 mandible and the mastoid process of the temporal bone. This e, as high as the level of the upper border of the thyroid cartilage, Dresents the course of the common carotid artery. At the root of e neck the two common carotid arteries are not very far apart, and e trachea lies in the intervening space. As the two vessels ascend ey become more divergent, on account of the projection of the right d left lobes of the thyroid gland and the thyroid cartilage.

The artery, along with the internal jugular vein and vagus nerve, d, perhaps, the ramus descendens hypoglossi, is contained within e carotid sheath, already described. Opposite the cricoid cartilage is crossed by the superior belly of the omo-hyoid muscle. Below is level it lies deeply in the region of the muscular triangle, being Lder cover of the sterno-hyoid and sterno-thyroid muscles, in addition the platysma and the anterior border of the sterno-mastoid. Above is level it is situated in the carotid triangle, where it is more super:ially placed, its only muscular coverings being the platysma and the iterior border of the sterno-mastoid.

Relations — Anterior .—The skin; superficial fascia and platysma; vesting layer of the deep cervical fascia; anterior border of the erno-mastoid; sterno-hyoid; sterno-thyroid; superior belly of the no-hyoid; and the anterior wall of the carotid sheath. Three veins oss the artery from without inwards: (1) the anterior jugular vein osses it immediately above the clavicle, superficial to the sternoA>id and sterno-thyroid muscles; (2) the middle thyroid vein just jlow the level of the cricoid cartilage; and (3) the superior thyroid jin near its bifurcation. The sterno-mastoid branch of the superior lyroid artery, which is of small size, passes obliquely downwards id outwards in front of the carotid sheath in the carotid triangle, tie ramus descendens hypoglossi descends in front of the carotid Leath to form the ansa hypoglossi.

Posterior .—The posterior wall of the carotid sheath; the cervical ansverse processes as high as the level of the fourth; the longus irvicis, scalenus anterior, and part of the longus capitis muscles; ie sympathetic trunk, which is intimately related to the posterior all of the carotid sheath; the recurrent laryngeal nerve; and the iferior thyroid artery, both of which latter structures pass inwards id upwards behind the lower part of the sheath.

Lateral .—The internal jugular vein and the vagus nerve, the latter ing between the artery and the vein, on a plane posterior to both, t the lower part of the neck, on the right side, the internal jugular ein leaves the common carotid artery, making a slight interval in hich the right vagus nerve appears as it is about to pass in front F the first part of the right subclavian artery. On the left side,


12 IO


A MANUAL OF ANATOMY


however, the internal jugular vein is very closely related to the commo carotid artery, and even overlaps it.

Medial .—From below upwards (i) the trachea and oesophagu: with the recurrent laryngeal nerve and the inferior thyroid arter lying in the intervening groove; (2) the corresponding lobe of th thyroid gland, upon which the vessel impresses a groove, and by whic it is usually overlapped; and (3) the larynx and pharynx.


Accessory Part of Parotid Gland

Parotid Gland ! _ ., ,

Parotid Gland


Transverse Facial Artery i


Superficial Temporal Artery Maxillary Artery


Mental Branch of Inferior Dental | Artery


Facial Artery Lingual Artery


Inferior Thyroid Artery_


__ Posterior Auricula Artery


\Occipital Artery


Greater Occipital Nerve

Internal Carotid Artery


External Carotid Artery.I Superior Laryngeal Artery , Superior Thyroid Artery

Vagus Nerve ( Internal Jugular Vein l C ommon Carotid Artery V

Superior Belly of Omo-hyoid __ Ascending Cervical Artery _.J


Deep Cervical " Lymph Glands


Phrenic Nerve


! \

Subclavian Artery (first part) \


Scalenus Anterior Muscle

Transverse Cervict Artery


\ Suprascapular Artery Thyro-cervical Trunk


Fig. 729.—Deep Dissection of the Left Side of the Neck

(after Spalteholz).


The common carotid artery, as a rule, gives off no branch. Th superior thyroid artery, however, may arise from it superiorly, and i some cases the ascending pharyngeal artery.

Surgery—Compression. —The part of the vessel most favourabl situated for compression lies in front of the tubercle of the transvers process of the sixth cervical vertebra, this tubercle, known as th carotid tubercle, being on a level with the cricoid cartilage of the larynx Ligation. —The part of the vessel most favourably placed fo ligation is situated on a level with the cricoid cartilage just abov the point where it is crossed by the anterior belly of the omo-hyoi'












THE HEAD AND NECK


1211


,cle. The structures to be avoided in the operation are: (i) the us descendens hypoglossi upon, or it may be within, the sheath; the internal jugular vein and vagus nerve, both of which are lin the sheath, and upon the outer side of the artery; and (3) the ipathetic trunk, which lies behind and in close contact with the ith. The small sterno-mastoid branch of the superior thyroid

ry will probably be cut, as it passes obliquely downwards and

wards over the sheath in the carotid triangle. Ligation of the

ry below the level of the cricoid cartilage is attended with diffi
y, the vessel being here covered by the sterno-hyoid and sternoroid muscles, in addition to the platysma and sterno-mastoid.

the left side the internal jugular vein is an additional difficulty. Collateral Circulation after Ligation. —(1) Cross anastomoses take

e freely between the external and internal carotid arteries of

losite sides. (2) The inferior thyroid artery of the side operated ►n anastomoses freely with the superior thyroid of the same side, ch is a branch of the external carotid. (3) The deep cervical nch of the superior intercostal, which latter is a branch of the Dnd part of the subclavian artery on the right side, and of the t part on the left side, anastomoses with the descending branch the occipital, which is a branch of the external carotid. (4) The tebral artery undergoes much enlargement.

Carotid Body.— This small body is situated behind the common otid artery close to its bifurcation. It is composed of a few lobules ted by connective tissue, and it receives minute twigs from the acent part of the common carotid artery. The lobules consist groups of polyhedral cells permeated by blood-capillaries and apathetic nerve-filaments. Some of the cellular constituents are omaffin cells, similar to those which are met with in the medulla the suprarenal gland and in the sympathetic ganglia. These cells derived from the contiguous ganglia of the sympathetic system, e carotid body of each side is similar to the glomus coccygeum 1 organs of Zuckerkandl.

The carotid body is developed in part from the sympathetic system, and in

t from the lymphatic system. # _ , ,, , ,

Development.— The common carotid arteries are developed from the parts of ventral aortae which are situated between the third and fourth aortic arches.

Internal Jugular Vein. —The internal jugular vein is the continuon of the intracranial sigmoid sinus. It begins in the posteroeral compartment of the jugular foramen, and ends behind the ler end of the clavicle by joining the subclavian to form the j nn o~ nate vein. At its beginning it has a slight dilatation, called the berior bulb. The vein descends vertically, lying at first on the outer e of the internal carotid, and then on the outer side of the common ~otid artery, the vagus nerve being interposed in each case, and being enclosed within the carotid sheath. The relations of the ssel for the most part correspond to those of the artenes which 1

companies.


1212


A MANUAL OF ANATOMY


Tributaries.—These are as follows:


Pharyngeal. Superior thyroid. Middle thyroid.


Inferior petrosal sinus.

Common facial.

Lingual.

A small vein accompanying the occipital artery may occasional open into it.

Hypoglossal Nerve

Second Cervical Nerve / Occipital Artery


Accessory

Nerve


Lesser Occipital Nerve


Great Auricular Nerve


R am i Communicantes ( Cervicales \


Fourth Cervical Nerve


Descending Branch of Fourth Cervical Nerve


Supraclavicular Nerves


External Jugular

vd " (ci '° /if

Nerve to Subclavius jdjP®®


Subclavian Vein


Vagus Nerve

Nerve to Thyro-hyoid Muscl


Terminal Branches M Hypoglossal Ner


Internal Laryngea Nerve


External Larynge; Nerve

— Ramus Descenden Hypoglossi

-Nerve to Superior I

of Omo-hyoid Ansa Hypoglossi



Anterior J ugular V

- -. Internal Jugular V


v //i/lfJM


Fig. 730. —Deep Dissection of the Right Side of the Neck (after

Hirschfeld and Leveill£).

1, upper part of sterno-mastoid; 2, trapezius; 3, tendon of omo-hyoid.


The inferior petrosal sinus leaves the cranial cavity through th antero-medial compartment of the jugular foramen, and opens int the internal jugular vein close to the base of the skull.

Development. —The internal jugular vein is developed from the anteric cardinal vein.

The vagus nerve in the neck will be found described on p. 1327.

External Carotid Artery.—The external carotid artery is one c the terminal branches of the common carotid, the other being th internal carotid artery. In spite of its name, it is, at its origin, th medial of the two vessels, and it lies anterior to, and nearer the media









THE HEAD AND NECK


1213


than, the internal carotid. It extends from a point on a level 1 the upper border of the thyroid cartilage to one immediately ind the neck of the mandible, where it divides in the substance of parotid gland into the superficial temporal and maxillary arteries, s about 2J inches in length, and its direction is at first upwards forwards as far as the angle of the mandible, and then upwards backwards. At first the artery lies in the carotid triangle, and is iparatively superficial. As it leaves this triangle it is more deeply

ed, being crossed by the posterior belly of the digastric and styloid muscles, and the hypoglossal nerve. Then the vessel is eroded in the substance of the parotid gland, where it is crossed from

ind forwards by the facial nerve.

Relations.— Antero--lateral. —The skin; superficial fasciaplatysma; p fascia; anterior border of the sterno-mastoid; the lingual and imon facial veins; the hypoglossal nerve (all the foregoing being grior relations, whilst the artery lies in the carotid triangle); the terior belly of the digastric and stylo-hyoid muscles; the greater t of the parotid gland; the posterior facial vein; and the facial ve. Deep or Postero-medial. —(1) The stylo-pharyngeus muscle,

so-pharyngeal nerve, and styloid process of the temporal bone,

of which lie between the vessel and the internal carotid (the latter g lying on a plane behind the external carotid); and (2) a small tion of the parotid gland. The pharynx and hyoid bone; the erior laryngeal nerve; a portion of the parotid gland; and the terior border of the ramus of the mandible.

The external carotid artery has no vein in the sense of a companion sel, but the posterior facial vein descends superficially to it in the otid gland to near the angle of the mandible, beyond which point artery has no vein.

The course of the vessel may be indicated by a line drawn from side of the cricoid cartilage of the larynx to the tragus of the icle.

Development. —The external carotid artery is, for a short portion of its rse, the persistent part of the ventral aorta above the level of the third aortic 1. In the rest of its extent it is formed from enlarged side-branches of the inal stem.

Branches.—These are arranged in four sets ending, and terminal—and are as follows:

Anterior. Posterior. Ascending.

'erior thyroid. Occipital. Ascending

glial. Posterior auricular. pharyngeal.

ial.

Superior Thyroid Artery.—This vessel arises in the carotid tiiangle m the front part of the external carotid close to its oiigin. It

es an arched course forwards and downwards, passing undei covei

the infrahyoid muscles. On reaching the apex of the corresponding >e of the thyroid gland it breaks up into its terminal branches,


—anterior, posterior,

Terminal.

Superficial temporal. Maxillary.


1214


A MANUAL OF ANATOMY


which enter the lobe on its superficial aspect, and anastomose free within it with branches of the inferior thyroid artery, and in the isthm with its fellow of the opposite side.

Branches:

Infrahyoid. Crico-thyroid

Sterno-mastoid. Glandular.

Superior laryngeal. Muscular.

The infrahyoid artery passes inwards on the thyro-hyoid membrar deep to the thyro-hyoid muscle, and close to the lower border of i


Fig. 731. —Dissection of Carotid Triangle.

hyoid bone. It anastomoses at the middle line with its fellow of t opposite side, and with the suprahyoid branch of the lingual arte: of the same side. The sterno-mastoid branch passes obliquely downwar. and outwards, lying superficial to the carotid sheath, to enter the de< surface of the muscle from which it takes its name. It is liable to cut in tying the common carotid artery. The superior laryngeal arte accompanies the internal laryngeal nerve, and, passing deep to tj outer border of the thyro-hyoid muscle, pierces the thyro-hycl membrane, to be distributed to the interior of the larynx. The cril thyroid branch passes transversely inwards upon the crico-thyrC ligament, and anastomoses with its fellow of the opposite side to foil


Hypoglossal


Digastric Post. Belly

Comm. Facial V.


N. Desc. Hypog. Sup. Laryng. N. Inf. Constrict.


. Laryng. N. >uter div.)

Sup. Thyr. V.

Omo-hyoid

Sterno-hyoid





THE HEAD AND NECK


1


1215


crico-thyroid arch. The glandular branches are distributed to the responding lobe of the thyroid gland. They anastomose freely h branches of the inferior thyroid of the same side, and with branches the fellow of the opposite side to a less extent. One very constant .nch, known as the artery of the isthmus, courses along the upper -der of the isthmus, and anastomoses with its fellow of the opposite e. The muscular branches are distributed to the infrahyoid muscles. The superior thyroid vein issues from the upper part of the corremding lobe of the thyroid gland, and crosses in front of the common otid artery near its bifurcation to open into the internal jugular n. Its tributaries for the most part correspond to the branches the artery.

Lingual Artery. —The lingual artery arises from the front part of i external carotid a little above the origin of the superior thyroid d opposite the greater horn of the hyoid bone. From its comcated course it is convenient to divide the artery into three parts.


Dorsum of Tongue

Sublingual Gland (turned >

UP) !


Stylo-glossus Muscle N Lingual Nerve

x


Submandibular Ganglion

Submandibular Gland (deep part)

^Facial Artery


Mandible . (in section)


Genio-glossus Muscle , (

Genio-hyoid Muscle ! Sublingual Artery Arteria Profunda Linguae


_Lingual Artery

_Sup. Thy. Artery

. Ext. Car. Artery

\ \ Vena Comitans Hypoglossi

t Hypoglossal Nerve

Submandibular Duct


Fig. 732.—Deep Dissection of the Left Submandibular Region.


First Part. —The first part of the vessel ascends for a little, and en, bending sharply, descends to the greater horn of the hyoid bone, issing deep to the posterior belly of the digastric and stylo-hyoid uscles. So far the vessel lies in the carotid triangle, and the bend tiich it describes is crossed by the hypoglossal nerve. It is for the ost part comparatively superficial.

Second Part. —The second part passes horizontally forwards along ie upper border of the hyoid bone deep to the hyo-glossus, the hypoossal nerve and its vena comitans being superficial to that muscle, eep to it is the middle constrictor. At the anterior border of the ^o-glossus it enters upon the third part of its course.

Third Part.— Near the anterior border of the hyo-glossus muscle ie lingual artery describes another sharp bend in an upward direction, id ascends almost vertically to the under surface of the tongue,

sting upon the genio-glossus, and being under cover of the anterior

irder of the hyo-glossus. Having reached the tongue, the artery




1216


A MANUAL OF ANATOMY


passes forwards on its under surface in a tortuous manner under th name of arteria profunda linguae.

Branches:

1. Suprahyoid. 3. Sublingual.

2. Rami dorsales linguae. 4. Arteria profunda linguae.

The suprahyoid artery arises from the lingual at the posterior horde of the hyo-glossus, and passes along the upper border of the hyof bone.

The rami dorsalis linguce arise under cover of the hyo-glossn muscle, which they pierce, and so reach the posterior third of th


Superficial Temporal \

Occipital

Maxillary

Posterior Auricular


Transverse Facial


Supraorbital

Supratrochlear


Angular

Lateral Nasal

Superior Labial Inferior Labial


Submental Submandibular Gland


Internal Carotid '


External Carotid


Lingual

Suoerior Thyroid


Fig. 733. —The Arteries of the Right Side of the Head (after

L. Testut’s ‘ Anatomie Humaine ’)•

dorsum of the tongue. They are distributed to the mucous membran and substance of the tongue, the tonsil, and the soft palate.

The sublingual artery arises close to the anterior border of th hyo-glossus muscle. It supplies the sublingual gland, the adjacen muscles, and the mucous membrane of the floor of the mouth. On of the lateral branches anastomoses at the median line with a com sponding branch of the opposite artery, and another of them is know as the artery of the frenulum linguce.

The arteria profunda linguce [ranine artery) is the terminal pai of the lingual. It passes forwards on the under surface of the tongu< lying immediately lateral to the insertion of the genio-glossus, betwee







THE HEAD AND NECK


1217

id the longitudinalis linguae inferior. It is more or less embedded le substance of the tongue, and its course is tortuous in adaptation tie mobility of the organ to which it is so intimately related. ToIs the tip of the tongue the vessel is very superficially placed, close by the side of the frenulum linguae, and it anastomoses l its fellow of the opposite side near the tip. Elsewhere the cross domoses are remarkable for their absence, and if one lingual artery led with fine injection hardly any crosses the mid-line of the tongue pt at the tip. The arteria profunda linguae furnishes branches y to the substance of the tongue. Its close relation to the frenulum rae is to be carefully noted in connection with the operation for f of tongue-tied children.

rhe lingual veins are as follows: (1) the vena comitans hypoglossi ine vein), which is of large size, commences under the tip of the pe, and passes backwards, in company with the hypoglossal nerve,

rficial to the hyo-glossus muscle, receiving tributaries from the

ounding structures; (2) two vence comitantes accompanying the ral artery; and (3) the dorsal lingual veins, which originate in a us beneath the mucous membrane over the posterior third of the .n. These three sets of veins may join into a common trunk, called lingual vein, which opens into the internal jugular vein, or they r terminate independently in that vein.

jingual Lymph Glands.—These glands, which are of small size, pon the outer surfaces of the genio-glossus and hyo-glossus muscles, g the vena comitans hypoglossi. They are really small glandions lying in the course of the lymphatic vessels of the tongue hese pass to join the deep cervical lymph glands.

Facial Artery.—The facial artery arises from the front part of external carotid in the carotid triangle immediately above the nal artery, or sometimes in common with that vessel. It passes ards and forwards deep to the hypoglossal nerve, the posterior 7 of the digastric and the stylo-hyoid muscles, into the submanilar triangle. It then becomes embedded in a groove on the upper back part of the submandibular gland, its general course being ^ards with many curves. From this groove it describes a sharp i upwards over the base of the mandible in front of the masseter cle. The vessel then enters upon the facial part of its course, for scription of which see p. 1278.

Branches. —Four branches arise from the cervical part of the facial ry:

1. Ascending palatine. 3. Glandular.

2. Tonsillar. 4. Submental.

rhe ascending palatine artery passes upwards between the stylosus and stylo-pharyngeus muscles, and then over the upper ler of the superior constrictor of the pharynx along with the levator ti muscle. It is distributed to the soft palate, tonsil, and auditory The tonsillar artery passes upwards between the stylo-glossus

77


1218


A MANUAL OF ANATOMY


and medial pterygoid muscles, and, after piercing the superior c< strictor muscle, it is distributed to the tonsil and the posterior p of the side of the tongue. The glandular branches axe distributed the submandibular gland. The submental artery arises from i facial just below the mandible, and passes forwards superficial the mylo-hyoid muscle. It gives branches to the submandibular gla and mylo-hyoid muscle, some of the branches piercing that mus to reach the sublingual gland and anastomose with the subling artery.

The cervical part of the anterior facial vein passes downwai and backwards superficial to the submandibular gland. Hav: received tributaries corresponding to the branches of the cervical p of the artery, it unites with the anterior division of the posterior fac vein to form the common facial vein, which opens into the inter: jugular opposite the body of the hyoid bone.

Occipital Artery. —The occipital artery arises from the poster aspect of the external carotid opposite the facial artery. It pas

at first upwards and sligh


UATERfll

J>IC,


r rvi T. CAROT.


MX 1.


NJ.X 11


occ i P.

ARTERV.


Fig. 734.—Plan of Course of Occipital Artery in Neck.


backwards beneath the poster belly of the digastric and sty hyoid muscles, and the hy] glossal nerve, having hool round it, passes forwards sup ficial to it. Having reached level of the interval between 1 transverse process of the at and the mastoid process, ' artery changes its course, a passes backwards to occupy occipital groove on the in: aspect of the mastoid proc( where it is in touch with rectus capitis lateralis. In t backward course it crosses


internal carotid artery, internal jugular vein, and vagus, accessc and hypoglossal nerves. As it lies in the occipital groove the ve< is very deeply placed, being covered by the following structui (1) the origin of the posterior belly of the digastric; (2) the lon$ simus capitis; (3) the splenius capitis; and (4) the sterno-mastc After escaping from beneath the splenius capitis, the vessel takes upward course superficial to the semispinalis capitis to the occip: region, where it ramifies in a tortuous manner along with the branc of the greater occipital nerve.

Branches. — Muscular; meningeal; mastoid; descending; s Occipital.

The muscular branches are distributed to the adjacent muse one of them, the sterno-mastoid branch, crosses the hypoglossal ne: and enters the deep surface of the sterno-mastoid muscle in comps



THE HEAD AND NECK


1219


the accessory nerve. The meningeal branch accompanies the internal lar vein, and enters the cranial cavity through the jugular foramen apply the dura mater of the posterior fossa. The mastoid branch es through the mastoid foramen when present, and supplies the cent dura mater. The descending and the occipital [terminal) Lches have been already described (see p. 1146).

Tie description of the occipital veins will be found on p. 1147. tosterior Auricular Artery. —This vessel arises from the posterior ct of the external carotid a little above the origin of the occipital ry, and above the posterior belly of the digastric. It passes ards and slightly backwards under cover of the lower part of the tid gland, and behind the styloid process of the temporal bone, g crossed by the facial nerve. Having reached the groove between back of the auricle and the mastoid process, where it meets the erior auricular nerve, it divides into two branches, auricular and aital.

branches. —These are as follows: muscular; glandular; stylotoid; auricular; and occipital.

rhe muscular branches supply the adjacent muscles. The glandular ches are distributed to the lower part of the parotid gland. The -mastoid artery enters the facial canal through the stylo-mastoid men. It is distributed to the tympanic cavity and the mastoid

ells, and anastomoses with the tympanic branch of the first part

ae maxillary artery. With this latter branch it forms a ring at the lmference of the tympanic membrane on its inner aspect. Within facial canal the stylo-mastoid artery anastomoses with the super1 petrosal branch of the middle meningeal artery, which branch rs the canal through the hiatus for greater superficial petrosal r e. The auricular branch passes upwards deep to the auricularis erior muscle, and furnishes branches to the inner aspect of the

le, some of which reach the outer surface by piercing the cartilage

by turning round its margin. The auricular branch anastomoses l the posterior branch of the superficial temporal artery. The 'ntal branch passes backwards over the mastoid process to the pital region, and anastomoses with the occipital artery, rhe posterior auricular vein, of fairly large size, often unites with posterior division of the posterior facial vein near the angle of inferior maxilla, and by this union the external jugular vein is led. The arrangement, however, is very variable.

Ascending Pharyngeal Artery. —This long, slender vessel arises from beginning of the deep surface of the external carotid. It runs ically upwards towards the base of the skull, lying very deeply 1 the longus capitis muscle, and between the internal carotid ry, in front of which it has passed, and the pharynx, branches :

1. Pharyngeal. 3. Prevertebral.

2. Palatine. 4. Inferior tympanic.

5. Meningeal.


1220


A MANUAL OF ANATOMY


The pharyngeal branches are distributed to the pharynx. TJ palatine branch passes over the superior constrictor muscle of t] pharynx, and is distributed to the soft palate, auditory tube, and tons The prevertebral branches supply the prevertebral muscles. T] inferior tympanic artery passes with the tympanic branch of the gloss pharyngeal nerve through the tympanic canaliculus in the petro part of the temporal bone, and so reaches the tympanic cavity, to t] inner wall of which it is distributed. The meningeal branches are t' terminal branches of the ascending pharyngeal, and are three in numbe One passes through the foramen lacerum, a second through the jugul foramen, and a third through the anterior condylar canal, to be d: tributed to the dura mater in the vicinity of these foramina.

The descending pharyngeal vein accompanies the ascending phary

geal artery.

For the superficial temporal and maxillary branches of the extern carotid artery, see pp. 1158 and 1304.

The internal carotid artery will be found described on p. 1323.

Thyroid Gland. —The thyroid gland is situated on either side the upper part of the trachea and larynx, and a small portion of it li in front of the upper part of the trachea. Its size is subject to mu variation; its weight is rather more than 1 ounce; and it is larger the female than in the male. It consists of right and left lobes and; isthmus.

Each lobe is conical and about 2 inches long, the rounded ba being directed downwards. It extends from the middle of the lami: of the thyroid cartilage to about the level of the fifth ring of the trache Its superficial surface , which looks forwards and outwards, is somewb convex, and is covered by the sterno-thyroid, sterno-hyoid, and superi belly of the omo-hyoid muscles. It is also overlapped by the anted border of the sterno-mastoid. Its deep surface is concave in adaptati to the trachea and larynx. The anterior border is thin, and towar its lower part is connected with that of the opposite lateral lobe means of the isthmus. The posterior border is thick, and is in conta with the pharynx and oesophagus, and has the parathyroid glan embedded in it. Each lobe overlaps the corresponding common carol artery, enclosed in the carotid sheath, and is frequently grooved by tb vessel. Interiorly it overlaps the recurrent laryngeal nerve and infer] thyroid artery. The apex of each lobe rests upon the inferior constrict muscle of the pharynx, and the superior thyroid artery enters it sup< ficially and deeply4

The isthmus is inconstant as regards size and position. Its dep ranges from J to 1 inch, and its breadth is about \ inch. It conne^ the lower parts of the anterior borders of the lateral lobes, but dc not reach quite so low as their bases. .It lies in front of the trach< usually upon the second and third rings, and fits closely to the rir upon which it rests. Along its upper border there is a branch of t superior thyroid artery, known as the artery of the isthmus, which an. tomoses with its fellow of the opposite side. From its lower bore


THE HEAD AND NECK


1221


?ral veins issue, which take part in the inferior thyroid plexus of is in front of the trachea.

In some cases an additional lobe is present, called the pyramidal !. It forms a long pyramid, which is attached by its base to the ier border of the isthmus, usually at its junction with the left lobe, apex is attached to the body of the hyoid bone by a fibrous band, ch sometimes contains muscular fibres, known as the levator glandulcz oidce muscle. It is seldom quite median in position.


erior Belly of Digastricand Stylo-hyoid lyo-glossus Muscle and’ Hypoglossal Nerve


Head of Sterno-mastoid Crico-thyroid Muscle Cricoid Cartilage t Lobe of Thyroid Body


Trapezius vicular Head of

7 / 7 ,


sterno-mastoid Brachial Plexus


Subclavian Artery (third part)

Clavicle


Anterior Belly of Digastric L Mylo-hyoid


Body of Hyoid Bone

Superior Belly of Omo-hyoid Sterno-hyoid

K ljnimr- Thyro-hyoid

USSr - Laryngeal Prominence "m sterno-thyroid


Superior Belly of Omo-hyoid Crico-thyroid Membrane

Sterno-hyoid


Isthmus of Thyroid Gland


Inferior Thyroid Plexus of Veins — - Cla. Head'd St.-mas. Sterno-thyroid

Sternal Head of Sternomastoid


Fig. 735

he area bounded below by the


Sterno-thyroid


Sterno-hyoid

—Dissection of the Front of the Neck.

on either side by the anterior belly of the digastric and body of the hyoid bone is the submental triangle.


The thyroid gland is invested by a fibrous sheath which is derived u the pretracheal layer of the deep cervical fascia.

When a portion or portions of the pyramidal lobe, or of the right or lobes, become detached, the isolated masses are known as accessory roids.

Blood-supply—Arteries. —The thyroid gland is very vascular. The • sries on either side are (i) the superior thyroid, which is a branch of external carotid; and (2) the inferior thyroid, which is a branch of thyro-cervical trunk of the first part of the subclavian. Occasion7 there is a third thyroid artery, called the arteria thyroidea ima, ich is derived from the innominate artery, or from the arch of the




















1222


A MANUAL OF ANATOMY


aorta, and is distributed to the isthmus, its position being in fro of the trachea at the median line, or close to it.

The veins are superior, middle, and inferior. The superior ai middle thyroid veins open into the internal jugular. The inferi thyroid veins, right and left, issue from a plexus of veins in front the trachea below the isthmus. The left vein opens into the 1 < innominate vein, whilst the right may open into the left innomina vein, into the angle of junction of the right and left innominate veil or into the lower part of the right innominate vein.

Nerves. —These are derived from the sympathetic plexuses whi accompany the superior and inferior thyroid arteries.

Lymphatics. —The lymphatic vessels the thyroid body are disposed in t groups —ascending and descending. T ascending lymphatics form three sets median and two lateral, right and le The median ascending lymphatics retn lymph from the upper part of the isthmi and pass to the prelaryngeal lym glands. The lateral ascending lymphat on either side accompany the super thyroid artery, and pass to the infer deep cervical lymph glands on a level wi the cricoid cartilage of the larynx. T descending lymphatics also form three st The median descending lymphatics retr lymph from the lower part of the isthm and pass to the pretracheal lymph glam The lateral descending lymphatics on eitl side accompany the inferior thyroid artery, and pass to the pa: tracheal lymph glands, which lie in the groove between the tract and oesophagus, the efferents of which terminate in the inferior de cervical lymph glands.

Structure. —The thyroid gland has an external capsule of dense connect tissue which sends trabeculae into the interior, thereby dividing it into irregu lobules. These lobules are composed of groups of closed vesicles, which ; connected together by areolar tissue. The vesicles are oval or spherical, a each is lined with a single layer of columnar or cubical epithelium. They cont; a yellowish viscid, albuminous fluid called colloid and are surrounded by n works of capillary bloodvessels.

Development. —The thyroid body is developed from the entoderm of 1 ventral wall of the pharyngeal portion of the primitive gut.

The first indication of the median thyroid is an evagination of the vent pharyngeal entoderm immediately behind the tuberculnm impar. This evagu tion is called the median thyroid diverticulum. It forms a thick-walled epithe. vesicle embedded in mesoderm, which soon becomes solid. As the vesicle grc its distal end becomes bilobed. Superiorly it retains for a little time its co munication with the ventral wall of the pharynx behind the tuberculum im] by a hollow pedicle, which constitutes the thyro-glossal duct (canal of H This duct usually disappears, its superior orifice being represented on the dorsi of the adult, tongue by the blind recess, called the foramen ccecum. In very r;


Fig. 736. — Section of the Thyroid Gland, showing the Vesicles and their Epithelial Lining.

The colloid is indicated.




THE HEAD AND NECK


1223


the lingual portion of the duct may persist for a short distance, in which the foramen caecum leads to the lumen of a short tube, known as the ductus %lis.

tie median thyroid, as stated, gives rise to the isthmus and lobes of the thyroid gland.

tie median bud almost from its beginning is in contact with the pericardial and the two ventral aortae arising from the truncus arteriosus; it extends these vessels. It lies in loose mesoderm ventral to the condensations e second and third visceral arches. As the head grows forward and the irdium assumes in consequence a more caudal position, the thyroid bud h has separated from its lingual attachment) remains in contact with the irdium and the vessels; thus it moves caudally with reference to the pharynloor above it, and as a result of its lateral extension at the same time along vessels, comes into relation with the ventral angle of the fourth lateral 1 (P- 77 )■ Becoming attached to this, its farther caudal dislocation is

>ed, save perhaps in the middle line, where some of its cells may still follow Dericardium in its retrogression. The main part of the bud, however, ins in its fixed position, and forms the lobes and isthmus, he ventral bud from the fourth pouch is sometimes termed the lateral id bud, being supposed to contribute to the formation of each lobe. It is •ally believed, however, that it does not do so, but remains as a small elial mass in the lobe; under some circumstances it appears to show a

ncy to thyroid vacuolization.

□nnective tissue derived from this mesodermic investment now invades the mass, and it is broken up into numerous solid epithelial cords, which

omose freely, and so give rise to an intricate reticulum, the meshes of which

ccupied by connective tissue and bloodvessels of mesodermic origin. The epithelial cords of the reticulum become hollow, and the lumina so produced )roken up at intervals by constrictions into closed vesicles , which contain olloid material.

he pyramidal lobe of the thyroid gland sometimes met with in connection the isthmus of the adult thyroid is developed from the median bud. he epithelial cells of the vesicles of the adult thyroid are derived from the lerm of the pharyngeal part of the fore-gut.

Parathyroid Glands. —The parathyroids are four in number, and are tiged in pairs. The upper pair are related to the dorsal borders ie lobes of the thyroid gland, and the lower pair are placed behind ower ends of the lobes. They are difficult to distinguish with the id eye, but the best way to find them is to follow the anastomosis reen the superior and inferior thyroid arteries. They are developed ^aginations of the entoderm of the third and fourth visceral pouches ther side. The parathyroids present no traces of closed vesicles he colloid material.

ccessory Thyroid Glands. —These glands are sometimes met in the neighhood of the hyoid bone, and are known as the suprahyoid and prehyoid !S. They are developed as buds or evaginations of the thyroglossal duct, they consist of thyroid tissue.


The Trachea and (Esophagus.

trachea. —The trachea extends from the cricoid cartilage of the nx to about the level of the disc between the bodies of the fourth fifth thoracic vertebrae, where it divides into the two bronchi, t and left. Its average length is about inches, and its width


1224


A MANUAL OF ANATOMY


about i inch. Anteriorly and laterally it is cylindrical and fi but posteriorly it is flattened and membranous, so that it does press upon the oesophagus, in front of which it lies. It occupie medial position, and its direction is downwards with an inclinat backwards. It is divisible into two parts, cervical and thoracic.

For the trachea in the thorax, see p. 1085.

The cervical part of the trachea extends from the cricoid cartil to the level of the upper border of the manubrium sterni, and it measr about 2 \ inches in length. It is freely movable, and is surroun<

by areolar tissue, which c


Epiglottis


Greater Horn of Hyoid Bone Lesser Horn of Hyoid Bone_

Body of Hyoid Bone —


Thyro-hyoid Membrane —

Levator Glandulae \ Thyroidm Muscle/

Thyroid Cartilage - Crico-thyroid Ligament Pyramidal Lobe f Cricoid Cartilage Right Lobe of Thyroid Gland _

Isthmus

Right Bronchus Eparterial Bronchus


Hyparterial Bronchus.._ f


Trachea


tains many elastic fibres, ; is somewhat loosely arrange Relations — A nterior. —' isthmus of the thyroid gli lies directly upon the sect and third rings as a rule, first ring usually lying expo between its upper border 1 the cricoid cartilage. Su] ficial to the first ring, on left of the median line, th may be the lower part of pyramidal lobe of the thyi gland. Below the isthmus the inferior thyroid plexus veins, from which the ri and left inferior thyroid v( pass downwards one on eit side of the median line. ' arteria thyroidea ima may cend to the isthmus of thyroid gland, lying in fr of the trachea at the med line, or slightly to the right it. The anterior jugular ve:


Fig.


Left Bronchus

737 .-The Hyoid Bone, Larynx, r ig ht and J eft - are a " teri “ Trachea, Bronchi, and Thyroid Gland it, and just above the ma (Anterior View). brium sterni it is crossed by

communicating branch wh passes between these two veins. In children under two years age the cervical portion of the thymus forms an important ante] relation. Close to the upper border of the manubrium sterni innominate artery may encroach slightly upon it. The pretract layer of the deep cervical fascia forms an anterior relation, as \ as the superficial layer of that fascia, which is here usually descril as dividing to form the suprasternal space above the supraster notch. Another, and perhaps more common-sense, description is say that in front of the trachea is a layer of cellular tissue c











THE HEAD AND NECK


1225


Lateral Thyrohyoid Ligament

Upper Border of Thyroid Cartilage


Epiglottis


— Cartilago Triticea

_Corniculate Cartilage

-Arytenoid Cartilage

f_i.__Cricoid Cartilage

ft 3

Vfj--Right Lobe of Thyroid Body


)us with that in which the thyroid gland is embedded, and that tissue increases in thickness from before backward as the lea recedes from the surface on approaching the thorax. Other rior relations are the anterior jugular veins, along with one or two )h glands, and in some cases the left innominate vein. The sternod and sterno-thyroid muscles cover it in the following manner: derno-hyoid muscles are separated by an interval below, but they 3 nearly into contact above; and the sterno-thyroid muscles are intact below, but diverge above. Between the muscles of opposite 1 there is a very narinterval, along which trachea is free from cular covering. lateral .—The trachea fiosely embraced on sr side by the lobes he thyroid gland as as about the level of fifth ring, and lateral this is the carotid .th with its contents, common carotid artery g nearest the lobe.

Posterior .—The trachea n front of the cesogus, which projects a e to its left side tods the root of the neck, ween the two there is groove, in which the irrent laryngeal nerve inferior laryngeal

ry ascend. For a reflce to the high and

operations of tracheny, see p. 1174.

Blood-supply. —The ar- , ,,

es of the cervical part of the trachea are derived from the m or thyroid of each side, which is a branch of the thyro-cervica nk

The veins terminate in the inferior thyroid plexus and inferioi

roid veins. . , , ,

The lymphatics pass to the inferior deep cervical lymph glands

Pretracheal Lymph Glands. —These glands lie upon the front of e deal part of the trachea, below the isthmus of the thyroid gland, fir afferent vessels are derived from the front of the trachea, an lower part of the isthmus of the thyroid gland. Their efferent sels pass to the inferior deep cervical lymph glands. The lymphatic


Fig. 7^8.—The Epiglottis, Larynx, Trachea, Bronchi, and Thyroid Gland (Posterior View).





1226


A MANUAL OF ANATOMY


vessels of the cervical part of the trachea pass to the pretrache; inferior thyroid, and inferior deep cervical lymph glands.

Nerve-supply.— The nerves are derived from the vagus, recurre: laryngeal, and sympathetic.


Structure. —The trachea is composed of about twenty so-called rings hyaline cartilage, which are incomplete posteriorly. They serve to keep t tube permanently open for the transmission of air, and are embedded in fibro tissue, which also connects together their contiguous borders. They are hon shoe shaped, and each forms rather more than two-thirds of a circle, being fl externally and convex internally. The deficient portions of the rings are plac posteriorly, and here each ring ends in two round extremities. The inters between these extremities are bridged over by fibrous tissue continuous wi that which connects the borders of the rings and in which they are embedde

In some cases a ring m;


Ciliated Epithelium Basement Membrane


Mucosa


_ Elastic Fibres


Submucosa, with Mucous Glands


Hyaline Cartilage of Ring


Fibrous Investment


Fig. 739. —Longitudinal Section of the

Trachea.


end in a bifurcated e tremity, or it may jc one of the adjacent rin^ The lowest ring is dee and its lower border pr jects backwards so as form a ridge betwe the openings of the t\ bronchi.

In the posterior w< of the trachea within t fibrous layer there is continuous layer of u: striped muscular tissu the fibres of which e tend transversely betwe* the ends of the rings which they are attache In the intervals betwe< the extremities of ti rings they are attach* to the fibrous coat. The fibres serve to approj mate the ends of t] rings, and so diminish t] calibre of the tube.


The submucous coat consists of loosely-arranged areolar tissue, and contai] the larger bloodvessels and nerves, together with the mucous glands.

The mucous coat consists of areolar and elastic tissues, and a large amoui of lymphoid or adenoid tissue. It contains the ramifications of the arteri and nerves, as well as the lymphatics. Superficial to the mucosa there is well-marked basement membrane which supports the epithelium. The dee portion of the mucosa consists principally of elastic fibres. On the poster! wall these elastic fibres are very numerous, and are arranged in longitudin bundles which give rise to elevations of the mucosa.

The epithelium is of the stratified columnar ciliated variety.

The wall of the trachea contains many mucous glands. Some of these a situated in the submucous coat. Others, which are of large size, lie on t posterior wall, where they are very superficial, many of them appearing li small grains superficial to the fibrous layer. Others are contained within t. fibrous layer. The ducts of these glands have to pass through the muscula elastic, and mucous walls of the tube.

Development. —The trachea is developed from the lower part of the laryng























THE HEAD AND NECK


1227


ial tube from the ventral aspect of the fore-gut superiorly, the upper part is diverticulum giving rise to the larynx.

Esophagus.—The oesophagus is that part of the alimentary canal h extends from the pharynx to the stomach. In the neck it ns on a level with the lower border of the cricoid cartilage, and on a level with the upper border of the manubrium sterni. It >mpressed from before backwards and between the trachea and the vertebral mn covered by the longus cervicis cles. At first it occupies the median but as it descends it inclines slightly ie left side, so as to be partly visible on left side of the trachea, delations— Anterior. —The trachea; the

erior parts of the lobes of the thyroid

y ; the recurrent laryngeal nerves; and inferior thyroid arteries. Posterior. —The ebral column and the longus cervicis icles covered by the prevertebral cellular ie. Lateral. —On either side there is the )tid sheath with its contents. The right left recurrent laryngeal nerves are inately related to the oesophagus, and md on each side in the groove between nd the trachea.

The cervical part of the oesophagus reres its blood-supply from the inferior roid arteries, which accompany the corDonding recurrent laryngeal nerves.

Paratracheal Lymph Glands (Inferior rroid Lymph Glands).—These glands lie the groove between the cervical parts of trachea and oesophagus, along the course the inferior thyroid artery and recurrent ^ngeal nerve. Their afferent vessels are ived from (1) the lower part of the lobe p IG —schematic View

the thyroid body, and (2) the adja- of CEsophagus.

it parts of the trachea and oesophagus.

eir efferent vessels pass to the inferior deep cervical lymph glands. For a description of the oesophagus in the thoiax, including its

ucture and development, see p. 1087. .

Suprahyoid Region—Muscles—Digastric. The digastric muscle isists of two bellies, posterior and anterior. Origin. The posterior ly arises from the mastoid notch on the inner aspect of the mastoid ft of the temporal bone; and the anterior belly arises from the distric fossa on the inner surface of the base of the mandible close to

"symphysis.

Insertion. —The two bellies end upon an intermediate tendon,










1228


A MANUAL OF ANATOMY


about 2 inches long, which is inserted by means of a broad fibr band into the anterior surface of the body of the hyoid bone at outer part, and the adjacent portion of the greater horn.

Nerve-supply .—The posterior belly is supplied by the facial nei and the anterior belly by the mylo-hyoid branch of the inferior den a branch of the mandibular nerve.

The posterior belly is directed downwards and forwards, and anterior belly downwards and slightly outwards.

Action .—To elevate the hyoid bone, as in the act of deglutiti and to depress the mandible.

Relations. —The posterior belly is at first deeply placed, be overhung by the mastoid process, and lying under cover of the Ion simus capitis, splenius capitis, and sterno-mastoid muscles. It is ; overlapped by the lower part of the parotid gland. It crosses external and internal carotid arteries, internal jugular vein, ;

hypoglossal nerve, stylo-hyoid muscle above it, and the hy glossal nerve below it a short distance. i intermediate tendon embraced by the fibres the stylo-hyoid mus This tendon crosses hypoglossal nerve, ; forms two sides of a angle, known as the angle of Lesser, the b of which is directed wards, and is formed the hypoglossal nerve. In the area of this triangle is a portion the hyo-glossus muscle, and deep to this is the lingual artery. 1 anterior belly, which is shorter than the posterior, is covered the integument, platysma, and deep cervical fascia. It rests u{ the mylo-hyoid muscle, and forms part of the floor of the digasl triangle. Its inner border is connected with that of its fellow b] fascial expansion.

The posterior belly of the digastric, along with the stylo-hyoid muscle, the stapedius muscle, is associated with the posterior end of the second vise or hyoid arch. The nerve of this arch is the facial nerve, and this explains nerve-supply of the posterior belly.

The anterior belly is associated with the anterior or medial end of the ) visceral or mandibular arch. The nerve of this arch is the mandibular from trigeminal nerve, thus accounting for the nerve-supply of the anterior belly Stylo-hyoid — Origin .—The posterior and outer aspect of the sty! process of the temporal bone near its base.

Insertion .—The anterior surface of the hyoid bone at the junct of the body and greater horn.


5TVIOHVOIP


Fig. 741. —Plan of Main Deep Relations of Digastric in Anterior Triangle.





THE HEAD AND NECK


1229


erv e-supply. —The facial nerve.

he muscle is directed downwards and forwards.

ction. _To draw the hyoid bone upwards and backwards.

he muscle lies close above the posterior belly of the digastric, before taking insertion, it usually splits into two bundles, which ■ace the intermediate tendon of the digastric. It is morphological delamination of the same sheet as the posterior belly of the di•ic, which explains its nerve-supply.

[ylo-hyoid — Origin. — The mylo-hyoid line of the mandible. nsertion— The posterior fibres are inserted into the anterior surface .e body of the hyoid bone; and the principal part of the muscle is ted into a central fibrous raphe, which extends from the symphysis ti on its deep and lower aspect to the body of the hyoid bone.


Mandible


Raph


)-hyoid Muscle - Lingual Nerve

Deep Part of nandibular Gland Post. Belly of Digastric Hypoglossal Nerve Stylo-hyoid


Body of Hyoid Bone


e


Infrahyoid Muscles


Fig. 74 2.—The Mylo-hyoid Region. Anterior belly of digastric removed.


Nerve-supply. —The mylo-hyoid branch of the inferior dental nerve, ch is a branch of the mandibular nerve.

The muscle is directed downwards and f01 wards.

Action.— To raise the floor of the mouth, and, in doing so, to ss the tongue against the hard palate, as in the first stage of the of deglutition; to elevate the hyoid bone, and diaw it forwards,

L to depress the mandible. .

The two mylo-hyoid muscles form a muscular floor for the buccal

ity, which is known as the diaphragma oris. >

Relations —Superficial or Inferior .—The anterior belly of the ditric; the superficial part of the submandibular gland, lodging a 'tion of the facial artery; and the mylo-hyoid nerve and submenta mch of the facial artery.



1230


A MANUAL OF ANATOMY


Posterior Border .—Passing deep to the posterior free border of muscle there are the following structures, in order from above do wards: (i) the lingual nerve; (2) a portion of the submandibular gla and (3) the hypoglossal nerve and its vena comitans.

Deep or Superior. —The hyo-glossus muscle, external to which the lingual nerve, the submandibular ganglion, the deep part of the s mandibular gland and the submandibular duct, the hypoglossal ne and its vena comitans. In front of the hyo-glossus is the genio-h} muscle, and between it and the hyo-glossus is a portion of the gei glossus, with the sublingual gland resting upon it.

Genio-hyoid— Origin. —The inferior genial tubercle of the mand close to the symphysis on its deep aspect.

insertion .—The inner two-thirds of the anterior surface of body of the hyoid bone over its upper part. At its insertion the mu is divided externally into two laminae, anterior and posterior, former of which extends farthest out upon the hyoid bone. The ini most fibres of origin of the hyo-glossus pass inwards between tl two laminae.

N erv e-supply. —The hypoglossal nerve, the branch of which is garded as being composed of spinal fibres.

The muscle is directed downwards and slightly backwards.

Action. —To elevate the hyoid bone and draw it forwards, and depress the mandible.

The muscle is in intimate contact with its fellow of the oppo side at the median line. Its inferior or superficial surface is cove by the mylo-hyoid, and its superior or deep surface is related to lower or posterior border of the genio-glossus.

Genio-glossus— Origin. —The upper genial tubercle of the mand close to the symphysis on its deep aspect.

Insertion. —The under surface of the tongue close to the med line, and extending from near the tip to the root; very slightly i the inner part of the anterior surface of the body of the hyoid b close to its upper margin; and slightly into the side of the phary where the fibres blend with those of the middle constrictor muscle.

N erv e-supply. —The hypoglossal nerve, the branches of which er the outer surface of the muscle.

The upper or anterior fibres arch upwards and forwards, and lower downwards and backwards, whilst the intervening fibres spr out in a fan-like manner.

Action. —The entire glossal fibres depress the tongue at the med line, and, along with those of the opposite side, they give rise to antero-posterior groove on the dorsum of the organ; the postei glossal fibres draw forwards the tongue, causing its tip to be protru< from the mouth; the anterior glossal fibres retract the tip of the ton] when it has been protruded from the mouth; and the lower or postei (hyal) fibres elevate the hyoid bone, and draw it forwards.

The muscle is fan-shaped. The medial surface is closely app] to that of its fellow of the opposite side. The lateral surface is rela


THE HEAD AND NECK


1231


ie longitudinalis inferior muscle, the arteria profundae linguae, the glossus and stylo-glossus muscles, and the sublingual gland. The rior border is covered by the buccal mucous membrane, and the r or posterior border by the genio-hyoid muscle, lyo-glossus— Origin. —The greater horn of the hyoid bone over its •e length; the anterior surface of the body of the bone over about uter half; and the lesser horn (inconstant). The innermost fibres rigin from the hyoid bone lie between the two laminae of the geniod muscle.


Tip of Styloid Process of Temporal Done


Fig. 743. —The Extrinsic Muscles of the Tongue. The longitudinalis inferior is an intrinsic muscle.


Insertion —The posterior half of the under surface of the tongue se to its lateral border, the fibres being situated medial to those of ! stylo-glossus, and both sets of fibres being intimately intermixed

h each other and with the intrinsic lingual muscles.

Nerve-supply .—The hypoglossal nerve, the branches of which enter

i superficial surface. , .. , .

The muscle is for the most part directed upwards, but its anterior

res have a slight inclination forwards.

Action .—To depress the side of the tongue, and, along with its low, to render the dorsum of the organ convex; and to assist m

xacting the protruded tongue.

The hyo-glossus is a flat, four-sided muscle.


1232


A MANUAL OF ANATOMY


Relations — Superficial. —The mylo-hyoid muscle; the intermedi tendon of the digastric, and stylo-hyoid muscle; the lingual nerve, w the submandibular ganglion lying a little below it; the deep part of submandibular gland, and the submandibular duct; the hypoglos nerve; and the vena comitans hypoglossi. Posterior Border .—The : lowing structures pass deep to this border in order from above do\ wards: the glosso-pharyngeal nerve; the stylo-hyoid ligament; and lingual artery. Deep .—The posterior part of the genio-glossus; a port of the middle constrictor muscle of the pharynx; the lingual arte the lower end of the stylo-hyoid ligament; and the glosso-pharyng nerve.

The fibres of the hyo-glossus which arise from the lesser horn the hyoid bone are separated from the rest of the muscle by th< fibres of the genio-glossus which take insertion into the side of i


Hyo-glossus Glosso-pharyngeal N.

Lingual N.-\ _

Hyo-glossus-_

Submandibular Duct-A - __

Vena Comitans Hypoglossi—\_ Al

Hypoglossal N.---X — ^


- -Longitudinalislnfi Stylo-glossus


Sublingual Gland Ant. Facial V. and Fat - Deep Submandibular G 1 • Sup. Submandibular Giant ' Mylo-hyoid

-/- Stylo-hyoid

~ —/Digastric

Hyoid Bone

\ ' Stylo-hyoid Lig.


Lingual ArteryA 'Middle Constrictor

Fig. 744.—Coronal Section through Submandibular Region.


pharynx, and they are vestigial remains of the chondro-glossus monkeys. These fibres, however, are inconstant.

Stylo-glossus — Origin .—The front of the styloid process of t temporal bone near its tip; and the upper extremity of the sty. mandibular ligament.

Insertion .—The under surface of the tongue close to its latei border. The fibres extend as far forwards as the tip, and are situat lateral to the fibres of the hyo-glossus, both sets of fibres being in mately intermixed with each other, and with longitudinalis inferi muscle.

Nerve-supply .—The hypoglossal nerve.

The muscle is directed downwards, forwards, and inwards.

Action. —(1) To draw the tongue backwards; and (2) to elevate t root of the tongue.

Stylo-hyoid Ligament. —This is a narrow fibrous cord which attached superiorly to the tip of the styloid process, and interiorly





THE HEAD AND NECK


1233


lesser horn of the hyoid bone. Its direction is downwards and ards, superficial to the glosso-pharyngeal nerve and deep to the rnal carotid artery, and its lower extremity is covered by the glossus muscle. It is liable to become ossified more or less pletely.

rhe ligament represents the usually unossified skeletal part of the nd visceral arch, and ossification in it, when it occurs, corresponds le epihyal bone of lower mammals, so well seen in the ruminants, lubmandibular Gland (Submaxillary Gland).—This gland is situated he anterior part of the digastric triangle. It consists of a large jrficial part and a small deep part. The superficial part superiorly ipies the submandibular fossa on the inner surface of the body of mandible, and inferiorly it is covered by skin, superficial fascia, platysma, and ) fascia. The anterior facial vein deds superficial to it. Its deep surface 3 anteriorly upon the mylo-hyoid muscle,

1 the intervention of the mylo-hyoid ^e and submental branch of the facial ry; and posteriorly upon the hyo-glossus, slightly upon the posterior belly of the istric and stylo-hyoid muscles. The jrficial part is grooved at its upper and £ part by the facial artery, which lies >edded in the gland. Posteriorly the jrficial part is related to the cervical ion of the parotid gland, from which s separated by the stylo-mandibular ment. The deep part of the gland is of .11 size, and is continuous with the superficial part at the posterior ier of the mylo-hyoid muscle. It lies under cover of that muscle n the hyo-glossus, and is related to the sublingual gland.

Ihe submandibular duct (Wharton’s duct) emerges from the deep set of the superficial part of the gland close to the posterior border he mylo-hyoid muscle. It is about 2 inches in length, and passes ards upon the hyo-glossus muscle, lying beneath the deep part of gland. In this situation it has the submandibular ganglion and ual nerve above it, and the hypoglossal nerve below it. After dng the hyo-glossus muscle, the duct lies superficial to the geniossus, and, passing slightly upwards, it is crossed from above down'ds by the lingual nerve. Having passed just below the mucous nbrane of the floor of the mouth on the inner side of the sublingual id, the duct opens upon the floor of the mouth by a minute orifice, ch is situated on the summit of a papilla lying close to the side of frenulum linguae.

The submandibular gland corresponds to the posterior half of the ly of the mandible, and sometimes reaches down below the level of hyoid bone.


Lumen of Alveolus


Crescents of Gianuzzi


Fig. 745.—Section of the Submandibular Gland of a Dog.


78




A MANUAL OF ANATOMY


1234

Blood-supply.—The gland derives its blood chiefly from the cerv part of the facial artery.

Nerve-supply.—The nerves are derived from the submandibi ganglion, and through this from the chorda tympani, the lingual, < the sympathetic plexus on the facial artery.

Lymphatics.—These pass to the submandibular lymph glands, < thence to the superficial and deep cervical lymph glands.

Structure. —The submandibular gland is a muco-serous gland, and its gen structure is similar to that of the parotid gland. The essential difference tween the two has reference to the alveoli or acini, and the nature of t secretion. The cells of the parotid alveoli are serous or albuminous. The 1 mandibular alveoli contain around the lumen mucous cells filled with gran mucigen, which is discharged as mucus. They, however, also contain s< albuminous cells, known as the marginal cells, which are situated externa


Parotid Duct


the mucous cells, but within the membrana propria of the alveolus. Th cells usually form groups which, from their crescentic arrangement, are knc as the crescents of Gianuzzi.

Development. —The submandibular gland is developed as a solid outgro of the buccal epithelium. This outgrowth undergoes ramifications, and fl subsequently become hollow. The outgrowth takes place from the floor of sulcus between the tongue and the mandibular arch, far back in its lateral p at the beginning of the second month. The lingual nerve passes to the ton below the floor of the sulcus in front of the outgrowth. The submandibular d is gradually produced from before backwards by the closing off of the lov part of the sulcus, so that it really corresponds with the original floor of groove. Thus it possesses a lumen from its earliest stages, while the glan< still solid, and the lingual nerve has to pass below it.

Sublingual Gland.—This is the smallest of the salivary glands, '< resembles an almond in shape. It measures about i\ inches in len£ and is situated beneath the mucous membrane of the floor of mouth, where it gives rise to a mucous fold, called the plica sublingua





THE HEAD AND NECK


1235


iriorly it rests upon the mylo-hyoid muscle, and is here related to deep part of the submandibular gland, the submandibular duct, L the lingual nerve. Laterally it occupies the sublingual fossa on inner surface of the body of the mandible above the mylo-hyoid and medially it is in contact with the genio-glossus muscle. Its dial extremity comes into contact with its fellow of the opposite 3 over the anterior border of the genio-glossus muscle.

The sublingual ducts (ducts of Rivini) vary in number from ten to

nty. A few of them open into the submandibular duct, but the

jority open in a linear manner upon the summit of the plica sub;ualis.

Blood-supply.—The gland receives its blood from the sublingual rich of the lingual artery.

Nerve-supply.—The nerves are derived from the chorda tympani 1 lingual nerves, and the sympathetic plexus on the facial artery, means of a branch of the submandibular ganglion, which is con:ted to the sublingual gland by the lingual nerve.

Structure. —-The sublingual gland is a mucous gland, and its general structure imilar to that of the parotid and submandibular glands, but the lobules are re loosely arranged. The cells of the sublingual alveoli are for the most part cous cells, but there are also serous or albuminous cells.

Development.— The sublingual gland is developed as a number of outgrowths 21 the buccal epithelium. These undergo ramifications, and subsequently

ome hollow.


Scalene Muscles and Subclavian Artery.

Scalene Muscles.—The scalene muscles 5 three.

Scalenus Anterior (Scalenus Anticus)—

igin .—By four short tapering tendons )m the anterior tubercles of the transrse processes of the third, fourth, fifth, d sixth cervical vertebrae.

Insertion .—The scalene tubercle of the st rib.

Nerve-supply .—The anterior primary mi of the fifth and sixth cervical nerves.

The muscle is directed downwards, itwards, and forwards.

Action .—To fix the first rib in ordinary spiration, and to elevate it in forced spiration; and to bend the neck to one le.

Chief Relations — Anterior. —The irenic nerve, which crosses the muscle diquely downwards and inwards; the ternal jugular vein, which lies in front of its origin; the subclavian iin close to its insertion; the thoracic or the right lymphatic duct;


Anterior.



A MANUAL OF ANATOMY


1236

the transverse cervical and suprascapular arteries; and the omo-hy muscle. Posterior. —The scalenus medius, with the intervention of second part of the subclavian artery, the nerve-roots of the bract plexus, and the cupola of the pleura. Medial. —The ascending cervi artery and the origin of the longus capitis.

Scalenus Medius — Origin. —By six short tapering tendons from posterior tubercles of the transverse processes of the lower six cervi vertebrae.

Insertion. —The upper surface of the first rib from the groove the subclavian artery backwards to the tubercle. Sometimes a i fibres are inserted into the suprapleural membrane (Sibson’s fasc over the cupola of the pleura. When distinct they are called 1 scalenus pleuralis.

Nerve-supply. —The anterior primary rami of cervical nerves fr the third to the eighth inclusive.

The muscle is directed downwards and outwards.

Action. —(1) To fix the first rib in ordinary inspiration, and (2) bend the neck to one side.

Relations — Anterior.— The cervical plexus, the nerve-roots of 1 brachial plexus, except the first thoracic, and the second and th parts of the subclavian artery. Posterior. —The levator scapulae a scalenus posterior muscles.

The scalenus medius is pierced by the following nerves: the nei to the rhomboids, which passes in a backward direction; and the up] and middle roots of the nerve to serratus anterior. These two roi usually emerge from the muscle as a single cord, and the lower or th root of the nerve descends in front of the scalenus medius, and jo the foregoing cord about the level of the first rib.

Scalenus Posterior (Scalenus Posticus) — Origin. —By two or th short tendons from the posterior tubercles of the transverse proces of the lower two or three cervical vertebrae.

Insertion. —The upper part of the outer surface of the second in front of the insertion of the highest slip of the serratus poster superior, and behind the origin of a portion of the first and the seco digitations of the serratus anterior.

Nerve-supply. —The anterior primary rami of the sixth, seven and eighth cervical nerves, the branches of which pass through 1 scalenus medius.

The muscle is directed downwards and outwards.

Action. —To elevate the second rib, and to extend the neck.

The scalenus posterior is the vestige of an important extensor muscle of neck in pronograde mammals, in which it is attached to several ribs. In orthograde position, however, with its balanced head, the need for it has ( appeared.

Relations — Anterior. —The scalenus medius. Posterior. —The lov two tendons of origin of the levator scapulae. The scalenus poster is intimately connected with the scalenus medius, of which it is pn tically a part.



THE HEAD AND NECK


1237


Subclavian Artery.—The right subclavian vessel arises from the )minate artery behind the right sterno-clavicular joint on a level 1 its upper part, and the left subclavian vessel arises from the >er aspect of the arch of the aorta towards its back part. On each the artery ends at the outer border of the first rib by becoming axillary artery. In its course the vessel is crossed superficially the scalenus anterior muscle, which divides it into three parts.


Rectus Capitis Anterior


Rectus Capitis Lateralis -

Basilar Part of Occipital Bone


Longus Capitis


Scalenus Posterior


Vertebral Artery (third part)


Scalenus Anterior. Scalenus Medius .


Longus Cervicis(upper oblique part) _Vertebral Artery (second part)


_Longus Cervicis (vertical part)


Vertebral Artery (first part)

HP. Longus Cervicis (lower oblique part)


Scalene Tubercle

Fig. 748. — The Right Prevertebral Muscles. The vertebral artery is also shown.


The first part extends from the origin of the vessel to the inner

der of the scalenus anterior; the second part lies behind that muscle;

I the third part extends from the outer border of the muscle to the ter border of the first rib. The. total length of the vessel on the ht side is about 3 inches, and on the left about 4 i inches. The ery describes an arch in front of the apex of the corresponding lg and pleura, and the height to which it rises above the clavicle

ibout inch.

First Part of the Right Subclavian Artery.—This part extends from i bifurcation of the innominate artery behind the light sterno








Fig. 749.—Right Subclavian Artery in situ: Jugular and Subclavia

Veins Removed.

ficially. The internal jugular and vertebral veins cross it from abc downwards close to the scalenus anterior, the latter vessel being belli the former, and the anterior jugular vein crosses it from within 0 wards, but superficial to the sterno-hyoid and sterno-thyroid muse] The vagus and its cervical cardiac branches, the cervical card branches of the sympathetic, and the nerve-loop known as the ai


1238


A MANUAL OF ANATOMY


clavicular joint, on a level with its upper part, to the inner border the scalenus anterior muscle. Its direction is upwards and out war and it lies very deeply.

Relations— Anterior .—The skin, superficial fascia and platysr deep cervical fascia, clavicular origin of the sterno-mastoid, and ster hyoid and sterno-thyroid muscles. Three veins are related to it sup







THE HEAD AND NECK


1239


. 750.—The Aorta in the Thorax, and the Principal Arteries of the

Head and Neck.


t. Arch of the Aorta Aortic Isthmus l- Aortic Spindle p Descending Aorta 5. Coronary Arteries (from Ascending Aorta)

5 . Innominate Artery 7 • Left Common Carotid 3 . Left Subclavian ?• Right Common Carotid


10. Right Subclavian

11. External Carotid

12. Internal Carotid

13. Maxillary

14. Superficial Temporal

15. Vertebral

16. Internal Mammary

17. Thyro-cervical Trunk

18. Inferior Thyroid

19. Transverse Cervical


20. Suprascapular

21. Superior Thyroid

22. Lingual

23. Facial

24. Occipital

25. Posterior Auricular

26. Ascending Pharyngeal

27. Transverse Facial

28. Posterior Iutercostals

29. Ligamentum Arteriosum







1240


A MANUAL OF ANATOMY


subclavia also cross it superficially. Posterior .—The recurrent lan geal nerve, sympathetic trunk, fat, longus cervicis muscle, first thora vertebra, cupola of the pleura, and apex of the lung. Inferior .—1 recurrent laryngeal nerve, part of the ansa subclavia, and the pleura

The right subclavian and right internal jugular veins unite in fr< of this part of the vessel to form the right innominate vein.

First Part of the Left Subclavian Artery.—This part extends fr< the upper aspect of the arch of the aorta, towards its back part, the inner border of the scalenus anterior muscle. It is therefore plac at first in the thoracic cavity. Its course is almost vertical until reaches the root of the neck, where it curves sharply outwards upon 1 cupola of the pleura, and so reaches the scalenus anterior. The re tions of the intrathoracic portion have been described in connect] with the thorax (see p. 1040).

Cervical Relations— Anterior .—The skin, superficial fascia a platysma, deep cervical fascia, clavicular origin of the sterno-masto sterno-hyoid, and sterno-thyroid muscles, and the thoracic duct whi arches over it. The left internal jugular and subclavian veins un

in front of it to form the left innomim vein, and the left vertebral vein descer in front of it under cover of the left interi jugular vein. Posterior .—The sympathe trunk with the inferior cervical ganglk fat, and the left longus cervicis muse Right. —The trachea, oesophagus, left : current laryngeal nerve, and thoracic du The varieties in origin of the subclavi artery have been described in connecti with the arch of the aorta (see p. 1040 seq.).

Second Part of the Subclavian Artery.

This portion of the vessel is situated behi the scalenus anterior muscle. It lies abo \ inch above the clavicle, and forms t highest part of the arch described by t vessel.

Relations— Anterior. — Its only din anterior relation is the scalenus anteri< Posterior .—The pleura. Superior. —T nerve-roots of the brachial plexus. 1 ferior .—The pleura.

In some cases the second part of the vessel passes through the scalenus ariter and in rare cases it passes in front of the muscle.


Fig. 751. —Left Subclavian Vessels and Terminal Piece of Thoracic Duct.


For the third part of the subclavian artery see p. 1191.


Development. —The right subclavian artery as far as the origin of the inter] mammary artery is developed from the fourth right aortic arch.

The left subclavian artery is developed from the seventh left, segmen arterv.





THE HEAD AND NECK


1241


Branches of the subclavian artery are the vertebral, internal nmary, thyro-cervical trunk, and superior intercostal. The first

e arise from the first part of the artery towards its termination, and

last arises from the second part on the right side, and from the

part on the left side.

Vertebral Artery. —This, the first branch on the right side, arises n the upper and back part of the artery about an inch from its ^n, and on the left side from the vessel just after it enters the root he neck. It passes for a short distance upwards, backwards, and htly outwards, and disappears from view by entering the foramen isversarium in the sixth cervical vertebra as a rule. It then ascends tically through the successive foramina transversaria above that of sixth vertebra, passing outwards between the axis and atlas, ving traversed the foramen transversarium of the atlas, it passes kwards and inwards, lying in vertebrarterial groove on the )er surface of the posterior arch the atlas behind the superior icular process, pierces the dura ter and arachnoid, and having ched the side of the spinal d, it turns upwards and forrds in the subarachnoid space,

I enters the cranial cavity ough the foramen magnum, gradually inclines from the eral to the ventral aspect of

medulla, and at the lower

rder of the pons it joins its low to form the basilar artery.

On account of its complicated arse, the vertebral artery is dded into four parts—namely, first or cervical, second or costoms verse, third or suboccipital, and fourth or intercranial.

The first part extends from the origin of the vessel to the foramen insversarium in the transverse process of the sixth cervical vertebra, lies between the scalenus anterior and longus cervicis muscles, ving the internal jugular and vertebral veins in front of it, being assed by the inferior thyroid artery, and having the sympathetic ank and the transverse process of the seventh cervical vertebra hind it. The vessel of the left side has the thoracic duct as an .ditional anterior relation.

The first part gives off no branches. . . .

The second part traverses the foramina transversaria ol the cervical

rtebrae from, as a rule, the sixth upwards. It is surrounded by t e
rtebral venous plexus, and by the vertebral plexus of the s}/mpaetic, and it lies in front of the cervical spinal neives as these emerge

3m the intervertebral foramina.





1242


A MANUAL OF ANATOMY


Branches.—These are as follows: spinal and muscular. T spinal branches enter the vertebral canal through the interverteb: foramina. The muscular branches supply the deep muscles of t neck, and anastomose with the deep cervical, ascending cervical, a occipital arteries.

For the third or suboccipital, and the fourth or intracranial, pai of the vertebral artery, see p. 1151.

Varieties. —(1) The left vertebral artery not uncommonly arises from the ai of the aorta between the origins of the left common carotid and left subclavi arteries. (2) The vessel may pass the foramen transversarium of the sh cervical vertebra, and may enter that of the fifth, or even that of the four (3) The vessel has been found in rare cases to enter the foramen transversarii of the seventh cervical vertebra.

Development. —The vertebral artery is developed from (1) the seventh cervi< somatic artery, and (2) the longitudinal anastomotic chain which connects f seven cervical somatic arteries.

Internal Mammary Artery.—This vessel, so named in contr

distinction to the external mammary, or lateral thoracic, a branch of t second part of the axillary artery, arises from the lower aspect of t' first part of the subclavian very nearly opposite the thyro-cervic trunk. Its course is downwards, forwards, and slightly inwards, ai it disappears behind the sternal end of the clavicle and first cost cartilage. For its subsequent course and relations, see p. 999.

Relations of Cervical Part— Anterior .—The clavicular part of tl sterno-mastoid, and the internal jugular and subclavian veins. Tl phrenic nerve crosses the vessel superficially from without inward Posterior .—The pleura.

No branches arise from this part of the vessel.

Thyro-cervical Trunk (Thyroid Axis).—This is a short trunk whi<; springs from the front of the first part of the subclavian artery clo to the inner border of the scalenus anterior muscle. It almost imm diately divides into three diverging branches—inferior thyroi transverse cervical, and suprascapular.

The inferior thyroid artery passes upwards and inwards in a tc tuous manner in front of the vertebral artery, and behind the carot sheath and sympathetic trunk, the middle cervical ganglion of whit often rests upon it. Having reached the lower part of the lobe of tl thyroid body, the artery breaks up into its terminal branches, whi< enter the lobe on its deep aspect, and ramify in it, anastomosing wi the superior thyroid and with its fellow of the opposite side of tl isthmus. As the vessel ascends it is intimately related to the recurre: laryngeal nerve, which usually lies behind it.

Branches.—These are as follows: muscular, ascending cervic; inferior laryngeal, tracheal, and oesophageal.

The muscular branches supply the scalenus anterior, longus cervic:: the infrahyoid muscles, and inferior constrictor of the pharynx. Tl ascending cervical artery arises from the inferior thyroid as it pass inwards behind the carotid sheath. It ascends in front of the trait verse processes of the cervical vertebrae, lying between the scalenj



THE HEAD AND NECK


1243


rior and longus capitis, and having the phrenic nerve on its outer and the sympathetic trunk just medial to it. It anastomoses branches of the vertebral, occipital, and ascending pharyngeal ries. It may furnish some spinal branches which enter the vertebral il through the intervertebral foramina to be distributed in a manner lar to the other spinal arteries. The inferior laryngeal artery impanies the recurrent laryngeal nerve to the larynx. The tracheal oesophageal branches are distributed as their names suggest, rhe transverse cervical artery passes transversely outwards in t of the scalenus anterior and phrenic nerve, and behind the icular part of the sterno-mastoid, lying a little above the clavicle, also above the suprascapular artery. It then enters the subdan triangle, which it soon leaves by passing deep to the inferior y of the omo-hyoid. It then passes in front of, or between, the ^e-trunks of the brachial plexus to the deep surface of the trapezius $cle. Having reached the anterior border of the levator scapulae, ivides into its two terminal branches—superficial and deep.

The superficial branch [superficial cervical artery) passes superficial the levator scapulae, and is distributed to the trapezius, levator pulae, splenius, and the adjacent lymph glands. The deep branch sterior scapular artery) passes backwards in front of the levator pulae to the superior angle of the scapula. It then descends along base of the bone, under cover of the rhomboid muscles, as far as inferior angle, where it anastomoses with the circumflex scapular 1 subscapular arteries. The artery gives branches to the adjacent iscles, and anterior and posterior branches to the scapula, which

e part in the scapular anastomoses proper (see p. 438).

The deep branch of the transverse cervical is frequently a branch the third part of the subclavian, in which cases there is no transverse vical artery, the superficial branch of the latter artery taking its ice and arising from the thyro-cervical trunk (see p. 1192).

The suprascapular artery passes downwards and outwards in front the scalenus anterior and phrenic nerve, and behind the clavicular rt of the sterno-mastoid. Having reached the back of the clavicle, courses outwards behind that bone, passing in front of the third rt of the subclavian artery and the trunks of the brachial plexus, then passes to the upper border of the scapula in company with the prascapular nerve. For the further course of the vessel and for the

ipular anastomoses of arteries see p. 441.

Branches in the neck are muscular, suprasternal, and nutrient, le muscular branches supply the sterno-mastoid and subclavius. le suprasternal branch descends over the inner end of the clavicle to pply the integument over the manubrium sterni. The nutrient tery of the clavicle is directed outwards, and enters the nutrient

ramen of that bone. It is often double.

Superior Intercostal Artery. —This vessel arises from the second irt of the subclavian on the right side, and from the first part on le left side, in each case from the posterior aspect of the paient


i 2 4 4


A MANUAL OF ANATOMY


trunk. On the right side it is therefore behind the scalenus anter and on the left side close to the inner border of that muscle. ' vessel at first passes backwards and upwards for a short distance, ; then descends in front of the neck of the first rib. At the postei extremity of the first intercostal space it furnishes the first postei intercostal artery to that space, and then descends in front of neck of the second rib to become the second posterior intercom artery. The superior intercostal artery therefore furnishes the fi and second posterior intercostal arteries for the first and second inf costal spaces, their distribution being similar to that of the succeed posterior (aortic) intercostal arteries. Besides these two brand: the vessel gives off the deep cervical artery. This branch, which homologous with the posterior branch of a posterior intercostal arte arises from the superior intercostal before it descends in front of 1 neck of the first rib.

The superior intercostal artery and the deep cervical art< are often described as terminal branches of a common trunk origin. This trunk is called the costo-cervical trunk; in 1 description adopted here this trunk is looked on as part of f superior intercostal itself.

It passes backwards between the transverse process of the sever cervical vertebra and the neck of the first rib, and then ascends betwe the semispinalis capitis and semispinalis cervicis muscles to about f level of the axis. In this situation it anastomoses with the de division of the descending branch of the occipital artery. The de cervical in its course gives off muscular branches which anastomc with branches of the vertebral and ascending cervical arteries, also furnishes a spinal branch which enters the vertebral canal throu the intervertebral foramen between the seventh cervical and fii thoracic vertebrae.

The superior intercostal artery on each side is developed from the anast< motic loop between the upper two or three thoracic somatic arteries.

Subclavian Vein. —This vessel, which is the direct continuation the axillary vein, extends from the outer border of the first rib to t back of the inner end of the clavicle, where it unites with the intern jugular to form the innominate vein. It lies in front of, and on lower plane than, the subclavian artery, and it passes in front of t scalenus anterior muscle and phrenic nerve. In rare cases the ve has been met with passing behind the scalenus anterior. Its princip tributary is the external jugular vein (sometimes also the anteri jugular). The external jugular vein joins it close to the outer bord of the sterno-mastoid.

The thoracic duct opens at the angle of junction of the left su clavian and left internal jugular veins, and the right lymphatic du opens into the angle of junction of the corresponding veins on t] right side. The duct often opens in two or more parts.

Vertebral Vein. —This vein begins in the suboccipital veno


THE HEAD AND NECK


1245


ms within the suboccipital triangle. It passes through the foramen lsversarium in the atlas, and accompanies the vertebral artery nigh the succeeding foramina transversaria as low as the sixth, ning a plexus around the vessel. This plexus is ultimately replaced a single vein, which emerges through the foramen transversarium he sixth cervical vertebra (sometimes the seventh). It then descends ront of the first part of the subclavian artery under cover of the irnal jugular vein, and opens into the back part of the innominate 1, the opening being provided with a single or double valve.

The chief tributaries of the vertebral vein are as follows: muscular, lal, anterior vertebral, and deep cervical. It also, as a rule, dves the first intercostal vein.

No vein accompanies the ceral part of the internal mamry artery. The inferior thyroid a, which does not accompany corresponding artery, is found cribed in connection with the Toid gland on p. 1222.

The transverse cervical and irascapular veins return the od from the parts supplied by i corresponding arteries, and tributaries of the lower part the external jugular vein.

The deep cervical vein starts the suboccipital venous plexus

Tin the suboccipital triangle. ^ 0

descends in company with the Fk, 753-^*^^™ V*™ 'P cervical artery, and passes . , ,, ,•

  • J xr Anterior jugular frequently opens di

rectly into subclavian vein. Vertebral vein," which receives superior intercostal, opens into beginning of innominate.


INNOM,


wards between the transverse •cess of the seventh cervical tebra and the neck of the first to terminate in the vertebral


rhe anterior vertebral vein begins in a plexus in front of the uppei ical transverse processes. It descends in company with the nding cervical branch of the inferior thyroid artery receiving cular tributaries in its descent, and it opens into the lower part

Jollateral^irculation after Ligature of the Third Part of the Subian Artery.— (i) The suprascapular and the deep branch of the sverse cervical, both branches of the thyro-cervical trunk fiom part of the subclavian, take part in the scapular anastomoses and stomose freely with branches of the first and t rr par s 0 e lary artery. (2) The internal mammary from the first part of subclavian anastomoses with the lateral thoracic from the second

of the axillary.



1246


A MANUAL OF ANATOMY


Collateral Circulation after Occlusion of the First Part of Subclavian Artery. —(1) The vertebral artery of one side anastomc with that of the opposite side. (2) The internal mammary anas moses with the inferior epigastric from the external iliac, and w the posterior intercostal arteries. (3) The inferior thyroid anas moses with the superior thyroid from the external carotid. (4) 1 superior intercostal anastomoses with the third posterior intercosi (5) The deep cervical of the superior intercostal anastomoses with deep division of the descending branch of the occipital from the exter carotid. (6) The scapular branches of the thyro-cervical trr anastomose with branches of the axillary artery. (7) The thora branches of the axillary artery anastomose with the posterior ini costals.

Cervical Part of the Thoracic Duct (Fig. 751). — This part of 1 thoracic duct occupies the root of the neck on the left side, and ] upon the side of the oesophagus, between it and the left subclav: arteries. In this position it ascends to about the level of the sevei cervical vertebra, and then it describes a curve and passes outwar forwards, and downwards in contact with the cupola of the left pleu It then inclines inwards, and, after receiving the left jugular and si clavian trunks, ends in the angle of junction of the internal jugu and subclavian veins of the left side. The terminal orifice of the di is guarded by a valve composed of two segments, which are so direcl as to effectually prevent the reflux of chyle and the flow of blood ii it. The duct crosses the left vertebral artery, passing either in frc of or behind the vertebral vein. In half the cases the duct is dou' for some distance before it enters the internal jugular, and one brar may open into the subclavian vein. Occasionally three or m< openings have been found, and this multiple opening is of surgi importance, for if one branch is cut in an operation on the root of i neck, it is an even chance that there may be another to carry t chyle to the blood-stream. It is important to notice that the di passes behind the vagus and in front of the phrenic nerves.

Right Lymphatic Duct. —The position of this duct corresponds that of the thoracic duct on the left side. It is about inch in lengi and is formed by the union of the right subclavian trunk and rig jugular trunk. Besides returning lymph from the right side of t head and neck and the right upper limb, it receives the lympha vessels from the right side of the heart, the right lung, the upp part of the right half of the thoracic wall, and some of those from t antero-superior surface of the liver. It ends in the angle of juncti of the internal jugular and subclavian veins of the corresponding sic its orifice being guarded by a double valve.

Cervical Portion of the Lung. —The apex of the lung projects in the root of the neck as high as the neck of the first rib. It is cover by the cupola of the pleura, on the inner and anterior aspects of whi the subclavian artery arches outwards. The cupola of the pleura covered by the suprapleural membrane (Sibson’s fascia), which exten


THE HEAD AND NECK


1247


im the medial border of the first rib to the front of the transverse Dcess of the seventh cervical vertebra. This membrane is probably rived from the adjacent scalene muscles, and it may contain some iscular fibres.


The Contents of the Orbit.

The following structures are found in the orbit:

Orbital Fascia. —The periosteum of the orbit is continuous posteriorly th the dura mater through the superior orbital fissure, and constitutes 0 orbital fascia. Anteriorly it becomes continuous with the periinium of the frontal bone, and the periosteum of the maxilla and gomatic bones. Along the supra-orbital and infra-orbital margins 0 superior and inferior palpebral fascia0 blend with it. The orbital >cia is loosely attached to the bony walls of the orbit, and forms a 0ath for the contents of the cavity, which is incomplete in front. Lacrimal Gland. —This gland lies at the anterior and outer part the orbit superiorly, where it occupies the lacrimal fossa on the ler side of the zygomatic process of the frontal bone. It is discaped. Its upper surface is convex, and its under surface is conve in adaptation to the eyeball. The anterior part of the gland is rtly cut off by the outer edge of the levator palpebrae superioris, d is known as the palpebral portion , the chief part being known the orbital portion . The ducts, which issue from both portions, 0 about twelve in number, and they open in a row into the outer part the superior conjunctival fornix.

Blood-supply. —The lacrimal artery.

Nerve-supply. —The lacrimal nerve and sympathetic filaments.

The structure of the gland is something like to that of the parotid. Development. —The lacrimal gland, like the tarsal and ciliary glands, is /eloped as solid epithelial cords from the conjunctiva. These epithelial 'ds spring from the upper and outer part of the conjunctiva, where it is rented from the inner surface of the upper eyelid on to the front of the eyeball, e solid cords grow into the neighbouring mesoderm, and give off lateral proses. Cords and processes, at first solid, soon become hollow, and so give 3 to the alveoli, or acini, and ducts of the lacrimal gland.

In reptiles the ducts open all round the fornix of the conjunctiva, but in unmals only the upper and outer ones persist.

Muscles.— These are the levator palpebrae superioris, rectus superior,

tus inferior, rectus medialis, rectus lateralis, obliquus superior, and

liquus inferior.

Levator Palpebrae Superioris — Origin. —The under surface of the of of the orbit above, in front of, and medial to the optic foramen. Insertion. —By a broad membranous expansion, which divides into ree tendinous laminae. The middle lamina, which is the chief serf ion, and consists largely of involuntary muscular fibres, is attached the upper margin of the superior tarsus. The upper or superficial yer, which is fibrous, passes in front of the superior tarsus, lying tween it and the palpebral fibres of the orbicularis oculi. Its fibres


1248


A MANUAL OF ANATOMY


pierce the superior palpebral fascia, and, having passed between bundles of the palpebral portion of the orbicularis oculi, they attached to the skin of the upper eyelid. The lower or deep layer , wl is also fibrous, is attached to the conjunctiva along the superior for


Supra-orbital Nerve (in two divisions)


Supratrochlear Nerve Infratrochlear Nerve S™


Olfactory Bulb


Naso-ciliary Nerve


Optic Nerve-


Frontal Nerve on Levator Palpebrae Superioris

Lacrimal Nerve passing along Rectus Lateralis


Ophthalmic Artery’-'

Oculo-motor Nerve"*

Trochlear Nerve'

Abducent Nerve-'

Motor Root of Trigeminal Nerve

Fig. 754. —Dissection of the Orbit from above (Hirschfeld and Leveil


Maxillary Nerve Ophthalmic Nerve 7 Mandibular Nerve '-Trigeminal Ganglion

'•Sensory Root of Trigeminal Nerve


The outer and inner margins of the broad membranous expans are attached to the outer and inner margins of the orbit close to lateral and medial palpebral ligaments, and at the inner angle a < is attached to the pulley of the obliquus superior.

Nerve-supply .—The 1 per division of the th cranial nerve, the brai from which enters the d< or ocular surface of muscle near its ori£ having pierced the rec superior.

Action .—To raise upper eyelid. The mus is the antagonist of superior palpebral fibres the orbicularis oculi.

The levator palpebrse is a delamination of the rectus superior, to whicl is so closely attached that, even when it is paralyzed, the upper lid may raised a little by looking upwards.

Relations. — Superiorly , the frontal nerve and the supra-orbi artery. Inferiorly , the rectus superior and the conjunctiva.


WHICH MOVE THE EYEBALL.














THE HEAD AND NECK


1249

Recti Muscles Rectus Superior— Origin. —The upper part of the rnmon tendinous ring in relation to the optic foramen.

Insertion. By a thin expanded tendon into the upper surface of e sclera about three or four lines from the margin of the cornea. Nerve-supply.-' The upper division of the oculo-motor nerve, the anch from which enters the deep or ocular surface of the muscle ar its origin.

The muscle is flattened from above downwards, and its direction forwards and slightly outwards.

The actions of the muscles of the eyeball are considered together tp- 1251 Relations.' Superiorly , the levator palpebrae superioris, which is e narrower of the two muscles. Inferiorly , the tendon of the obliquus penor, the eyeball, and the soft fat of the orbit.

Rectus Medialis (Internal Rectus)— Origin. —The inner part of the mmon tendinous ring in relation to the optic foramen, the origin

ing wide.

Insertion. By a thin expanded tendon into the inner surface of e sclera about three or four lines from the margin of the cornea. Nerve-supply. —The lower division of the oculo-motor nerve, the anch from which enters the deep or ocular surface of the muscle.

The muscle is flattened from within outwards, and its borders are perior and inferior. Its direction is almost straight forwards.

Relations.—Above the upper border of the muscle is the obliquus perior, and between the two the naso-ciliary nerve and the anterior id posterior ethmoidal vessels pass.

Rectus Inferior— Origin. —The lower part of the common tendinous ig in relation to the optic foramen.

Insertion. —By a thin expanded tendon into the lower surface the sclera about three or four lines from the margin of the rnea.

Nerve-supply. —The lower division of the oculo-motor nerve, the anch from which enters the deep or ocular surface of the muscle.

The muscle is flattened from above downwards, and its direction forwards and slightly outwards.

Relations— Inferior. —A part of the obliquus inferior.

Rectus Lateralis (External Rectus)— Origin. —This muscle arises bv [0 heads. y

Inferior Head.—(1) The lower part of the common tendinous ring relation to the optic foramen, where it is near the rectus inferior; d (2) the prominent spine on the lower margin of the superior orbital sure near its inner end.

Superior Head.—The outer portion of the upper part of the common idinous ring in relation to the optic foramen, where it is above 2 superior orbital fissure, external to the optic foramen, and near - rectus superior. The two heads are connected by a tendinous nd which arches over the superior orbital fissure, and gives origin some of the fibres of the inferior head of the muscle.


79



1250


A MANUAL OF ANATOMY


Insertion. —The outer surface of the sclera from three to four li from the margin of the cornea.

Nerve-supply. —The abducent nerve, the branches of which en the deep or ocular surface of the muscle.

The muscle is flattened from without inwards, and its directioi forwards and outwards.

Action. —To abduct the eyeball, so as to direct the cornea outwai

Relations.—The following structures pass between the two he of the muscle in order from above downwards: (i) the upper divis of the oculo-motor nerve; (2) the naso-ciliary nerve; (3) the hr division of the oculo-motor nerve; (4) the abducent nerve; and (5) superior ophthalmic vein or veins.

Common Tendinous Ring of the Recti Muscles.—This tendon ta the form of a fibrous ring, which is attached to the upper, inner, ; lower margins of the optic foramen. It then crosses transvers the inner portion of the superior orbital fissure to a prominent sp on the lower margin of that fissure near its inner end. From 1 spine it recrosses the superior orbital fissure in a vertical direct near its centre, and finally reaches the upper part of the optic foram This latter portion gives origin to some fibres of the inferior head the rectus lateralis. The upper part of the ring is sometimes knc as the tendon of Lockwood , and gives origin from within outwa to part of the rectus medialis, the rectus superior, and the supei head of the rectus laterals. The lower part is also sometimes ca]

the ligament of Zinn y which gives ori from within outwards to part of the rec medialis, the rectus inferior, and the infei head of the rectus lateralis.

Obliqui Muscles — Obliquus Superio: Origin. —The wall of the orbit directly front of the upper and inner part of optic foramen, close to the recti superio] medialis.

Insertion. —By an expanded tendon i the upper and outer aspect of the sc] just beyond the outer border of the supe: rectus, and midway between the margir the cornea and the entrance of the oj nerve.

The muscle is situated at the upper 1 inner part of the orbit, internal to levator palpebrae superioris. It is directed forwards towards inner angle of the orbit, on approaching which it ends in a sr round tendon. This tendon passes through a fibro-cartilagin pulley close to the medial angular process of the frontal bone, then changes its direction, and passes downwards, outwards, ; backwards beneath the tendon of the rectus superior to reach insertion just lateral to that tendon.


Fig. 756.—The Superior Oblique Muscle.




THE HEAD AND NECK


1251

The fibro-cartilaginous pulley or trochlea is attached by fibrous

sue to the trochlear fossa on the orbital plate of the frontal bone

)se to the medial angular process. It is lined with synovial membrane lubricate the tendon and facilitate its movement at this abrupt ange in its course. The tendon receives a fibrous investment from e outer margin of the pulley.

Nerve-supply.—The trochlear nerve, which enters the muscle on

superficial or orbital surface near its origin.

Relations— Superior. —The roof of the orbit and the rectus superior. ferior. —The upper border of the rectus medialis, having the nasoiary nerve and the anterior and posterior ethmoidal vessels between em. Lateraf^—-The levator palpebrae superioris.

Obliquus Snpemr — Origin. —A small depression at the anterior and tier part of the floor of the orbit immediately lateral to the upper >ening of the lacrimal canal.

Insertion. —The outer surface of the sclera under cover of the rectus teralis, and slightly posterior to the level of the insertion of the iliquus superior.

Nerve-supply— The lower division of the oculo-motor nerve, the anch of which is long and enters the posterior border of the muscle. The muscle at first passes outwards and backwards upon the floor the orbit beneath the rectus inferior, and then it turns upwards itween the sclera and the rectus lateralis, where its tendon expands lore its insertion.

Relations. —Towards the eyeball the muscle is related to the ctus inferior and the sclera, and towards the orbit to the floor of e cavity and the rectus lateralis. The borders of the muscle are Lterior and posterior, the latter, as stated, receiving the nerve ppiy Movements of the Eyeball. —The movements of the eyeball con>t of rotation round a point situated just behind the centre of its hero-posterior axis. When the eyeball rotates round its vertical

is, horizontal or lateral movements take place, and the cornea

directed outwards or inwards according to the muscle which acts. ie rectus lateralis abducts the eyeball, so as to direct the cornea itwards, and the rectus medialis adducts the eyeball, so as to rect the cornea inwards. When the eyeball rotates round its trans;rse axis vertical or upward and downward movements take place, id the cornea is directed upwards or downwards according to the uscle which acts. The rectus superior elevates the eyeball, and e rectus inferior depresses it. It is to be borne in mind, however, at these two muscles in passing forwards have each a slight innation outwards. Whilst, then, they respectively elevate and depress e cornea on the transverse axis of the eyeball, each of them also ^es it a certain amount of inward movement on the vertical axis, companied by slight rotation on the antero-posterior axis. In e case of the rectus superior this inward and rotatory movement corrected by the obliquus inferior acting in association with it, and



1252


A MANUAL OF ANATOMY


in the case of the inferior rectus by the obliquus superior acting association with it.

Direct elevation of the eyeball is therefore effected by the re< superior, aided by the obliquus inferior, and direct depression of eyeball is effected by the rectus inferior, aided by the obliquus supei The superior oblique, acting alone, would depress the cornea abduct it, making the eye look downwards and outwards, and obliquus inferior, acting alone, would elevate and abduct it, tl movements in each case being accompanied by slight rotation on antero-posterior axis.

Fascia of the Orbit.—This fascia forms (i) the fascial sheath


the eyeball, fascia bulbi; and (2) sheaths for the ocular muscles.

The fascia bulbi is practically the thickened wall of a lyn space round the sclerotic coat of the eyeball, and extends from

point of entrance of the o]


nerve to near the margin of cornea. Posteriorly it is perfora by the ciliary vessels and ner and blends with the dura ma sheath of the optic nerve, ; anteriorly it fades away when meets the ocular conjunctiva, outer surface of the capsule h contact with the orbital fat, ; anteriorly with the ocular c junctiva. The fascial sheath (c sule of Tenon) forms a cavity socket, within which the eyel glides with perfect freedom fr friction.

The lower part of the fas< sheath of the eyeball is said to thickened by the suspensory li ment of the eye (Lockwood). This is attached laterally to Whitna tubercle on the zygomatic bone, and medially to the lacrimal bo It is expanded beneath the eyeball, to the fore part of which it a as a sling or support.

The muscular sheaths are derived from the fascial sheath of eyeball. The tendons of the six ocular muscles pierce the fas( sheath on their way to their insertions, which latter are under cover the fascial sheath, each muscle receiving a prolongation from the mar ; of the cleft in the sheath through which its tendon passes. Th prolongations extend backwards around the muscles, and ultimat blend with their perimysial sheaths. As regards the obliquus super muscle, the prolongation around its tendon extends upwards, inwar and forwards as far as the margin of the pulley, to which it is attach The prolongation around the tendon of the obliquus inferior mus extends downwards as far as the outer part of the floor of the orbit


It has an endothelial lining (dotted line) which is reflected along the tendons to their insertions; the fibrous basis is reflected back towards the muscle.



THE HEAD AND NECK


1253


The sheaths of the four recti muscles give off important expanms. The expansion from the sheath of the rectus lateralis is strong, id is attached to the frontal process of the zygomatic bone, and at from the sheath of the rectus medialis, also strong, is attached the lacrimal crest of the lacrimal bone. These two expansions their bony attachments are connected with the lateral extremities the suspensory ligament of the eye. The expansion from the eath of the rectus superior blends with the deep layer of the tendon the levator palpebrae superioris, and that from the sheath of the

tus inferior is connected with the inferior tarsus. These expansions

>m the sheaths of the recti, especially from those of the recti lateralis medialis, moderate the action of the muscles, and the latter two e hence known as the check ligaments.

Nerves in the Orbit—Optic Nerve.—The optic nerve extends forirds and outwards from the optic chiasma, and enters the orbit rough the optic foramen, having the ophthalmic artery below it first, and then on its outer side. It receives sheaths from the ira mater and arachnoid, the former being strong, and at its entrance to the orbit it is surrounded by the origins of the four recti muscles.

? direction is forwards and outwards, with a slight inclination wnwards, to the back part of the eyeball, where it pierces the sclera out inch medial to, and a little below, the centre. It then pierces e choroid coat, and ends in the nerve-fibre layer of the retina. The iary ganglion is close to the outer side of the nerve towards the back rt of the orbit, and in front of this the nerve is surrounded by the iary nerves and vessels. It is crossed superiorly by the ophthalmic tery, the superior ophthalmic vein, and the naso-ciliary nerve, feriorly, about J inch behind the eyeball, the central artery of the tina enters it and then runs forward within it to the retina.

Third or Oculo-motor Nerve.—This nerve, having left the outer dl of the cavernous sinus, breaks up at the superior orbital fissure into 0 divisions, upper and lower. These enter the orbit between the 0 heads of the rectus lateralis muscle, the naso-ciliary nerve being uated between the two.

The superior division enters the deep surface of the rectus superior pplying it, after which it pierces the muscle and ends in the levator lpebrae superioris.

The inferior division, larger than the upper, has three branches, lich supply the rectus medialis, the rectus inferior, and the obliquus hrior. The twigs to the recti medialis et inferior enter these muscles their deep or ocular surfaces. The branch to the obliquus inferior a long nerve which passes forwards between the recti inferior et eralis, and its twigs enter the obliquus inferior muscle at its posterior 'der. Posteriorly it furnishes the ganglionic branch, which forms the 3 rt or parasympathetic root of the ciliary ganglion.

The fourth, trochlear, or pathetic nerve, of small size, having left 2 wall of the cavernous sinus, enters the orbit through the superior sital fissure above the muscles, and medial to, but on a slightly


I2 54


A MANUAL OF ANATOMY


higher plane than, the frontal nerve. Having passed inwards o 1 the levator palpebrae superioris, it enters the posterior part of the ol quus superior muscle on its superficial or orbital surface, this bei the only muscle which it supplies.

The sixth or abducent nerve, having left the cavernous sinus, ent the orbit through the superior orbital fissure, and passes between 1

two heads of the rectus lateralis muscle, this situation it has the lower division of 1 oculo-motor nerve above it, and the super ophthalmic veins below it. It supplies 1 rectus lateralis, its twigs entering the mus on its deep or ocular surface.

Branches of the Ophthalmic Division of I Trigeminal Nerve. — The ophthalmic ner having left the outer wall of the cavernc sinus, and before reaching the superior orbi fissure, divides into frontal, lacrimal, a naso-ciliary nerves.

The frontal nerve, of large size, enters 1 orbit through the superior orbital fissure abc the muscles. In this situation it has the 1; rimal nerve lateral to, and on the same pla with it, and the trochlear nerve medial to but on a slightly higher plane. It then pas: forwards on the upper surface of the levai palpebrae superioris, underneath the periostei of the roof of the orbit, and before arrivi at the supra-orbital margin it divides into t branches, supra-orbital and supratrochlear.

The supra-orbital nerve, which in size a direction is the continuation of the front passes forwards to the supra-orbital notch foramen, through which it leaves the orbit company with the supra-orbital artery. ( the forehead it divides into two branches, late and medial, which have been already descrit (see p. 1153). Sometimes this division takes place within the ort and in these cases the inner branch usually passes through the sup: orbital notch.

The supratrochlear nerve, of small size, passes forwards and inwai to the pulley to the obliquus superior muscle, above which it runs the forehead, where it has been already described (see p. 1154)- Bef( leaving the orbit it gives off a small twig, which passes downwar close to the pulley of the obliquus superior, to form a loop with i infratrochlear branch of the naso-ciliary nerve.

The lacrimal nerve enters the orbit through the superior orbi fissure above the muscles, and external to the frontal nerve. It tt passes forwards and outwards along the upper border of the rec


Fig. 758. —The Third and Sixth Cranial Nerves in the Orbit .


I.O., nerve to inferior oblique; other branches running directly forward from lower division of the third nerve are going to inferior rectus.








THE HEAD AND NECK


1255


eralis in company with the lacrimal artery. On reaching the lacrimal

md it gives numerous branches to its deep surface, and is then coniued through the orbital septum to the skin and conjunctiva of the ter part of the upper eyelid, and the skin in the region of the zygoitic process of the frontal bone. Near the lacrimal gland it sends wnwards a small twig, which joins the zygomatico-temporal nerve. The naso-ciliary nerve (nasal nerve) is more deeply placed than the rntal and lacrimal. It enters the orbit through the superior orbital sure, and passes between the two heads of the rectus lateralis muscle, [ng between the upper and lower divisions of the oculo-motor nerve, then passes obliquely inwards and forwards to the inner wall of the bit, lying beneath the rectus superior and above the optic nerve, d, later on, between the obliquus superior and the rectus medialis. iving reached the inner wall of the orbit at the anterior ethmoidal


g. 759- —Scheme of the Distribution of the Oculo-motor, Trochlear,

and Abducent Nerves (Flower).

f U - D - { L rJ: Sg2£sSKZ" SUPeri ° riS

! rR.Int. Rectus Medialis

Oculo-Motor Nerve ' L.D. Lower Division -j R.Inf. Rectus Inferior

( O.I. Obliquus Inferior


C.G. Ciliary Ganglion ^ M.R. Motor Root

S.R. Sensory Root (from Naso-ciliary Nerve) Sy.R. Sympathetic Root S.C. Short Ciliary Nerves Trochlear Nerve—O.S. Obliquus Superior Abducent Nerve—R.E. Rectus Lateralis.


ramen, it parts with its infratrochlear branch, and then passes through e foramen in company with the anterior ethmoidal artery, and so iters the anterior fossa of the base of the skull. It then passes forwards id inwards in a groove on the upper surface of the cribriform plate the ethmoid bone, lying under cover of the dura mater. Having ached the nasal slit at the side of the fore part of the crista galli, descends through this slit, or through a small foramen just in front it, into the nasal cavity, and immediately gives off two internal nasal anches. Then the nerve descends in a groove on the posterior surface the nasal bone, giving offsets to the mucous membrane of the outer all of the nasal cavity in front of the superior and middle nasal •nchae. Finally, the nerve comes out, as the external nasal branch, dween the lower border of the nasal bone and the upper nasal cartilage, id supplies the skin of the tip and lower part of the side of the nose.






A MANUAL OF ANATOMY


1:256

In connection with this remarkable course of the nerve it is to t noted that it is to be met with in four different regions—name! (1) in the orbit; (2) on the cribriform plate of the ethmoid bone : the anterior cranial fossa; (3) in the nasal cavity; and (4) on the fa< in the region of the tip of the nose.

Branches. —The ramus communicans to the ciliary ganglion forms tl long or sensory root of that ganglion. It is slender, about ^ inch Ion and arises from the naso-ciliary as it passes between the two hea( of the rectus lateralis. It enters the ciliary ganglion at its poster superior angle.

The long ciliary nerves , usually two in number, arise from tl naso-ciliary immediately after it has crossed the optic nerve, and the


Supra-orbital Nerve (in two divisions)


Supratrochlear Nerve—: In fra trochlear Naso-ciliary—'


Olfactory Bulb Naso-ciliary Nerved


Optic Nerve—

?

Ophthalmic Artery — Oculo-motor Nerve- - """


Trochlear Nerve


-•Frontal Nerve on Levator Palpebrae Superioris


    • • Lacrimal Nerve passing along

Rectus Lateralis


~ Maxillary Nerve Ar Ophthalmic Nerve

      • Mandibular Nerve

'.Trigeminal Ganglion

Abducent Nerve"' j ,,v ‘ Sensory Root of Trigeminal Nerve

Motor Root of Trigeminal Nerve

Fig. 760. —Dissection of the Orbit from above (Hirschfeld and

Leveille) .


communicate with the short ciliary nerves from the ciliary ganglioi which they accompany to the back part of the sclera. Here they pierc the sclera, and are distributed along with the short ciliary nerves.

The infratrochlear nerve arises from the naso-ciliary close to th anterior ethmoidal foramen, and passes forwards beneath the obliqur superior muscle. Near the pulley of that muscle it receives a twi from the supratrochlear nerve, and then, passing beneath the puller it leaves the orbit at the medial angle to be distributed to the ski and conjunctiva of the inner parts of the eyelids, the side of the roc of the nose, the lacrimal sac, and the caruncula lacrimalis.

As the nerve traverses the anterior ethmoidal canal it gives twig to the mucous membrane of the frontal sinus and of the anterior etl moidal sinus.






THE HEAD AND NECK


1257


A posterior ethmoidal nerve is described as passing through the isterior ethmoidal canal to supply the mucous membrane of the jsterior ethmoidal sinus and of the sphenoidal sinus.

For the branches of the naso-ciliarv nerve to the exterior of the nose id to the nasal fossa, see p. 1276.

Ciliary Ganglion (Lenticular Ganglion).—This is a small quadriteral body, about the size of a moderately large pin-head, which is

uated in the posterior part of the orbit, where it lies flattened upon

e outer side of the optic nerve. It is usually in close contact with


A



Fig. 761.—A, The Ciliary Ganglion; B, The Nerves of the Orbit (Lateral Aspect) (Hirschfeld and Leveille).


lternal Carotid Plexus phthalmic Nerve aso-ciliary Nerve ympathetic Root of Ciliary Ganglion


rigeminal Ganglion 'culo-motor Nerve bducent Nerve lternal Carotid Artery ptic Nerve

ommon Tendinous Ring for Recti


A

5. Sensory Root of Ciliary Gang lion

6. Long Ciliary Nerves

7. Branch of Oculo-motor Nerve

to Obliquus Inferior

B

7. Levator Palpebrae Superioris

8. Rectus Superior

9. Frontal Nerve

10. Rectus Lateralis

11. Obliquus Superior

12. Rectus Inferior

13. Short Ciliary Nerves


8. Motor Root of Ciliary Ganglion

9. Ciliary Ganglion

10. Infratrochlear Branch of Naso ciliary Nerve

11. Short Ciliary Nerves


14. Branch of Oculo-motor Nerve to

Obliquus Inferior

15. Ciliary Ganglion

16. Ophthalmic Nerve

17. Maxillary Nerve

18. Mandibular Nerve


it nerve, and is recognized by its reddish-pink colour. Posteriorly receives its three roots, and anteriorly the short ciliary nerves pass wards from it. The roots are called sensory, motor, and sympathetic, e sensory root is derived from the naso-ciliary nerve as it passes

ween the two heads of the rectus lateralis. It is slender, about

nch long, and enters the postero-superior angle of the ganglion, e motor root is derived from the long branch of the lower division the oculo-motor nerve which supplies the obliquus inferior muscle, 1 it enters the postero-inferior angle of the ganglion. The sym









1258


A MANUAL OF ANATOMY


pathetic root is a very minute nerve which is derived from the interi carotid plexus of the sympathetic, and it usually reaches the gangli in company with the sensory root. It may, however, join the gangli separately, and then it does so in close proximity to the entrance the long root.

The branches of the ciliary ganglion are called the short cilic, nerves. They are from six to eight in number, and come off in b groups from the antero-superior and antero-inferior angles. T nerves of the lower group usually exceed those of the upper in numb As they pass forward above and below the optic nerve they divide, a give rise to from sixteen to twenty delicate filaments. Having reach the back of the eyeball, they pierce the sclera around the entrar of the optic nerve. They then pass forwards between the sclera a


Infratrochlear Artery Medial Palpebral Arteries


Dorsal Nasal Artery-— Pulley of Obliquus Oblique-.


Anterior Ethmoidal Artery.

Posterior Ethmoidal Artery..


Central Artery of the Retina (in outline)

Obliquus Superior Rectus Superior (cut)

Levator Palpebra? Superioris (cut)


Optic Nerve Optic Chiasma (right half)


Lacrimal Gland


Supra-orbital Artery


Long Posterior Ciliary Arteries

Lacrimal Artery


Rectus Lateralis (cut) Ophthalmic Artery


Right Optic Tract

Fig. 762. —Dissection of the Right Orbit from above, showing the Op Nerve, Ophthalmic Artery, and Superior Oblique Muscle.


the choroid, giving twigs to the latter, and they are finally distribul to the ciliary muscle, the iris, and the cornea. The short cilic nerves thus convey co the eyeball sensory fibres from the ophthalr division of the trigeminal nerve, motor fibres from the oculo-mo nerve, and sympathetic fibres from the internal carotid plexus of 1 sympathetic.

Summary of the Ophthalmic Nerve. —This nerve is entirely sensory, supplies (1) the skin of (a) the frontal region and top of the skull; (&) the up eyelid, and (c) the root, tip, and lower part of the side of the nose; (2) the cari cula lacrimalis and lacrimal sac; (3) the mucous membrane of the nasal cavi and the conjunctiva; (4) the eyeball; and (5) the lacrimal gland.

Summary of the Ciliary Ganglion. —The branches of this ganglion supply 1 cornea, iris, and ciliary muscle. The fibres which supply the sphincter pUpi are derived from the oculo-motor nerve by means of the motor root of the gangli





THE HEAD AND NECK


1259


le fibres which supply the dilator pupillse are derived from the sympathetic by eans of the sympathetic root of the ganglion, which is derived from the internal rotid sympathetic plexus.


Branch of the Maxillary Division of the Trigeminal Nerve.—The rgomatic nerve (temporo-malar nerve), of small size, arises from the axillary in the pterygo-palatine fossa. It enters the orbit through Le inferior orbital fissure, and soon divides into two branches, zygoatico-temporal and zygomatico-facial. The zygomatico-temporal nerve imp oral branch) ascends upon the outer wall of the orbit, and, having ceived a communicating twig from the lacrimal nerve, it leaves the ivity by passing through the zygomatico-temporal canal in the rgomatic bone. Its destination is the skin of the anterior part of Le temporal region.


Medial Palpebral Arteries Supratrochlear Artery


Dorsal Nasal Artery


Anterior Ethmoidal Artery


Posterior Ethmoidal Artery Ophthalmic Artery

Posterior Ciliary Arteries Ophthalmic Artery (in Optic Foramen)


Lacrimal Gland


-\ Lateral Palpebral . j Arteries


Supra-orbital Artery


Lacrimal Artery

- Muscular Arteries Arteria Centralis Retinae '■ Posterior Ciliary Arteries

— Internal Carotid Artery


Fig. 763. —Diagram of the Ophthalmic Artery and its Branches.


The zygomatico-facial nerve [malar branch ) passes forwards in the lgle between the outer wall and floor of the orbit, and leaves the vity by passing through the zygomatico-facial canal, from which comes out through the corresponding foramen. It is distributed 1 the skin over the zygomatic bone.

Ophthalmic Artery.—This vessel arises from the internal carotid tery on the inner aspect of the anterior clinoid process, and enters e orbit through the optic foramen, lying beneath the optic nerve, ithin the orbit it is situated for a short distance on the outer side the optic nerve, and then it passes obliquely inwards and forwards a tortuous manner over the nerve to the inner wall of the orbit, len it passes forwards to the region of the medial angular process the frontal bone, near which it divides into its three terminal branches dorsal nasal, supratrochlear, and palpebral.





I26o


A MANUAL OF ANATOMY


Branches. —These are as follows:


1. Central artery of the retina.

2. Posterior ciliary.

3. Lacrimal.

4. Muscular.

5. Supra-orbital.


6. Posterior ethmoidal.

7. Anterior ethmoidal.

8. Palpebral (two), g. Nasal.

10. Frontal.


The central artery of the retina (arteria centralis retinae) aris from the ophthalmic at the back part of the orbit below the opt nerve. Its direction is forwards beneath the nerve, and at a poii about \ inch behind the eyeball it enters the nerve, and passes forwan in its centre to the retina, upon which it ramifies. It must be unde stood that this is the only blood-supply of the retina, and that i obliteration means blindness of the eye to which it goes; it is therefor in spite of its small size, one of the most important arteries in the bod;

The posterior ciliary arteries arise from the ophthalmic whilst is below the optic nerve. They are arranged in two sets, lateral an medial, which pass forwards on either side of the optic nerve to the bac part of the eyeball. Here they pierce the sclera, and the majorit of them enter the choroid coat under the name of the short postern ciliary arteries. Two of them, however, are fairly large, and are know as the long posterior ciliary arteries. They pass forwards betwee the sclera and the choroid, one on each side, and are distributed 1 the ciliary muscle and iris.

The lacrimal artery arises from the ophthalmic on the outer sic of the optic nerve, and passes forwards along the upper border of tl rectus lateralis muscle to the lacrimal gland. In its course it furnish* the following branches: (1) a recurrent meningeal branch, whic passes through the outer part of the superior orbital fissure to tl middle cranial fossa, where it anastomoses with the middle meninge; artery; (2) muscular and anterior ciliary branches, the latter piercir the sclera very near the corneal margin; (3) zygomatic offsets, whic pass through the zygomatico-temporal and zygomatico-facial canals ( the zygomatic bone to the face and temporal region in company wit the respective branches of the temporo-zygomatic nerve; (4) tw lateral palpebral arteries, superior and inferior, which pass inwarc in the upper and lower eyelids, and anastomose with the medi; palpebral branches of the ophthalmic, thus forming arterial arches and (5) glandular branches to the lacrimal gland.

The muscular branches arise from the ophthalmic in two set: outer and inner, and also from some of its branches— e.g., the lacrime and supra-orbital. They furnish a few of the anterior ciliary arteries

The supra-orbital artery arises from the ophthalmic as it crossc inwards over the optic nerve. It courses forwards to the supra orbital notch, through which it passes, with the corresponding nerv* to the forehead. It supplies the upper eyelid and the frontal regior and anastomoses with the superficial temporal and supratrochlea arteries.


THE HEAD AND NECK


1261


Ihe posterior ethmoidal artery, a small vessel, passes through the jsterior ethmoidal canal on the inner wall of the orbit, and is distributed the mucous membrane of the posterior ethmoidal sinus and the ucous membrane of the upper and back part of the outer wall of e nasal cavity. The latter branches pass through foramina in the ibriform plate.

The anterior ethmoidal artery is larger than the preceding. It isses through the anterior ethmoidal canal with the naso-ciliary

rve, and enters the anterior fossa of the base of the skull. Here

crosses the cribriform plate of the ethmoid bone to the nasal slit T the side of the crista galli. It then descends through this slit, rverses the nasal groove on the posterior surface of the nasal bone, id finally passes between the lower border of the nasal bone and the >per nasal cartilage to the tip of the nose. Its branches supply the ira mater in the anterior cranial fossa, the mucous membrane of e anterior ethmoidal sinus and corresponding frontal sinus, the mucous smbrane of the upper and Lcsxl wing of Sphenoid

.tenor parts of the nasal T . , . T ;

isa, and the skin of the tip Frontal Nerve o P uc

the nose. Nerve

The medial palpebral ar- Upper Division of Oculo-motor Nerve_

ies are superior and in- Lower Division /

'ior, and are distributed Abdueent Nerve -.ym /

. .. A . Ophthalmic Vein V/

the eyelids, they arise, _ T _

^ • • A r Fig. 764.—Diagram of the Left Superior

a ^jy °, r c ? n J om t^y» ^ rom Orbital Fissure, showing the Trans e ophthalmic close to the mitted Structures (Posterior View).

Hey of the obliquus su rior muscle, and each takes an outward course in the corresponding elid. They anastomose with the two lateral palpebral branches of e lacrimal artery, thus forming arterial arches.

The dorsal nasal artery leaves the orbit above the medial palpebral

ament, and is distributed to the upper part of the side of the nose

the region of the root, where it anastomoses with the angular and teral nasal branches of the facial artery.

The supratrochlear artery (frontal artery) is the third terminal anch of the ophthalmic. It leaves the orbit at the inner angle, d then ascends to the frontal region, along with the supratrochlear rve, to be distributed to the integument by the side of the median ie. It anastomoses with the supra-orbital artery and its fellow the opposite side. The above description is fairly typical, but the 3 de of origin of the orbital arteries is very variable and, as in most rts of the body, the normal is seldom seen.

Ophthalmic Veins.—These are superior and inferior. The superior hthalmic vein, of large size, begins at the inner angle of the orbit, iere it communicates freely with the facial through the angular in. It accompanies the ophthalmic artery, passing outwards and ckwards over the optic nerve. Having reached the inner end of the perior orbital fissure, the vessel passes between the two heads of the




1262


A MANUAL OF ANATOMY


rectus lateralis muscle, and through the fissure, after which it ope: into the anterior part of the cavernous sinus. Its tributaries corr spond for the most part to the branches of the ophthalmic arter It does not, however, receive the supratrochlear nor the supra-orbit vein. The inferior ophthalmic vein arises in connection with t] lower posterior ciliary and lower muscular veins. It passes backwar along the floor of the orbit, and may join the superior ophthalmic vei open independently into the cavernous sinus, or pass through t] inferior orbital fissure into the pterygoid plexus, with which in ai case it freely communicates.

Structures passing through the Superior Orbital Fissure (Sphenoid Fissure). —These structures are as follows:


1. The oculo-motor nerve.

2. The trochlear nerve.

3. The naso-ciliary, lacrimal,

and frontal nerves.

4. The abducent nerve.

5. The sympathetic root of the

ciliary ganglion.


6. The ophthalmic veins.

7. The orbital branch of t]

middle meningeal artery

8. The recurrent branch of t]

lacrimal artery.

9. The dura mater.


The lacrimal, frontal, and trochlear nerves enter the orbit abo 1 the rectus lateralis muscle, in the order named from without inwards The oculo-motor nerve, the naso-ciliary nerve, and the abduce nerve enter the orbit between the two heads of the rectus lateral muscle, the oculo-motor nerve having already broken up into t\ divisions; and the ophthalmic veins leave the orbit between the t\ heads of the rectus lateralis. The order of parts between the two hea of the rectus lateralis, from above downwards, is as follows:


1. The superior division of the oculo-motor nerve.

2. The naso-ciliary nerve.

3. The inferior division of the oculo-motor nerve.

4. The abducent nerve.

5. The ophthalmic veins (or vein).


The sympathetic root of the ciliary ganglion passes through t superior orbital fissure independently, or along with the naso-cilia nerve, or sometimes with the oculo-motor nerve.

Structures passing through the Inferior Orbital Fissure (Spher maxillary Fissure):

1. Infra-orbital vessels.

2. Infra-orbital nerve.

3. Zygomatic nerve.

4. Inferior ophthalmic vein.

5. Orbital branches of the spheno-palatine ganglion.

6. Lymphatics.


The opening is bridged over by fascia in which involuntary mus: fibres, representing Muller’s muscle of the lower animals, are found. i



THE HEAD AND NECK


1263


THE FACE.

Landmarks.—The glabella can be seen between the eyebrows, and [tending outwards from it on either side is the superciliary arch, ihind the inner part of which is the corresponding frontal sinus! elow the superciliary arch the supra-orbital margin can readily be It, and at the junction of its inner third and outer two-thirds is the [pra-orbital notch, or foramen for the passage of the supra-orbital irve and artery. A line drawn from the position of the suprabital notch to the base of the mandible in such a manner as to pass itween the lower premolar teeth, or, which comes to the same thing, 1 the angle of the mouth, crosses in succession the infra-orbital and ental foramina. The infra-orbital foramen lies in this line at a point )out l inch below the infra-orbital margin, and it indicates the exit the infra-orbital nerve and artery from the infra-orbital canal. The ental foramen in the adult lies midway between the alveolar and Lsilar borders of the mandible, and locates the exit of the mental irve and artery from the mandibular canal.

In line with the tragus of the auricle the zygomatic arch can be It, and leading backwards from it above the orifice of the external iditory meatus is the posterior root of the zygoma. This root is >ntinued into the supramastoid crest, which corresponds to the level the tegmen tympani. Below the supramastoid crest, and just above id behind the external auditory meatus, is the suprameatal triangle, bis triangle lies superficial to the tympanic antrum, and is a most lportant surgical landmark.

The superficial temporal artery and auriculo-temporal nerve lie rectly in front of the tragus, the division of the artery into its anterior id posterior branches taking place about the level of the upper part the auricle. The anterior branch of the artery lies nearly an inch diind the zygomatic process of the frontal bone, and the posterior

  • anch about an inch above the upper part of the auricle.

The parotid gland is situated in front of the auricle. It is limited )ove by the zygoma, behind by the auricle, and interiorly it extends r a limited distance into the digastric triangle of the neck. Anteriorly extends for a short distance superficial to the masseter muscle, and ie parotid duct issues from its anterior border. The course of this ict may be indicated by a line drawn from the intertragic notch to a )int midway between the nostril and the red margin of the upper lip. bout the middle third of this line corresponds to the duct. Above is the transverse facial artery, and below it are the infra-orbital ranches of the facial nerve.

The posterior border of the ramus of the mandible is easily felt, leads superiorly to the condyloid process and mandibular joint, id interiorly to the angle of the bone. Extending forwards from e angle is the base of mandible, which, about an inch from the angle, is a groove for the facial artery, pulsation being readily felt during e in this part of the vessel in front of the masseter muscle, the


1264


A MANUAL OF ANATOMY


anterior vein intervening between the two. In this situation lymphatic gland lies in contact with the artery. From this po the facial artery extends in a tortuous manner to the medial an of the eye, passing close to the angle of the mouth, the anterior fac vein pursuing a comparatively straight course.

Near the mid-line of the face the structures to be noted are ' nasal bones, nasal cartilages, dorsum and apex of the nose, alae n; columna, and the philtrum, which latter is the median groove lead from the columna to the upper lip.

For the component parts of the auricle, see p. 1294.

The eyelids or palpebrae are to be noted, along with the palpeb fissure between them, and the medial and lateral angles at eitl extremity. The tarsus of the upper eyelid can be demonstrated everting the eyelid, and connected with its inner extremity is 1 medial palpebral ligament. This latter may be made tense by draw: the eyelids outwards. It crosses the lacrimal sac a little above 1 centre. The eyelids being everted, the outlines of the tarsal glai may be seen as yellowish streaks perpendicular to the palpeb margins. Behind the eyelashes, or cilia, on the margins of the eyel are the minute orifices of the ducts of the tarsal glands, which ; arranged in a row. Along the line of the eyelashes the skin of i eyelid becomes continuous with the conjunctiva, and along the line reflection of the conjunctiva on to the eyeball the recess, known the fornix, is to be noted. At the medial angle, where the eyelids not meet, there is a recess, known as the lacus lacrimalis, between 1 lids and the eyeball, which lodges a small red fleshy protuberan called the caruncula lacrimalis, provided with a few delicate hai Lateral to this is the fold called the plica semilunaris, which is a vest: of the nictitating membrane or third eyelid of birds. Upon t eyelids at their inner ends the lacrimal papillae are visible, and each papilla is a minute orifice, called the punctum lacrimale. T lower papilla is larger than the upper, and is placed a little farther 0 Each punctum leads into a lacrimal canaliculus, and by these can the tears are conveyed into the lacrimal sac, and thence by the na: lacrimal duct into the inferior meatus of the nose. The position the lacrimal sac may be indicated by drawing the eyelids outwan so as to render tense the medial palpebral ligament, which, as stafi crosses the sac a little above its centre.

Muscles of the Face.

Orbicularis Oculi (Orbicularis Palpebrarum)—Orbital Portion

Origin .—The outer surface of the frontal process of the maxilla, a the medial angular process of the frontal bone.

Insertion .—It is usually said that the orbicular fibres form compl< circles, but it is almost certain that they are serially inserted into t skin, and their place taken by fresh fibres rising from the skin. It only necessary to watch the puckering of the skin on the outer si


THE HEAD AND NECK


1265

ie orbit, where the ' crow’s feet ’ are formed, or the wince of pain w the lower eyelid, to be convinced that there are distinct insertions bres into the skin in these parts.

Palpebral Portion— Origin. —The upper and lower surfaces of the iial palpebral ligament.

Insertion. — 1 he upper and lower surfaces of the lateral palpebral re.

\erve-supply. —Temporal and zygomatic branches of the facial re, in which there may be fibres derived from the nucleus of the o-motor nerve.

Action —Orbital Portion.—(1) The upper half depresses the eyev, and antagonizes the frontal belly of the occipito-frontalis muscle; the lower half elevates the skin of the infra-orbital region. PalpePortion.—This closes the eyelids, as in winking, the upper lid tg depressed and the lower raised, the former movement being e free than the latter. By means of its connection with the medial >ebral ligament the palpebral portion draws forwards the front

of the lacrimal sac, and so contributes to the removal of the tears,

en the entire muscle contracts, the lids are forcibly closed and vn slightly inwards.

rhe upper part of the muscle is related by its deep surface to the dal belly of the occipito-frontalis, the supra-orbital vessels and re, and the supratrochlear nerve, the chief deep relations of the ix part of the levator labii superioris, and, beneath that, the infratal nerve.

Medial Palpebral Ligament (Internal Tarsal Ligament or Tendoli).—It is attached medially to the outer surface of the frontal

ess of the maxilla immediately in front of the naso-lacrimal groove,

direction is outwards in front of the lacrimal sac, and it bifurcates

he medial angle, the divisions diverging, and being attached to

inner extremities of the corresponding tarsus. As the ligament >es just in front of the lacrimal sac it gives origin to the palpebral don of the orbicularis oculi, which explains the action of that don of the muscle upon the sac.

Lateral Palpebral Raph6 (External Tarsal Ligament).—This is tched laterally to the frontal process of the zygomatic bone. Its ction is inwards, and it bifurcates at the lateral angle of the eye the outer extremities of the tarsi.

Lacrimal Portion of Orbicularis Oculi (Tensor Tarsi or Muscle of ner)— Origin. —The crest of the lacrimal bone behind the lacrimal

Insertion .—By means of two slips into the inner extremities of the i of the eyelids, where the fibres become continuous with the ciliary ss of the orbicularis oculi.

Nerve-supply. —As for the rest of orbicularis oculi.

The direction of the muscle is outwards and forwards, and its two s pass behind the lacrimal canaliculi.

Action. —To draw backwards the outer part of the medial palpebral

80



1266


A MANUAL OF ANATOMY


ligament, and in this manner compress the lacrimal sac, the effec which is to force the tears into the naso-lacrimal duct.

Corrugator Supercilii— Origin .—The inner extremity of the su ciliary arch of the frontal bone.

Insertion .—The deep surface of the skin of the eyebrow at centre.

Nerve-supply .—Temporal branches of the facial nerve.


Auricularis Superior


Auricularis Anterior


Auricularis Posterior*


Occipital Belly of -y Occipito-frontalis


Branches from Third and Fourth Cervical Nerves to Trapezius

Scalenus Medius


Lateral Supraclavicular Nerve


Trapezius


"‘Frontal Belly of Occipito frontalis


Orbicularis Oculi


Greater Occipital Nerve Semispinalis Capitis'"' Lesser Occipital Nerve""

Splenius Capitis


Levator Labii Superioris Alaeque N

Levator Labii Super Zygomaticus Minor "Zygomaticus Major “•Masseter


‘“'Orbicularis Oris Depressor Labii Infer! Depressor Anguli Oris Mentalis


Levator Scapulas — Great Auricular Nerve — Accessory Nerve

    • Anterior Belly of Digast

Stemo-hyoid

Mfr SnpeTi ° r Omo-hyoid


- Sterno-mastoid . Anterior Cutaneous Nerve of N


— Medial Supraclavicular Nerve Intermediate Supraclavicular N


Scalenus Anterior

/

Inferior Belly of Omo-hyoid Subclavian Artery (third part)

Fig. 765. —The Right Side of the Head and Neck. The platysma has been removed, and the nerves are shown.


The direction of the muscle is outwards and upwards, and to re the skin the fibres pass through the upper part of the orbicularis 0 and the adjacent portion of the frontal belly of occipito-frontalis.

Action .—To draw the skin of the eyebrow inwards and do wards, giving rise to vertical wrinkles between the eyebrows, a: frowning.

The muscle is under cover of the inner portion of the upper ]











THE HEAD AND NECK 1267

the orbicularis oculi, and it conceals the supratrochlear nerve as merges from the orbit.

Muscles of the Nose—Procerus (Pyramidalis Nasi)— Origin .—The neurosis of the compressor naris over the lower part of the nasal ie.

Insertion. —The deep surface of the skin over the glabella of the ital bone. Some of the fibres become continuous with the medial tion of the frontal belly of occipito-frontalis.

Nerve-supply .—Upper buccal branches of the facial nerve.

Action .—To draw downwards the skin between the eyebrows, ng rise to transverse wrinkles.


Fig. 766. —Dissection of Muscles of Face.

Compressor Naris— Origin .—The maxilla between the canine fossa the nasal notch.

Insertion .—By means of an expanded aponeurosis which blends h its fellow of the opposite side over the cartilaginous portion of nose, and gives origin superiorly to the procerus.

A J erve-snpply .—Upper buccal branches of the facial nerve.

Action .—To depress the cartilaginous portion of the nose.

The muscle is triangular, and at its origin is under cover of the dor labii superioris alaeque nasi.

Levator Labii Superioris Alaeque Nasi— Origin .—The outer surface he frontal process of the maxilla by a pointed extremity. insertion .—By means of two slips. The medial or nasal slip is







1268


A MANUAL OF ANATOMY


inserted into the skin of the ala of the nose, and is often absent. 1 lateral or labial slip is inserted into the skin of the upper lip, some its fibres blending with the levator labii superioris, and others w the upper part of the orbicularis oris.

Nerve-supply .—Buccal branches of the facial nerve.

Action. —(i) To raise the upper lip, and (2) to raise and dilate nostril.

The muscle is triangular, and covers the origin of the compres naris.

Depressor Alse Nasi or Depressor Septi— Origin .—The incisive fo: of the maxilla.

Insertion .—The posterior part of the ala, and the adjacent part the septum of the nose.

N erve-supply .—Upper buccal branches of the facial nerve.

Action .—To depress the ala of the nose.

Dilator Naris Anterior— Origin .—The cartilage of the aperture the nose.

Insertion .—The deep surface of the skin over the ala of the nose

Nerve-supply .—Upper buccal branches of the facial nerve.

Action .—To dilate the nostril.

Dilator Naris Posterior— Origin. —(1) The margin of the na notch of the maxilla; and (2) the accessory cartilages of the nose.

Insertion .—The skin over the back part of the ala of the nose.

Nerve-supply .■—Upper buccal branches of the facial nerve.

Action .—To dilate the nostril.

Levator Labii Superioris— Origin .—The maxilla between the inf orbital foramen and the lower margin of the orbit.

Insertion .—The skin of the upper lip.

Nerve-supply .—Buccal branches of the facial nerve.

Action .—To raise the upper lip.

The muscle is quadrilateral. At its origin it is overlapped by 1 lower half of the orbicularis oculi, and it covers the infra-orbital nei and artery as they leave the infra-orbital foramen. At its insert] the fibres interlace with those of the upper half of the orbicularis ori

Levator Anguli Oris— Origin .—The upper part of the canine fo; of the maxilla under cover of the levator labii superioris.

Insertion .—The angle of the mouth, where some of the fibres < inserted into the skin, whilst others decussate with those of the < pressor anguli oris, and enter the lower lip, mingling with those of 1 lower half of the orbicularis oris.

Nerve-supply .—Buccal branches of the facial nerve.

The direction of the muscle is downwards and slightly outwards

Action .—To raise the angle of the mouth, and at the same time draw it slightly inwards.

The infra-orbital nerve and artery are superficial to the muscle.

Zygomaticus Minor— Origin .—The anterior and lower part of t zygomatic bone close to the maxilla.

Insertion .—The skin of the upper lip immediately lateral to t


THE HEAD AND NECK I2 6 9

itor labii superioris, with the outer border of which muscle some ts fibres blend.

Nerve-supply . Buccal branches of the facial nerve.

The muscle is directed downwards and inwards, and is often irded as part of the orbicularis oculi.

Action.— -To raise feebly the upper lip, and at the same time to w it slightly outwards.

Zygomaticus Major— Origin.— The outer surface of the zygomatic e near the zygomatico-maxillary suture.

Insertion.—The skin at the angle of the mouth, where its fibres id with those of the orbicularis oris.

Nerve-supply. —Buccal branches of the facial nerve.

The muscle is directed downwards and inwards.

Action.— To draw the angle of the mouth upwards and outwards.


Buccal Nerve (cut)


i

Upper Head of Lateral Pterygoid

i


Capsule of Mandibular '^ Joint


Lower Head of Lateral Pterygoid

Pterygo-mandibular

Ligament

  • Parotid Duct


X Buccinator


Medial Pterygoid


Fig. 767. —The Pterygoid and Buccinator Muscles.


Risorius— Origin. — The deep fascia which covers the masseter scle and parotid gland.

Insertion. The skin at the angle of the mouth, where its fibres id with the orbicularis oris.

Nerve-supply. —Buccal branches of the facial nerve.

The direction of the muscle is inwards, some of its fasciculi also ending.

Action. —To draw the angle of the mouth outwards and slightly mwards. It is often the first muscle affected in tetanus, and gives to the ‘ risus sardonicus/

The muscle consists of a few scattered fasciculi, which are emded in the adipose tissue over the buccinator; it is a detached tion of the platysma.

Buccinator— Origin. — (1) The outer surfaces of the alveolar pro




1270


A MANUAL OF ANATOMY


cesses of the maxilla and mandible, opposite the three molar socl and (2) the anterior aspect of the pterygo-mandibular ligament.

Insertion. —The orbicularis oris at the angle of the mouth.

The central fibres decussate, those from above entering the lc lip, and those from below entering the upper lip. The highest lowest fibres take no part in this decussation, the highest pas directly into the upper lip, and the lowest into the lower lip Fig. 768).

N erve-supply. —Lower buccal branches of the facial nerve.

Action. —To draw the angle of the mouth outwards, and p the lips and cheeks against the teeth, thus preventing the food f accumulating between the lips and the teeth during masticat and to contract the vestibular part of the mouth spasmodically, a whistling.

The muscle is expanded over the cheek, but towards the angl the mouth it becomes narrow and thick. It is pierced by the par duct opposite the second upper molar tooth, and the buccal n( also passes through it on its way to the mucous membrane of cheek. Externally the muscle is overlapped by the anterior bo] of the masseter, from which it is separated by the suctorial of fat.

Suctorial Pad of Fat (Buccal Pad). —This is a well-defined colleci of fat which is situated upon the buccinator muscle close to the ante border of the masseter. Well developed in healthy young adults may be absorbed or replaced very quickly, causing marked chang< the facial expression.

Depressor Anguli Oris (Triangularis Menti)— Origin. —The obli line of the mandible from about the level of the canine socket to t of the first molar.

Insertion. —The angle of the mouth, where some of the fibres attached to the skin, whilst others decussate with those of the leva anguli oris and enter the upper lip, in which they mingle with upper part of the orbicularis oris.

N erve-supply. —The mandibular branch of the facial nerve.

Action .—To depress the angle of the mouth.

Depressor Labii Inferioris (Quadratus Menti)— Origin. —The loi part of the outer surface of the body of the mandible close to symphysis, and extending outwards to below the mental foramen.

Insertion .—The skin of the lower lip.

Nerve-supply. —The mandibular branch of the facial nerve.

The muscle is directed upwards and inwards.

Action .—To draw the lower lip downwards and slightly outward

The muscle is overlapped laterally by a portion of the depres anguli oris, and medially it is in contact superiorly with its fellow the opposite side. The deep surface is related laterally to the men foramen and the mental nerve and vessels, and medially to part the mentalis. In the lower lip its fibres pass amongst those of 1 lower part of the orbicularis oris.


THE HEAD AND NECK


1271


Mentalis ^Levator Menti)— Origin. —The incisive fossa of the

mdible.

Insertion. — The skin of the chin.

Nerve-supply. —The mandibular branch of the facial nerve.

The muscle is directed downwards and forwards.

Action. — (1) To raise the integument of the chin, and (2) to elevate

d protrude the lower lip.

Orbicularis Oris. —This is a complex muscle composed of three ‘ata. The superficial stratum consists of fibres which are prolonged >m the elevators and depressors of the angles of the mouth, and tend as far as the centre of the lip, but are not continuous with ose of the opposite half. They are inserted into the skin, and are rtially reinforced by fibres from the elevators of the upper lip, thegomatic muscles, the risorius, the posterior fibres of the platysma, d the depressor labii inferioris.

The intermediate stratum consists of fibres which are derived from e buccinator muscles. These fibres are disposed transversely, ard


Fig. 768. —Plan of Composition of Orbicularis Oris.


ose of opposite sides are directly continuous. The fibres of this ratum extend to the margins of the lips.

The foregoing fibres are destitute of bony and cartilaginous attaches.

The deepest stratum consists of fibres which arise from the incisive sSct of the upper and lower jaws, as well as from each side of the

terior nasal spine.

Nerve-supply. —The low*er buccal and mandibular branches of the

dal nerve.

Action .— 1 To close the oral aperture; and [2) to press the lips ainst the alveolar margins.

The muscle is separated from the buccal mucous membrane by the Mai arteries and the labial mucous glands.

The labial mucous glands, which are racemose, or acino-tubular, e numerous, and each is about the size of a small pea. They are uated on the deep surface of the mucous membrane of the lips, lere thev lie in the loose areolar tissue between the mucous memane and the orbicularis oris. Their ducts open into the vestibule the mouth.







I2J2


A MANUAL OF ANATOMY


The buccal mucous glands, also racemose, or acino-tubular, situated between the mucous membrane of the cheek and the d surface of the buccinator.

The molar mucous glands, also racemose, or acino-tubular, superficial to the buccinator in the vicinity of the terminal pari the parotid duct. They are four or five in number, and their du having pierced the buccinator, open into the vestibule of the mo opposite the molar teeth.


Nerves of the Face.

The nerves of the face are thirteen in number on either si Twelve of these are sensory nerves, and one is motor—namely, facial nerve.

The facial or seventh cranial nerve will only be described b after its emergence from the facial canal in the petrous part of temporal bone. It comes out of that canal through the stylo-mast foramen, after which it passes downwards and then forwards into parotid gland. Near the posterior border of the ramus of the mandi it breaks up into two terminal parts, called the temporo-facial c cervico-facial divisions.

Branches. —The posterior auricular, digastric, stylo-hyoid, c the terminal divisions.

The posterior auricular nerve arises from the facial close to stylo-mastoid foramen. It ascends between the auricle and mastoid process, where it lies deeply, and divides into two branch auricular and occipital. The auricular branch passes upwards beh: the auricle and deep to the auricularis posterior, to be distributed that muscle, and it may be to the auricularis superior, as well as the small intrinsic muscles on the inner aspect of the auricle. 1 occipital branch passes backwards to supply the occipital belly of i occipito-frontalis muscle. The posterior auricular nerve communica with the great auricular, the lesser occipital, and the auricular brar of the vagus.

The digastric branch is directed downwards to the posterior be of the digastric muscle. One of the digastric branches communica with the glosso-pharyngeal nerve.

The stylo-hyoid branch usually arises in common with the p ceding. It is of some length, and, passing forwards, it enters the sty hyoid muscle about its centre.

The terminal branches continue to pass forwards in the paro gland, crossing superficially the posterior facial vein and the exteri carotid artery, the direction of these vessels being vertical. In t part of their course these branches receive the following communi< tions: two branches from the auriculo-temporal nerve, and brand from the great auricular nerve. Each terminal branch breaks, within the gland into smaller branches, and as these pass in varic directions over the face and upper portion of the neck they ram


THE HEAD AND NECK


1273


3ely. The latter branches frequently communicate with each other a plexiform manner, both in the parotid gland and on the face, the exus thus formed being known as the parotid plexus (pes anserinus). le ramifications also communicate with the branches of the three visions of the trigeminal nerve which appear on the face, these being nsory nerves.

The terminal branches of the facial nerve are; The temporal branches cend over the zygomatic arch to the temporal region, and are dis

Upper Terminal Division of Facial Nerve

Temporal Branches of Facial Nerve


Zygomatic Branches of Facial Nerve


llo-temporal Nerve

5 rior Auricular Nerve

ater Occipital Nerve

acial Nerve at Stylomastoid Foramen

Digastric Branch of Facial Nerve

er Terminal Division of Facial Nerve


Branch of Lacrimal Nerve


Supra-orbital Nerve (in two divisions)

.. Infratrochlear Nerve


Zygomatico-facial

Nerve

Ext. Nasal N. Infra-orbital N.

Upper Buccal Branches of Facial Nerve

-Buccal Nerve


.. Mental Nerve


Lesser Occipital Nerve

Great Auricular Nerve Anterior Cutaneous Nerve of Neck


Parotid Gland

' Lower Buccal Branches of Facial N.

\

'Mandibular Branches of Facial Nerve Cervical Branches of Facial Nerve


External Jugular Vein


ig. 769. —Superficial Dissection of the Right Side of the Head and Upper Part of the Neck (Hirschfeld and Leveille).

1, sterno-mastoid; 2, trapezius.


ibuted to the auriculares anterior et superior, the intrinsic muscles 1 the outer surface of the auricle, the frontal belly of the occipito^ntalis, the upper part of the orbicularis oculi, and the corrugator percilii. These branches communicate with the supra-orbital and -rimal branches of the ophthalmic, the zygomatico-temporal nerve =>m the maxillary, and the auriculo-temporal of the mandibular, l of these being sensory nerves.

The zygomatic branches pass forwards over the zygomatic bone wards the outer angle of the orbit, and supply the outer part of the

















I2 74


A MANUAL OF ANATOMY


orbicularis oculi. They form communications with the lacrimal bran of the ophthalmic and with the zygomatico-facial nerve.

The upper buccal branches pass forwards to the region betwe the lower margin of the orbit and the upper lip. They supply t lower part of the orbicularis oculi, the muscles of the nose, the elevah of the upper lip, and the upper part of the orbicularis oris. Th communicate with the following sensory nerves: the infra-orbital the maxillary, the infratrochlear of the naso-ciliary, and the exteri nasal branch of the naso-ciliary from the ophthalmic. The commu:


C.A. Communicating Twigs with Auditory G.G. Facial Ganglion G.S.P. Greater Superficial Petrosal S.S.P. Branch to Lesser Superficial Petrosal E.S.P. External Petrosal

S. Branch to Stapedius Muscle C.T. Chorda Tympani A Auricular Branch S.M.F. Stylo-mastoid Foramen P.A. Posterior Auricular S.H. Branch to Stylo-hyoid Muscle

D. Branch to Posterior Belly of Digastric


A.T. Communicating Branches from Auriculotemporal

T.F. Upper Terminal Division T. Temporal Branches M. Zygomatic Branches I.O. Upper Buccal Branches G.A. Communicating Branches from Great Auricular

C.F. Lower Terminal Division B. Lower Buccal Branches S.M. Mandibular Branches I.M. Cervical Branches


cations with the infra-orbital nerve take place under cover of t levator labii superioris muscle, and form a somewhat intricate plexi called the infra-orbital plexus.

The lower buccal branches pass forwards over part of the massei and the buccinator muscles to the angle of the mouth. They supply t buccinator and the outer part of the orbicularis oris, and are connect with the infra-orbital branches of the temporo-facial division, and wi the buccal nerve , which is a branch of the mandibular division of t trigeminal nerve. The latter communications take the form of a plex












THE HEAD AND NECK


1275


ituated on the superficial surface of the buccinator muscle, called the uccal plexus.

The mandibular branches pass forwards over the mandible to the sgion below the lower lip. They supply the lower part of the orbicuiris oris, depressor anguli oris, depressor, labii inferioris and mental luscles. They communicate with the mental branch of the inferior ental from the mandibular nerve under cover of the depressor anguli ris.

The cervical branch descends beneath the upper part of the platysma nd the deep cervical fascia to the suprahyoid region. Having pierced tie deep fascia, it divides into branches which curve forwards and upply the platysma on its deep surface. It communicates freely


Fig. 771.— Diagram of the Sensory Nerves of the Right Side of

the Head.


1. Supra-orbital

2. Supratrochlear

3. Infratrochlear

4. External Nasal

5. Lacrimal


6 . Zygomatico-temporal

7. Zygomatico-facial

8. Infra-orbital

9. Auriculo-temporal

10. Buccal


11. Mental

12. Great Auricular

13. Lesser Occipital

14. Greater Occipital


ith the upper branch of the anterior cutaneous nerve of the neck from tie cervical plexus.

Summary of the Facial Nerve. —The facial nerve, after leaving the facial anal through the stylo-mastoid foramen, supplies the following muscles: (1) the xtrinsic and intrinsic muscle of the auricle; (2) the posterior belly of the digastric nd the stylo-hyoid; (3) the occipito-frontalis; (4) the superficial muscles of the ice, including the buccinator, but not the masseter, nor the levator palpebrae aperioris; and (5) the platysma. All these muscles, except the posterior belly f the digastric and the stylo-hyoid, are spoken of as muscles of expression. The erve establishes free communications with all three divisions of the trigeminal erve, which are sensory. It also communicates with the lesser occipital, great uricular, and anterior cutaneous nerve of neck, which are branches of the ervical plexus.

Sensory Nerves of the Face. —These, with one exception, are deived from the trigeminal nerve, the exception being the great auricular, duch is a branch of the cervical plexus.






1276


A MANUAL OF ANATOMY


A. Branches of the Trigeminal Nerve.


Distal Sources.


Proximate Sources.


t. Ophthalmic nerve.


2. Maxillary nerve.


3. Mandibular nerve.


(a) Frontal

- ( b ) Lacrimal.

(c) Naso-ciliary.

[ (a) Maxillary.

| ( b ) Zygomatic.

f (a) Anterior division.

| ( b) Posterior division.

I ( c ) Inferior dental of I posterior division.


Terminations.

f Supra-orbital.

I Supratrochlear.

Lacrimal, j Infratrochlear.

( External nasal.

Infra-orbital.

/ Zygomatico-temporal. I Zygomatico-facial. Buccal.

Auriculo-temporal. j Mental.


B. Facial Branches of the Great Auricular Nerve.

Branches of the Trigeminal Nerve. —The supra-orbital and supri trochlear nerves have been already described (see p. 1153). T1 former is distributed to the skin of the frontal region and the upp< part of the scalp; and the latter to the skin of the lower and centr; portion of the frontal region. Both these nerves furnish twigs to tt skin of the upper eyelid.

The lacrimal nerve pierces the orbital septum, and is distribute to the skin and conjunctiva of the outer part of the upper eyelid, as we as to the skin in the immediate vicinity of the zygomatic process ( the frontal bone.

The infratrochlear branch of the naso-ciliary nerve leaves the orb below the pulley of the obliquus superior muscle, and furnishes twig to the skin and conjunctiva of the inner parts of the eyelids, the sic of the root of the nose, the lacrimal sac, and the caruncula lacrimalis.

The external nasal branch of the naso-ciliary nerve emerges betwee the lower border of the nasal bone and the upper nasal cartilage, an descends beneath the compressor naris muscle to the apex of the nos< Its twigs supply the skin of the tip and lower part of the side of th nose.

The infra-orbital nerve is the terminal part of the maxillary divisio of the trigeminal. It leaves the infra-orbital canal through the infn orbital foramen, where it is under cover of the levator labii superior! In this situation it communicates with the upper buccal branches ( the facial, forming the infra-orbital plexus, and it divides into three sel of branches—namely, palpebral, nasal, and labial. The palpebra branches ascend to supply the skin and conjunctiva of the lower eyelic The nasal branches pass inwards, and are distributed to the skin of th side of the nose. The labial branches, long and large, descend to suppl the skin and mucous membrane of one half of the upper lip. As the descend they furnish twigs to the skin between the infra-orbital forame and the upper lip.

The zygomatico-temporal nerve (temporo-malar nerve) is of sma

size. Having traversed the zygomatico-tempora] canal in the zygomati


THE HEAD AND NECK


1277

one, it pierces the temporal fascia about 1 inch above the front part f the zygoma, and behind the marginal process on the postero-superior r temporal border of the zygomatic bone, and is distributed to a mited portion of the skin over the anterior part of the temporal 3gion.

The zygomatico-facial nerve (temporo-malar nerve) is of small size, nd emerges from the zygomatico-facial canal in the zygomatic bone tirough the zygomatico-facial foramen. It is distributed to the skin ver the malar bone.


The buccal nerve is a branch of the anterior division of the mandiblar nerve. Coming from under cover of the middle of the anterior order of the masseter on to the superficial surface of the buccinator, divides into branches which communicate freely with the buccal ranches of the facial nerve, forming the buccal plexus. Its final (stribution is to the skin and mucous membrane of the cheek, the ranches to the latter piercing the buccinator.

The auriculo-temporal nerve, which is a branch of the posterior ivision of the mandibular nerve, has been already described as ! gards its cutaneous distribution (see p. 1157).

The mental nerve is one of the terminal branches of the inferior 5ntal, which in turn is a branch of the posterior division of the






A MANUAL OF ANATOMY


1278

mandibular nerve. Leaving the mental foramen under cover of t depressor anguli oris, and in line with the interval between the t\ lower premolar sockets, its branches supply the skin and muco membrane of one half of the lower lip, and the skin covering the bo< of the mandible.

The supra-orbital, infra-orbital, and mental nerves being frequent the seat of neuralgia, their positions for purposes of operative tre; ment can readily be ascertained in the following manner: A line dra\ upwards from the position of the mental foramen, which is in line wi the interval between the two lower premolar sockets, to the supr orbital notch, which is situated at the junction of the outer two-thir and the inner third of the supra-orbital arch, will cross the infra-orbil foramen. This line, therefore, is over the points of emergence of the three important sensory nerves.

From a clinical point of view it is sometimes more important recognize the areas supplied by the three divisions of the trigemir nerve than to identify the distribution of each particular branc These areas are shown in Fig. 772. It must be clearly understoc however, that here, as in all other parts of the surface of the bod one nerve area overlaps another very greatly.

Branches of the Great Auricular Nerve.—The facial branches the great auricular nerve, which is a branch of the cervical plexi are distributed to the skin over the parotid gland. They send twi into the gland which communicate with the branches of the fac: nerve.


Arteries of the Face.

The arteries of the face are as follows:


Sources.

External

carotid.

Ophthalmic,

from

internal

carotid.

Lacrimal,

from

ophthalmic.


Arteries.

| Facial.

'Dorsal nasal.

Supra-trochlear.

Supra-orbital.

Medial palpebral

(superior and inferior). f Lateral palpebral

(superior and inferior). [ Zygomatic.


Sources.

Superficial

temporal.

Maxillary.

Inferior dental, from

maxillary.


Arteries.

(Transverse facial.

■j Anterior temporal ’ Zygomatic. Infra-orbital.«  Buccal. ~

l Mental.

)


The chief of these arteries are the facial and the transverse faci;

Facial Artery.—The facial artery (external maxillary ) is the highe of the three anterior branches of the external carotid. It is situat at first in the upper portion of the anterior triangle of the neck, whe it has been previously described (see p. 1217). It leaves the neck ai enters upon its facial course by mounting over the body of d mandible in front of the anterior border of the masseter, where it very superficial, being covered only by the platysma and the integ ment. From this point it has a very tortuous course to the angle



THE HEAD AND NECK


1279


e mouth, the angle of the nose, and the inner angle of the eye, though may end at either of the two former points. The facial part of the

ssel is never very deepfy placed.

Relations— Siiperficial. —The skin and platysma, the risorius, the gomatic muscles, and branches of the facial nerve. It may be deep superficial to the levator labii superioris; where it crosses the body the mandible the anterior facial vein is often superficial to it. Deep. The body of the mandible (where pulsation can readily be felt in the

ssel), the buccinator, the levator anguli oris, and the infra-orbital
rve.


Fig. 773. —The Arteries of the Right Side of the Head (after

L. Testut’s ‘ Anatomie Humaine ’).


Facial Branches.—-(1) Muscular branches, of small size, arise from e outer side of the vessel, and are distributed to the structures in the asseteric, buccal, and infra-orbital regions, where they anastomose ith the buccal, transverse facial, and infra-orbital arteries. (2) The ental branch [inferior labial artery of the O.T.) passes forwards over e body of the mandible, and deep to the depressor anguli oris, to pply the structures between the lower lip and the base of the mandible, anastomoses with the inferior labial, mental, and submental arteries. ) The inferior labial a,rtery (inferior coronary artery ) arises just below e angle of the mouth, and passes inwards deep to the depressor iguli oris. In the lower lip it lies near the margin, between the bicularis oris and the mucous membrane, and anastomoses with its How of the opposite side, and with the previous branch. (4) The




I28o


A MANUAL OF ANATOMY


superior labial artery (superior coronary artery ), of larger size than 1 inferior, arises just above the angle of the mouth under cover of 1 zygomaticus major. Its position in the upper lip is similar to that the inferior labial in the lower lip, and it anastomoses with its fell of the opposite side. Near the middle line it furnishes the sefi branch , which ramifies on the columna as far as the tip of the no The superior and inferior labial arteries of each side sometimes ar together. The vessels of each side, superior and inferior, form in ea lip a tortuous arterial arch, which is necessarily divided in operatic upon one or other lip. (5) The lateral nasal branch arises oppos the nose, and lies on the sulcus above' the ala. It anastomoses w: the dorsal nasal branch of the ophthalmicy^the septal branch, t terminal branch of the anterior ethmoidal artery, and its fellow of i opposite side, the facial at the medialNartery of the eye.

lies either deep to, or; embedded in, the levator labii superioris alaeq nasi, and supplies the. side of the root of the nose and the adjacc part of the orbicularis oculi. It anastomoses with the dorsal na branch of the ophthalmic artery. ; x x

The anterior facial vein starts above the medial angle of the e by the union of the supratrochlear and ^upfa-orbital veins. T course of the vessel is a straight one, downwards ancboutwards, late: to the artery, and at a little distance from 1 it, except over the low border of the mandible, where' it lies close to its outer side and contact with the anterior border of the masseter. In its course crosses the end of the parotid duct. The cervical part of the ve which ends in the internal jugular, has been already described. T

muscular relations of the vein are the same as those of the arte]

’ ' ., - ? 1 *

except that it is always superficial to the levator labii superioris.

Its tributaries are: (1) the supratrochlear vein (frontal veil (2) the supra-orbital vein, which communicates with the ophthaln vein; (3) the lateral nasal veins, and laterally a few superior palpeb: veins, whilst posteriorly it communicates with the superior ophthaln vein, and may communicate with its fellow of the opposite side by mea of the transverse nasal vein, which lies over the bridge of the no< (4) a few inferior palpebral veins, which are in communication wi the infra-orbital vein; (5) the superior labial vein, which issues fron plexus in the upper lip (the blood from the similar plexus in the low lip passing to the submental region, where it takes part in the formati of the anterior jugular vein); (6) the deep facial vein, of variable si: which, coming from the pterygoid plexus, appears deep to the anter: border of the ramus of the mandible and of the masseter muscle; a: (7) parotid, masseteric, and buccal branches.

Facial Lymph Glands. — These glands lie on the face along t course of the anterior facial vein. Some are situated upon the mandil deep to the platysma, one of them being placed upon the base of t mandible close to the facial vessels; others ( buccal ) rest upon t fascia, covering the buccinator muscle; and the remaining glar of this group are met with between the angle of the mouth and t


THE HEAD AND NECK 1281

edial angle of the eye. I hey receive their afferent vessels from ie neighbouring structures, and their efferent vessels pass to the ibmandibular lymph glands. ‘

Transverse Facial Artery.— This vessel arises from the superficial mporal in the parotid gland, and passes horizontally forwards, fter leaving the anterior border of the gland it crosses the masseter, iving the zygoma above it and the parotid duct below it, the upper lccal branches of the facial nerve being in turn below the parotid ict. The order of structures from above downwards is, accordingly, tery, duct, and nerves. The artery is distributed to the parotid and, the masseter muscle, and the structures on the side of the

ce, and it anastomoses with the infra-orbital, zygomatic, facial id buccal arteries.

The transverse facial vein joins the superficial temporal vein, ihe dorsal nasal artery is one of the terminal branches of the ihthalmic, and leaves the orbit at the medial angle of the eye above e medial palpebral ligament. It is distributed to the lacrimal sac id the side of the root of the nose, and anastomoses with the terminal anches of the facial artery. Sometimes it gives off a transverse isal branch, which crosses the root of the nose and anastomoses th its fellow of the opposite side.

The supra-orbital and supratrochlear arteries have been already scribed (see p. 1153).

Ihe medial palpebral arteries, superior and inferior, arise from e ophthalmic and leave the orbit at the medial angle, one passing •ove and the other below the medial palpebral ligament. Their urse is outwards between the palpebral fibres of the orbicularis uli and the tarsi of the eyelids, and they anastomose and form arches th the lateral palpebral branches of the lacrimal artery. They e distributed to the palpebral structures, the lacrimal sac, and e caruncula lacrimalis.

The corresponding veins from the upper and lower eyelids open to the commencement of the anterior facial vein.

The terminal branch of the anterior ethmoidal artery emerges, )ng with the terminal branch of the naso-ciliary nerve, between e lower border of the nasal bone and the upper nasal cartilage, is distributed to the skin of the apex and the lower part of the ie of the nose.

The lateral palpebral arteries, superior and inferior, are branches the lacrimal artery within the orbit. Their course is inwards tween the palpebral fibres of the orbicularis oculi and the tarsi the eyelids, and they anastomose and form arches with the palpebral inches of the ophthalmic.

the lateral palpebral veins end in the zygomatic vein, which opens

0 the middle temporal, and this in turn joins the superficial temporal

m.

The zygomatic branches of the lacrimal artery accompany the ^omatico-facial and zygomatico-temporal nerves.


81


1282


A MANUAL OF ANATOMY


The zygomatic artery and anterior branch of the superficial tempo artery have been already described (see p. 1158).

The infra-orbital artery arises from the third part of the maxilh in the pterygo-palatine fossa. Having passed horizontally forwar with the infra-orbital nerve, through the infra-orbital canal, it ri with that nerve through the infra-orbital foramen, lying under co of the levator labii superioris muscle. It then gives branches upwai to the lower eyelids, inwards to the side of the nose, and downwai towards the upper lip. It anastomoses with the palpebral, faci transverse facial, and buccal arteries.


Sometimes, when the facial artery ends at the angle of the mou the infra-orbital is very large, and supplies all the upper part of face, including the nose. This arrangement, common enough pronograde mammals, shows that the infra-orbital, and not superficial temporal, is morphologically the terminal twig m external carotid arterial tree.

The infra-orbital vein, having traversed the infra-orbital car

opens into the pterygoid plexus.

The buccal artery is a branch of the second part of the maxilla It accompanies the buccal nerve to the superficial surface of







THE HEAD AND NECK


1283


ccinator muscle, and is distributed to that muscle and to the mucous ■mbrane of the cheek. It anastomoses with branches of the facial

ery.

The mental branch of the inferior dental from the first part of the ixillary is found with the mental nerve at the mental foramen, lying der cover of the depressor anguli oris muscle. It supplies the uctures here, and anastomoses with the inferior labial and submtal arteries.

The mental vein joins the inferior dental vein, which opens into s pterygoid plexus.

Lymphatics.—The lymphatics of the face are arranged in two

s, superficial and deep. The superficial lymphatics for the most

rt take a course similar to that of the anterior facial vein, and end the submandibular lymph glands. They receive the lymphatics (1) the inner part of the frontal region at the medial angle of the eye; the inner parts of the eyelids; (3) the side of the nose; (4) the part the face between the lower eyelid and upper lip; and (5) sometimes e upper lip. The lymphatics from the temporal and outer part of e frontal regions, from the front of the auricle, from the greater rt of the eyelids, and from the outer part of the cheek end in the perficial parotid lymphatic glands. The deep lymphatics , including ose of the orbit, anterior part of the nasal cavity, roof of the mouth, d temporal and infratemporal fossae, run to the deep facial lymph mds.

Parotid Lymph Glands (Pre-auricular Lymph Glands).—These mds are arranged in two groups —superficial and deep.

The superficial parotid lymph glands lie upon the superficial surface the parotid salivary gland immediately beneath the parotid fascia, d in front of the tragus of the auricle. They receive their afferent ssels from the following sources.

1. The outer surface of the auricle.

2. The anterior wall of the external auditory meatus.

3. The eyebrow, and upper and lower eyelids.

4. The root of the nose.

5. The upper part of the cheek.

Their efferent vessels pass to (1) the upper superficial cervical lymph mds, and (2) the superior deep cervical lymph glands.

The deep parotid lymph glands lie within the parotid salivary gland )ng the terminal part of the external carotid artery. They receive eir afferent vessels from the following sources :

1. The tympanic cavity in part.

2. The frontal region of the scalp.

3. The anterior temporo-parietal region of the scalp.

4. The parotid salivary gland.

5. The deep facial lymph glands.

Their efferent vessels pass to the superior cervical lymph glands.


1284


A MANUAL OF ANATOMY


Buccinator Lymph Glands.—These glands are situated on buccinator muscle. They receive a few afferent lymphatics from zygomatic region and the lateral aspect of the face, but most of t drainage is from the inner side of the cheek, and their efferent lympha pass to the parotid and submandibular lymph glands.

Parotid Gland.—This gland is an inverted pyramid, having 1 sides and a base, and fills the space which is left by the ramus of mandible anteriorly, the sterno-mastoid muscle posteriorly, the sty process medially, and the articular eminence and root of the zyg(


Fig. 775. —The Parotid Gland in Position.

superiorly. Where the anterior border of the sterno-mastoid touc the angle of the mandible the apex is situated. The anterior, poster and medial surfaces are grooved by the structures which bound gland.

The lateral surface is flat, flush with the side of the face, £ overlaps the ramus of the mandible and masseter muscle for a c siderable extent, forming the accessory part, from the anterior bor of which the parotid duct, the transverse facial artery, and the branches of the facial nerve leave the gland.




THE HEAD AND NECK


1285


Embedded in the upper part of the lateral surface are the superficial otid lymph glands already described (p. 1283), while from the surface gs of the great auricular nerve come out to supply the skin covering gland.

The anterior surface is very deeply grooved by the posterior border the ramus of the mandible and of the masseter muscle, the outer of the groove projecting forwards as the accessory part already ken of, while the inner or deep lip pushes its way forwards into triangular space left between the lateral and medial pterygoid scles. It is at the anterior border of the latter part of the gland t the maxillary artery leaves and the maxillary vein enters the


Fig. 776. —Horizontal Section through Parotid Gland and

Neighbouring Structures.


id. The deep Surface is grooved by the styloid process and the scles rising from it, though not very deeply, and the lips of the ove may be conveniently referred to as pre- and post-styloid ridges.

' pre-styloid ridge is in contact with the internal carotid artery, le the post-styloid is, perhaps, the most important and interes ting t of the whole gland, because it touches the internal jugular vein i the accessory and glosso-pharyngeal nerves, which are so closely iciated with that vein, and also because, near its upper end, the facial ve, and near its lower end the external carotid artery enter the id. In addition to these, the posterior auricular artery runs up ier just deep to or embedded in the post-styloid ridge until it lies t behind the point of entry of the facial nerve.





1286


A MANUAL OF ANATOMY


The projection of the post-styloid ridge is evidently due to gland pushing its way in between the styloid process in front and transverse process of the atlas behind, and that part of the deep surf; of the gland which lies behind the post-styloid ridge is close to transverse process and to the muscles rising from it; while, near apex, the posterior facial vein leaves the gland on this aspect.

The posterior surface is usually grooved by the mastoid proc above and the sterno-mastoid muscle lower down, and entering


Fig. 777.—To show Deep Relations of Parotid (Interrupted Line)

lower part of the superficial lip of this groove is the great auricu nerve.

The base of the gland is very deeply notched anteriorly by the ne of the condyloid process, behind which the superficial temporal arte and vein are seen leaving and entering the gland, the vein being sup ficial; in front of them the temporal branch of the facial nerve rr from the gland across the root of the zygoma, while behind them the superficial temporal branch of the auriculo-temporal nerve. T nerve is, as a rule, not really embedded in the gland, but rests for t most part on its base, between the parotid and the skull, as it ru


Orb. Oculi


— Orb. Oris

-Masseter

Buccinator

_—r Mandible

Ext. Carotid

Plat ysma




THE HEAD AND NECK


1287


lcIc from the region of the foramen spinosum, where it embraces the iddle meningeal artery. Having passed back on the deep aspect of e superficial temporal vessels, the nerve gives off its auricular, parotid, id articular branches, and then runs outwards and upwards just Tind the articulation and just in front of a thin, tongue-like process

the gland which moulds itself into the non-articular part of the ticular fossa, behind the squamo-tympanic fissure, and in contact ith the tympanic plate.

Summing up the foregoing, it will be understood that the parotid and forms an accurate cast of the cavities which the surrounding ructures have left for it, pushing its processes and its pre- and postyloid ridges into every available cranny. Doubtless, too, it is able > adapt its shape to these cavities as they change with every moveten t of the jaw.

Several important structures traverse the gland: (1) The external irotid artery ascends deeply in it as high as the level of the neck f the mandible, where it divides into the superficial temporal and laxillary arteries, which are at first embedded in the gland. Whilst 1 the gland the superficial temporal artery gives off its transverse facial nd auricular branches. (2) The superficial temporal and maxillary eins unite in the gland, at the level of the neck of the mandible, to form tie posterior facial vein, which descends from that level within the land, lying superficial to the external carotid artery, and close to the iwer border of the gland it breaks up into an anterior and a posterior ivision. (3) The external jugular vein is formed near the lower part f the gland by the union of the posterior auricular vein with the osterior division of the posterior facial vein. (4) The facial nerve raverses the gland from behind forwards, and in doing so breaks Lp into its terminal divisions, the branches of which leave the gland nteriorly and superiorly. The nerve is superficial to the external arotid artery and posterior facial vein. (5) Entering the lower part f the gland are branches of the great auricular nerve, which comaunicate within the gland with the facial nerve. (6) The auriculoemporal nerve is related to the upper part of the gland, where it

ives branches to it which communicate with the facial nerve.

Parotid duct, or duct of Stensen, dense and tough, leaves the anterior )order of the gland, and passes forwards on the masseter muscle, ying fully \ inch below the zygomatic arch. In this part of its course t is accompanied for a short distance by the accessory part of the )arotid gland which, with the transverse facial artery, lies above it, vhilst the upper buccal branches of the facial nerve are placed below t. After leaving the surface of the masseter muscle the duct dips leeply through the fat covering the buccinator, and pierces that muscle, [t then passes forwards for a very short distance between the muscle uid tEe buccal mucous membrane, which it finally pierces to end in 1 minute opening on a small papilla situated opposite the crown of he second upper molar tooth. The duct is about the size of a crowpiill, its diameter being about J inch, except at its buccal orifice,


12 88


A MANUAL OF ANATOMY


where it becomes narrow. It is about 2 inches in length, and it course may be indicated by a line drawn from the intertragus note! or from the junction of the lobule and cartilage of the auricle, to point midway between the nostril and the red margin of the uppe lip. About the middle third of this line corresponds to the duct.

Blood-supply. —The arteries are derived from (1) the externa carotid, (2) the superficial temporal, (3) the transverse facial, an* (4) the posterior auricular.

Lymphatics.— These pass to the superficial and deep cervical lympj glands, having previously traversed the parotid lymph glands, and in the case of some, the submandibular glands.

Nerve-supply. —(1) The auriculo-temporal nerve, which conveys t the gland secretory fibres of the glosso-pharyngeal nerve through it


Parotid Duct


tympanic branch, the lesser superficial petrosal nerve, and the oti< ganglion; (2) the great auricular nerve; (3) the sympathetic plexu; on the external carotid artery; and (4) the facial nerve.

Structure. —The parotid gland is a compound racemose or acino-tubular gland and is composed of large lobules, which are united by connective tissue. Eacl of these is made up of smaller lobules, likewise connected by connective tissue Each small lobule is a gland on a minute scale, and is made up of a group of mor< or less sacculated tubules, called alveoli or acini. A duct passes from each smal lobule, which unites with adjacent ducts, and these in turn unite, larger and stil larger ducts being formed, the resultant being the principal duct, called th< parotid duct. Each alveolus is serous or albuminous as regards the nature of it secretion, and is composed of a basement membrane continuous with the wal of the duct, and surrounded by a plexus of capillaries. The alveolus is linec with polyhedral cells, which contain albuminous granules, and almost com pletely fill the tube, leaving only a small lumen. The first portion of the duct called the intercalary duct, is lined with flattened epithelium. Beyond this the





THE HEAD AND NECK


1289


becomes constricted into a neck, which is lined with cubical cells, these being

aced in the intralobular duct by columnar cells. These cells are granular irds the lumen of the tube, but striated in the outer part. Each of the larger

s is composed of a basement membrane, strengthened externally by a layer

onnective tissue, superadded to which there stratum of plain muscular fibres.

Development of the Salivary Glands. —The >tid is of ectodermal origin, the submandiband sublingual are derived from entoderm, y appear as solid outgrowths of the epiium of the buccal cavity, which grow into adjacent mesodermic connective tissue. The helial constituents of each gland are derived 1 the buccal lining, whilst the capsule and lective-tissue elements are of mesodermic in.

Each solid epithelial outgrowth ramifies t freely, and these ramifications, as well as primary outgrowth, become tubular. The owing process commences in the primary growth, and extends thence throughout its lerous ramifications. The primary outgrowth represents the principal duct ach gland, and the acini, or alveoli, appear as dilatations of the walls of the final ramifications.

rhe sublingual gland, from its numerous ducts, is to be regarded as a cluster

mall alveolo-lingual glands.

Appendages of the Eye.

The appendages of the eye consist of the eyelids and the lacrimal jaratus.

Eyelids. —The eyelids, or palpebrae, are two movable curtains placed front of the eyeball, to which they form an important protection.

inner surface of each is covered by mucous membrane, which stitutes the conjunctiva. The upper eyelid is larger than the lower, l, when closed, covers the transparent part of the eye or cornea, s also more movable than the lower, being provided with a special /ator muscle, the levator palpebrae superioris. The elliptical srval between the lids is called the palpebral fissure, and the lateral remities of this fissure are called the angles of the eye. The lateral lie (canthus) is formed by the junction between the two lids. At medial angle (canthus) the lids are separated by a recess, called lacus lacrimalis, in which there is a small body, called the caruncula rimalis. In this region the eyelids are separated from the eyeball a vertical, semilunar fold of the conjunctiva, called the plica semiaris. The margin of each eyelid shows, at the commencement of lacus lacrimalis, a slight conical elevation, called the papilla lacrilis, the apex of which presents a small orifice, termed the punctum rimale, its direction being towards the eyeball. Each punctum is entrance to a passage, called the lacrimal canaliculus, by which the rs are conveyed from the surface of the eyeball into the lacrimal , and thence, through the naso-lacrimal duct, into the inferior rtus of the nasal cavity.


Fig. 779. —Structure of the Parotid Gland.





1290


A MANUAL OF ANATOMY


The free margins of the eyelids, lateral to the puncta lacrima are provided with hairs, called the eyelashes. They are short, stc and curved, and are arranged in two rows. Those of the upper are more numerous and larger than those of the lower. The up eyelashes are curved upwards and the lower downwards, and in 1 manner intermingling is avoided. Within the lines of attachment the eyelashes there is a row of modified sweat-glands, known as ciliary glands (glands of Moll), the openings of which are associa with the follicles of the eyelashes, and with the condition known as s Structure of the Eyelids. —Each eyelid is composed of the follow structures, from before backwards:


1. Skin.

2. Subcutaneous tissue.

3. Palpebral fibres of the orbicularis

oculi.


4. Cellular tissue.

5. The tarsi.

6. Tarsal glands.

7. Conjunctiva.



Fig. 780.—A, to show the Reflection of Conjunctiva at Upper ani Lower Fornices; B, Plan of the Palpebral Fissure.

In addition to the foregoing structures the upper eyelid contc the tendinous insertion of the levator palpebrse superioris muscle.

The skin is very thin, and at the ciliary margins of the eye it becomes continuous with the conjunctiva, which is a mucous m< brane. The subcutaneous connective tissue is scanty and devoid fat, and in consequence the slightest contraction of the muscle cai a noticeable movement of the skin. The palpebral fibres of the orbi laris oculi form a very delicate, pale sheet. The cellular layer, d to the orbicularis oculi, is lax, and allows the muscle to move frc over the tarsal plate. The tarsus in each eyelid is composed of c( pact fibrous tissue. The upper tarsus is larger than the inferior, ; is semilunar, its depth at the centre being about J inch. Its up part gives insertion to the levator palpebrae superioris. The lo tarsus is narrow, and is almost of the same depth throughout. ciliary margins of the tarsi are free, straight, and comparatively th: The orbital margins are attached to the circumference of the orbit a membranous expansion, called the orbital septum. The upper


THE HEAD AND NECK


1291


the orbital septum (superior palpebral ligament) is attached above the upper part of the circumference of the orbit, where it blends h the periosteum, and below it blends with the tendon of insertion the levator palpebrae superioris on the upper , tarsus. The lower i of the orbital septum (inferior palpebral ligament) extends between

lower part of the circumference of the orbit and the lower margin

the lower tarsus.

Laterally and medially the tarsi are attached to the palpebral iments. The lateral palpebral ligament is formed by the junction the upper and lower parts of the orbital septum, and is attached the malar bone. The medial palpebral ligament is independent the orbital septum. Medially it is attached to the lateral surp of the frontal process of the maxilla in front of the lacrimal cus. From this point it passes horizontally outwards for about Uch, and then divides into two laminae, which are attached to the si of both eyelids. It passes in front of the lacrimal sac, giving an set, which passes behind the sac to be attached to the crest of the ripial bone. The ligament gives origin to a few fibres of the )icularis oculi.

The tarsal glands (Meibomian glands) are situated on the deep rface of each tarsus, and lie between the plate and the conjunctiva right angles to the ciliary margin. There are about thirty in the pef ej^elid and about twenty in the lower, and they are arranged in rallel rows, which occupy grooves on the ocular surface of each 'sus. Each gland opens by an independent orifice, and these orifices j arranged in a single row, lying a little behind the ciliary margin the eyelid.

Structure. —The tarsal glands are modified sebaceous glands, and their retiqn lubricates the margins of the eyelids, and prevents them from adhering, ch consists of a tube, closed at one end, and having its sides beset with r erticula. The wall of the tube is composed of a basement membrane, which lined with cubical epithelium throughout the greater part of the gland, but se tq the orifice this is replaced by stratified epithelium.

In fhe neighbourhood of the closed ends of the tarsal glands there 5 some convoluted tubules, which are known as the posterior tarsal mds f the orifices of which are placed close to the conjunctival fornix.

Conjunctiva. —This is the mucous membrane which covers the ular surfaces of the eyelids and the front of the eyeball. It consists two parts—palpebral and ocular.

The palpebral portion lines the ocular or deep surfaces of the elids, and at their ciliary margins it is continuous with the skin on eir outer surfaces. It is also continuous through the puncta lacrialiq, with the lining membrane of the lacrimal canaliculi, lacrimal c, naso-lacrimal duct, and inferior meatus of the nose. In the region the medial angle of the eye it gives rise to the plica semilunaris, and at e outer part of the upper eyelid it is continuous with the lining embrane of the lacrimal ducts. The palpebral portion is fairly thick id highly vascular, and it has numerous papillae.


1292


A MANUAL OF ANATOMY


The ocular portion consists of two portions—sclerotic and cornea It is continuous with the palpebral portion, and the line of reflectic from the eyelids is known as the conjunctival fornix, superior ar inferior respectively. Here the orifices of the posterior tarsal glanc are met with. The conjunctiva is loosely connected to the scler; and is thin, non-papillary, transparent, and contains only a fe bloodvessels, the whiteness of the sclera being unaffected by it.

The palpebral portion is covered by columnar epithelium, whic at the ciliary margin passes into the stratified epithelium of the skir the sclerotic portion is also covered by columnar epithelium, but tl corneal part is represented by the stratified epithelium of the corpe;

The conjunctiva is supplied with blood by offsets from the palpebr; branches of the ophthalmic artery and its lacrimal branch. Tt vessels are disposed in a tortuous manner, and are movable upon tl eyeball when the conjunctiva is pressed upon and displaced. TI nerves are numerous, and form plexuses. The lymphatics begin clos to the corneal margin in a network, from which vessels proceed to network in each evelid behind the tarsus. The efferent vesse. ultimately reach the parotid and submandibular lymph glands.

The caruncuia lacrimalis occupies the lacus lacrimalis in the regio of the medial angle of the eye. It is a small, reddish, spong body, consisting of a detached portion of skin containing modifie .sweat and sebaceous glands. The latter open into the follicles of ver delicate hairs with which the surface of the caruncle is provided, an they furnish the white secretion which may accumulate at the medic angle.

The plica semilunaris is a vertical, semilunar fold of the conjunctiv which is situated on the outer side of the caruncle, its concave margi: being directed outwards. It corresponds to the membrana nictitam or third eyelid, of some animals.

Development of the Eyelids and Tarsal Glands.— The eyelids make thei appearance as two folds of skin, above and below the developing eyeball. Eac fold contains some mesodermic tissue which gives rise to the connective-tissu element and tarsus of the lid, muscle cells extending into the lids later from th platysma sheet. The ectoderm of the posterior surfaces of the lids acquires th characters of mucous membrane, and forms the conjunctival epithelium. In th course of the third month the eyelids grow together and unite along their margins a space being thereby enclosed between the lids and the front of the developin eyeball. The union affects the epithelium only, and persists until near the em of intra-uterine life.

During the period of fusion of the eyelids the tarsal glands and the cilia o eyelashes are formed. The tarsal glands are developed from the epitheliur along the line of fusion of the lids. Solid rods of epithelial cells are formei which grow into the mesodermic tissue of the two lids and give off lateral prc cesses. These solid rods become hollow, and so form the tarsal glands. Som of the epithelial rods give rise to the ciliary glands. A short time before birt the eyelids become separated, and the palpebral fissure is thereby formed.

The plica semilunaris is developed as a vertical fold of conjunctiva near th medial angle of the eye, external to the caruncle, but it attains little developmen in man.

The caruncle is developed from that portion of the margin of the lowe




THE HEAD AND NECK


1293


?lid which intervenes between the inferior punctum lacrimale and the medial y\e. The tarsal glands in this region become modified, and the tissue conning these modified glands becomes raised, and forms the reddish, spongy

•uncle.

Lacrimal Apparatus.—The constituent parts of the lacrimal paratus are as follows:

1. The lacrimal gland. 3. The lacrimal sac.

2. The lacrimal canaliculi. 4. The naso-lacrimal duct.

The lacrimal gland will be found described on p. 1247.

The lacrimal canaliculi are two in number, superior and inferior, ley commence at the puncta lacrimalia on the summit of the papillae

rimales, which latter are situated on the ciliary margins of the

elids close to the lacus lacrimalis. The superior canaliculus at first cends vertically for about T V inch, after which it makes a sudden


Tarsal Glands


Lacrimal Gland Lacrimal Ducts


Plica Semilunaris


Superior Punctum Lacrimale ! Caruncula Lacrimalis

Superior Lacrimal Canaliculus


•V. Lacrimal Sac

it

4

rjsL Inferior Lacrimal Canaliculus Naso-lacrimal Duct


Inferior Punctum Lacrimale

Fig. 781. — The Lacrimal Apparatus of the Right Eye.

The tarsal glands of the upper eyelid are also shown.

tid, and passes inwards and downwards to the lacrimal sac. The ierior canaliculus at first descends vertically for about T \ inch, after lich it makes a sudden bend, and passes almost horizontally inwards the lacrimal sac. The tw r o canaliculi open into the lacrimal sac, her close together or by a common orifice, and their mucous memane is lined with stratified squamous epithelium. The two slips the lacrimal portion of the orbicularis oculi are closely related to the rizontal portions of the canaliculi.

The lacrimal sac is the dilated upper part of the passage by which 2 tears are conveyed from the lacrimal canaliculi to the inferior iatus of the nose. It occupies the lacrimal groove of the lacrimal ne and frontal process of the maxilla. Above it has a round, closed tremity, and below it opens into the naso-lacrimal duct. Externally receives the lacrimal canaliculi separately or conjointly, and in front is crossed by the medial palpebral ligament. Behind it is related the lacrimal part of the orbicularis oculi.





1294


A MANUAL OF ANATOMY


The naso-lacrimal duct (nasal duct) extends from the lower end the lacrimal sac to the anterior part of the inferior meatus of the n< under cover of the front part of the inferior nasal concha. Its len^ is about f inch, and its diameter about ^ inch. It is directed dov wards, outwards, and backwards, and its opening into the anterior p; of the inferior meatus of the nose is usually guarded by an imperfi mucous fold, known as the lacrimal fold (valve of Hasner). The na orifice of the duct is about ij inches from the anterior nasal apertur

Structure of the Lacrimal Sac and Naso-lacrimal Duct. —The wall is compo of fibro-elastic tissue, which adheres closely to the periosteum of the boi and is covered by mucous membrane. The epithelial lining is of the colum variety, and at intervals the cells are furnished with cilia. The mucous m( brane is continuous superiorly with the conjunctiva through the lacrimal car iculi and puncta, and inferiorly it is continuous with the nasal mucous membra In the naso-lacrimal duct it may present one or two folds.

Development of the Naso-lacrimal Duct and its Appendages. —The effer lacrimal apparatus consists of (i) the lacrimal canaliculi, (2) the lacrimal s and (3) the naso-lacrimal duct.

In the course of the development of the face, the maxillary process and lateral nasal process of either side are separated by a groove which extei from the inner angle of the eye to the olfactory pit. This groove is called naso-optic, or oculo-nasal groove, and it indicates deeply the position of lacrimal duct. In the bottom of this groove a solid epithelial cord makes appearance, which, becoming hollow, forms the naso-lacrimal duct. The up extremity of the duct bifurcates, its two divisions becoming connected w the margins of the eyelids near their inner ends, and forming the lacrimal cai iculi. The lower end of the naso-lacrimal duct at a much later period opens i the lower part of the nasal cavity. The lacrimal sac is the upper expam extremity of the naso-lacrimal duct.


Auricle.

The auricle, or pinna, is that part of the external ear which proje from the side of the head. It has two surfaces, outer and inner.

The outer surface is irregularly concave, and about its centre th is a large deep fossa, called the concha of the auricle, which leads the external auditory meatus. Towards the upper and anterior p of the concha there is an elevation, called the crus of helix, whicl directed upwards and forwards to the anterior border of the auri< The concha is thus divided into two parts, upper and lower. In fr< of the concha there is a small, somewhat conical prominence, called tragus, which projects slightly backwards over the orifice of external auditory meatus, and is provided with hairs on its in: aspect. A short distance behind the tragus, and on a lower le than it, there is another prominence, called the antitragus, whicl separated from the tragus by a deep notch, called the intertragic not The skin over the antitragus is also provided with hairs. Below antitragus and intertragic notch is the most dependent part of auricle, called the lobule, which is comparatively soft in consister The prominent rim of the auricle is called the helix. It is incurv and begins at the upper and front part of the concha in the crus


THE HEAD AND NECK


1295


e helix, already referred to. It then surrounds the margin of the hide, and ends below in the back part of the lobule. In some cases e auricular tubercle (Darwin’s tubercle) is situated on the incurved argin slightly above the level where the antihelix, to be presently iscribed, bifurcates into its crura. This projection is well developed the ears of quadrupeds, and forms the point or tip. A short distance [thin the helix there is another curved elevation, called the anti>lix. This begins at the back part of the antitragus and ascends

hind the concha, above which it divides into two diverging crura,

)per and lower. Between the helix and the antihelix is an elongated, irrow fossa, called the scaphoid fossa, and between the diverging ura of the antihelix there is a depression, called the triangular fossa.


Auricular Tubercle


Scaphoid Fossa -/--

Helix


Antihelix


Concha/


Superior Crus of Antihelix Fossa Triangularis

Helix


'—;'r - Inferior Crus of Antihelix


- - Crus of Helix -Tragus

'-Orifice of External Auditory Meatus


‘'Intertgraic Notch "'■Antitragus


Lobule


Fig. 782. —The Right Auricle (Lateral Surface).


The inner or cranial surface of the auricle presents convexities irresponding to the fossae on the outer surface, the convexity opposite le concha being especially prominent.

Structure Of the Auricle. —The auricle, with the exception of the lobule, is mposed of a plate of yellow elastic fibro-cartilage covered by skin. This ate imparts firmness and elasticity to it, and is provided with ligaments and trinsic muscles. The skin is thin, and adheres closely to the fibro-cartilaginous ate. It is provided with hairs, which are most plentiful in the regions of the agus and antitragus. The cartilage of the auricle is rolled upon itself so as to rm the outer or cartilaginous part of the external auditory meatus. This >rtion of it is attached medially to the external auditory process of the temporal >ne by fibrous tissue. The rolled or tubular portion has a deficiency at the iterior and upper part, between the tragus and the helix, which is occupied by fibrous membrane. It has also a variable number of transverse clefts, which e filled with fibrous tissue. The lower extremity of the cartilage of the helix separated from the cartilage of the antihelix by a deep cleft. The part of the rtilage of the helix behind this cleft is known as the tail of the helix. At the >per and anterior part of the auricle, where the helix begins to curve backwards, e cartilage has a small sharp projection called the spine of the helix.




1296


A MANUAL OF ANATOMY


Ligaments of the Auricle.—These are anterior and posterior. ' anterior ligament extends from the spine of the helix to the zygonu the temporal bone close to its root. The posterior ligament extei from the cranial aspect of the concha, under cover of the auricul; posterior, to the mastoid process.

Intrinsic Muscles.—These muscles, which are very thin and p; are confined to the auricle, and are six in number, four being situa on the outer surface and two on the inner surface.

Muscles on Outer Surface.—These are: (1) the helicis major; (2) helicis minor; (3) the tragicus; and (4) the antitragicus.


Auricuiaris Anterior Helicis Major

Helicis Minor


--Auricuiaris Superior


^Auricuiaris Posterior


> Tail of Helix

1

Antitragicus


Fig. 783.—The Outer Surface of the Left Auricular Cartilage and

Muscles (Arnold).


The helicis major extends from the spine of the helix along i anterior part of the helix as high as the level at which it curves bat wards.

The helicis minor lies upon the crus helicis.

The tragicus lies upon the outer surface of the tragus, its fib: being almost vertical.

The antitragicus extends from the outer surface of the antitrag backwards and slightly upwards, to be attached to the tail of the hel

Muscles on Inner Surface.—These are: (1) the transversus auricn and (2) the obliquus auriculae.

The transversus auriculae extends over the depression which cor sponds to the antihelix on the outer surface, its attachments being






THE HEAD AND NECK


1297


convexity of the concha on the one hand, and the convexity of the a of the helix on the other.

The obliquus auriculae extends over the depression corresponding he lower crus of the antihelix on the outer surface.

Action of the Intrinsic Muscles.—The tragicus and antitragicus inish the orifice of the external auditory meatus, and the muscles of helix, major and minor, have an opposite effect.

Blood-supply of the Auricle.—The arteries are derived from (1) the terior auricular branch of the external carotid, (2) the anterior icular branches of the superficial temporal, and (3) the deep auricular nch of the first part of the maxillary, the last named giving offsets he cartilaginous part of the external auditory meatus.


, 784. —The Inner Surface of the Left Auricular Cartilage and its

Muscles (Arnold).

The veins end in the posterior auricular, superficial temporal, and xillary veins, and one or two of them may open into the mastoid issary vein.

The lymphatic vessels of the inner surface of the auricle pass chiefly the mastoid lymph glands; but a few end in the superior deep viced lymph glands. The lymphatics of the lobule pass to (1) the 'erficial cervical lymph glands, and (2) the superior deep cervical lph glands. The lymphatics of the outer surface of the auricle pass

he superficial parotid lymph glands.

Nerve-supply.—The inner surface receives three cutaneous nerves. 5 great auricular supplies about the lower three-fourths, the lesser ipital about the upper fourth, and the auricular branch of the vagus

82










1298


A MANUAL 'OF ANATOMY


supplies the integument over the convexity of the concha. The oui surface is supplied by two cutaneous nerves. The auriculo-tempoi nerve supplies the upper two-thirds, and the great auricular suppli the lower third. The motor nerve of the intrinsic muscles is the fac nerve.

The Nose.


The nose has a root, situated below the glabella of the frontal bor an apex (tip), situated interiorly; and the dorsum nasi, which occup] an intermediate position. The upper part of the dorsum is kno\ as the bridge of the nose. At the lower part of the nose there are t openings of the nostrils, or nares. The outer margin of each nost is slightly prominent and curved, and is called the ala. The nostr are separated from each other by a septum, called the columna na which, as well as the ala, is composed of fibrous tissue and skin. With the circumference of each nostril there are several stout hairs or vibriss

The superficial or facial aspect of the nose derives its arteries frc (1) the lateral nasal branches of the facial, (2) the dorsal nasal bran of the ophthalmic, and (3) the infra-orbital branch of the maxillary.

The nerves are derived from the naso-ciliary and infra-orbil nerves, the branches from the naso-ciliary being the infratrochlear ai the terminal cutaneous offsets.

The cutaneous lymphatics of the root of the nose pass to the supt ficial parotid lymph glands. Those from the greater part of the na< integument pass to the submandibular lymph glands, the lymph glan forming gland-stations in their path.

The framework of the nose is both osseous and cartilaginous.

Cartilages of the Nose.—The na<


cartilages are five:


Nasal Bone


Frontal Process of Maxilla


Upper nasal cartilage. Lower nasal cartilage. Septal cartilage.


Upper Nasal Cartilage Septal Cartilage


Small Alar Cartilages


^ 'V '

Subcutaneous Fat


The upper nasal cartilages (upp lateral cartilages) are situated imir diately below the nasal bones. Th are triangular, and their anten borders are continuous with ea other, and with the anterior marg of the septal cartilage, in each ca superiorly. Inferiorly, the anteri borders are separated by a slig interval, in which the anterior m£ gin of the septal cartilage is visible. The posterior border of ea cartilage is attached to the lower sloping border of the nasal bone, a: also to the upper part of the nasal notch on the medial border of t maxilla. The lower border is connected by fibrous tissue to the upp margin of the lower nasal cartilage.


Lower Nasal Cartilage

Fig. 785.—The Cartilages of the Nose (Anterior View) (Arnold).





THE HEAD AND NECK


1299


The lower nasal cartilages (lower lateral cartilages) are situated )w the upper pair, and each is bent so as to lie in front and on each j of the nostril, which it keeps open. Its outer portion is called lateral process, and its inner portion the septal process.


Small Cartilages of Ala


'ig. 786.—The Cartilages of the Nose (Lateral Aspect) (Arnold).

The lateral process is attached by fibrous tissue to the upper nasal tilage, and to the lower part of the nasal notch on the medial border the maxilla. The septal process is folded backwards, and touches fellow of the opposite side. It lies along the upper part of the umna nasi, and along the antero-inferior border of the septal cartie. Anteriorly it is separated from its fellow by a notch.

In the fibrous tissue which con:ts the lateral process to the .xilla two or more isolated porns of cartilage are met with, led the small cartilages of the ala inor cartilages).

Development. —The upper and lower >al cartilages are developed in the sral nasal process.

The septal cartilage is medially teed, and is usually inclined slightly one side, most frequently the left, forms a large part of the nasal )tum anteriorly, and has the form an irregularly four-sided, latery compressed plate. Its anterior border is attached to the back of e nasal bones, along the course of the internasal suture; below this is connected to the anterior borders of the upper nasal cartilages,


Lower Nasal Cartilages


A _ Septal Process

' Lateral Process

Anterior Aperture


J Small Cartilages of Ala


Subcutaneous Fat


Septal Cartilage

Fig. 787. — The Cartilages of the Nose (Inferior Aspect) (Arnold).





1300


A MANUAL OF ANATOMY


and below these it lies between the septal processes of the lower na cartilages. Its posterior border is accurately applied to the irregu anterior margin of the perpendicular plate of the ethmoid bone. inferior border is received into the front part of the groove on the antei border of the vomer. The antero-inferior border passes upwards a forwards from the front part of the inferior border to the antei border. In early life the septal cartilage is prolonged backwards


~T Frontal Sinus


Sphenoidal Sinus


-Nasal Bone


Perpendicular Plate of Ethmoid


Horizontal Plate of Palatine Bone (in section)


\ Septal Process of Lc \ Nasal Cartilage Septal Cartilage Womero-nasal Cartilage


Vomer


Palatine Process of Maxilla (in section)


Fig. 788. —The Osseous and Cartilaginous Nasal Septum (Right

Lateral Aspect).


the body of the sphenoid bone in the form of a narrow strip, whi intervenes between the lower border of the perpendicular plate the ethmoid and the vomerine groove. This portion is known the sphenoidal process. Along the inferior border of the sepi cartilage, between it and the anterior border of the vomer, there 2 two narrow, elongated strips of cartilage, right and left, which £ called the vomero-nasal cartilages (cartilages of Jacobson).

Development. —The septal cartilage is derived from the chondrocranium.








THE HEAD AND NECK


1301


The Temporal and Infratemporal Regions.

Muscles of Mastication. —These are four in number—namely, the

seter, temporal, lateral pterygoid, and medial pterygoid.

Masseter — Origin —(1) Superficial Portion. —The anterior twods of the lower border of the zygomatic arch. (2) Deep Portion, he posterior third of the lower border, and the whole of the medial 'ace of the zygomatic arch.


Orb. Oculi


Orb. Oris

Masseter

Buccinator


Mandible


Ext. Carotid


Platysma


Fig. 789.—The Masseter Muscle.

Insertion .—The superficial portion is inserted into the lower margin d the deep portion into the upper half of the outer surface of the nus of the mandible. The superficial fibres extend as far as the E*le, and the deep fibres encroach on the coronoid process. Nerve-supply .—The masseteric branch of the anterior portion of p mandibular division of the trigeminal nerve. This branch leaves

pterygoid region by passing over the mandibular notch of the

nus of the mandible below the zygoma, and it therefore enters the iscle on its deep surface accompanied by the masseteric artery.

The superficial portion of the muscle is directed downwards and







1302


A MANUAL OF ANATOMY


slightly backwards, and the deep portion downwards and very sligl forwards.

Action. —To elevate the mandible. The superficial portion ; draws it slightly forwards.

Relations — Superficial. —The parotid gland and its duct, branc of the facial nerve, the transverse facial artery, the risorius, and platysma. Deep. —The ramus of the mandible, and the masset nerve and artery. The anterior border overlaps the buccinator, fi which it is separated by the suctorial pad of fat.

Temporalis — Origin. —(i) The temporal fossa, extending as higl the inferior temporal line of the frontal and parietal bones, and as as the infratemporal crest on the external surface of the greater w of the sphenoid, but excluding the portion of the fossa formed by zygomatic bone; and (2) the deep surface of the temporal fascia 0 its upper part.

Insertion. —(1) The medial surface, summit, and anterior bor of the coronoid process of the mandible; and (2) the elongated triangi surface on the medial surface of the ramus of the mandible, close wit the anterior border, and extending as low as a point on the inner «  of the last molar socket. w Nerve-supply. —The deep temporal nerves, usually three in numl which are branches of the anterior portion of the maairitofcv divis of the trigeminal nerve, and which enter the deep surface of the mus

The muscle is fan-shaped. The anterior fibres descend aim vertically; the middle fibres pass obliquely downwards and forwai and the posterior fibres pass forwards almost horizontally.

Action. —To raise the mandible, as in closing the mouth, posterior fibres also retract the mandible, and act in opposition to lateral pterygoid, which protracts it.

Relations — Superficial. —The temporal fascia, supporting the auri lares anterior et superior; the superficial temporal artery, aurici temporal nerve, and temporal branches of the facial nerve; the zygor and fat, which is continuous with the suctorial pad. Deep — 1 temporal fossa, the deep temporal arteries and nerves, and the late pterygoid muscle.

The buccal nerve passes downwards and forwards under cover the muscle close to the anterior border of the ramus of the mandil and the masseteric nerve and artery pass outwards close to the poster border in the region of the mandibular notch.

For the temporal fascia, see p. 1161.

Lateral Pterygoid (External Pterygoid) — Origin — (1) Upper Head

The infratemporal surface and infratemporal crest of the greater w of the sphenoid. (2) Lower Head. —The outer surface of the late pterygoid plate of the sphenoid. The upper head is small, and the lo\ head is of large size.

Insertion. —(1) The depression on the front of the neck of 1 mandible; and (2) the front of the articular capsule and disc of 1 mandibular joint.


THE HEAD AND NECK


1303


Nerve-supply. —The nerve to the lateral pterygoid, from the anterior ision of the mandibular nerve.

The direction of the muscle is backwards and slightly outwards. Action. —(1) To draw forwards the neck and condyloid process of

mandible, and also the articular disc. When the muscles of opposite

es act in concert the mandible is protruded, and the lower incisor 1 canine teeth project beyond the level of those of the maxilla. The scles of opposite sides, however, usually act alternately and thus >duce the oblique or grinding movement, the lower molars of one e being carried forwards and inwards under the corresponding per molars, and vice versa. At the same time the elevators of the ndible are in action. (2) To take part in opening the mouth by iwing the condyloid process of the mandible and articular disc forrds on to the articular eminence of the temporal bone. The lateral


Buccal Nerve (cut)


Lower Head of Lateral Pterygoid

^Pterygomandibular

Ligament

•Parotid Duct


Buccinator


Medial Pterygoid


Fig. 790. —The Pterygoid and Buccinator Muscles.


srygoid is antagonistic to the posterior portion of the temporalis iscle.

Relations — Superficial. —Part of the ramus of the mandible, the ver part of the temporalis, part of the pterygoid plexus of veins, the [ccal nerve, and perhaps the second part of the maxillary artery. lep. —The upper portion of the medial pterygoid muscle, the sphenomdibular ligament, in some cases the second part of the maxillary tery, the middle meningeal artery, a part of the pterygoid plexus of ins, the mandibular nerve, the otic ganglion, and the chorda tympani rve. Superior. —The masseteric and deep temporal nerves. Inferior. The inferior dental and lingual nerves, and the spheno-mandibular

ament. The buccal nerve, with the anterior deep temporal nerve,

akes its appearance between the upper and lower heads, and the axillary artery may sink between them.





1304


A MANUAL OF ANATOMY

Medial Pterygoid (Internal Pterygoid) — Origin. —(1) The inner surfs of the lateral pterygoid plate of the sphenoid, and the portion of t tubercle of the palatine bone which forms the lower part of the pterygc fossa; and (2) the outer surface of the tubercle of the palatine boi and the adjacent portion of the tuberosity of the maxilla.

Insertion. —(1) The inner aspect of the angle of the mandib and (2) the back part of the inner surface of the ramus, between t angle and the mandibular foramen.

Nerve-supply .—The medial pterygoid branch of the anterior port! of the mandibular nerve.

The direction of the muscle is downwards, backwards, and 01 wards.

Action.—{ 1) To elevate the mandible; and (2) to draw it forwarc

Relations- — Superficial .—The lateral pterygoid muscle to a slig extent superiorly, the spheno-mandibular ligament, the maxillary ai inferior dental vessels, and the inferior dental and lingual nervt

Deep .—The tensor palati muscle, and the superior constrictor muse of the pharynx.

For a description of the spheno-mandibular ligament, see p. 1316.

The Maxillary Artery (Internal Maxillary Artery) .—This vessei the larger of the two terminal branches of the external carotid, arises from that artery opposite the neck of the mandible and within tl parotid gland. Its course is at first forwards and inwards behind tl neck of the mandible, and superficial to the spheno-mandibular lig ment. It then inclines upwards and forwards through the infr; tempoial fossa, usually passing superficial to the lateral ptervgoi muscle, though in many cases it passes deep to it. Having reached tl interval between the two heads of the lateral pterygoid, it sinks deep] between them, and, passing through the pterygo-maxillary fissure, enters thepterygo-palatine fossa, where it gives off its terminal branche In those cases in which the artery passes deep to the lateral pterygoi muscle it forms a piojecting curve between the two heads of the muscl The course of the vessel is very tortuous in adaptation to the mobilit of the surrounding structures.

Owing to its complexity it is convenient to divide the artery inf thiee parts. The first or mandibular part is situated between tb neck of the mandible and the spheno-mandibular ligament, and it course is horizontally forwards and inwards. It is accompanied b the maxillary vein, and lies along the back part of the lower border c the lateral pterygoid muscle, crossing in front of the inferior dents nerve and embedded in the parotid gland. The second or pterygoi part usually lies superficial to the lower head of the lateral ptervgoic and under cover of the insertion of the temporalis. Its course througi the infratemporal fossa is upwards and forwards, and it sinks betweei the two heads of the lateral pterygoid on its way to the pterygo maxillary fissure. In many cases, however, the second part of th< vessel passes deep to the lower head of the lateral pterygoid, crossing m front of the medial pterygoid muscle and lingual nerve. Unde:


THE HEAD AND NECK 1305

e circumstances it forms a projecting curve between the two

is of the lateral pterygoid beneath the long buccal nerve. The i or pterygo-palatine part is situated in the pterygo-palatine fossa, ch it enters by passing through the pterygo-maxillary fissure. In fossa the vessel and its branches are intimately related to the ciliary nerve and the spheno-palatine ganglion, with its branches.


F ig . 791.— The Maxillary Artery and its Branches.

ramus of the mandible and one half of the calvaria have been removed. 1, lateral pterygoid muscle; 2, medial pterygoid muscle.

Branches. —These are as follows:

First Part.

p auricular.
erior tympanic,

idle meningeal, giving if accessory meningeal, srior dental.


Branches of the First Part.— The deep auricular artery, of small s, ascends within the parotid gland just behind the mandibulai it, and pierces the anterior cartilaginous wall of the external auditory atus. It supplies the cutaneous lining of that passage and .the ter surface of the tympanic membrane.


Second Part.

Masseteric.

Pterygoid.

Posterior deep temporal. Anterior deep temporal. Buccal.


Third Part.

Posterior superior dental.

Infra-orbital.

Greater palatine. Artery of the pterygoid canal.

Pharyngeal.

Spheno-palatine.








1306


A MANUAL OF ANATOMY


The anterior tympanic artery may be associated with the precedi at its origin. It ascends beneath the lateral pterygoid, and enters 1 tympanic cavity by passing through the squamo-tympanic fissu It is distributed to the structures within the tympanic cavity and the inner surface of the tympanic membrane. Around the circu ference of that membrane it forms an arterial ring with an offset the stylo-mastoid artery, which is a branch of the posterior auricula The middle meningeal artery, of large size, ascends beneath 1 lateral pterygoid muscle, and, passing between the two roots of ori$ of the auriculo-temporal nerve, it enters the cranial cavity throu


Deep Temporal Vessels and Nerves


Middle Meningeal Artery


Sph. Max. Fossa

Buccal A. and N.


Lingual N.

Sph. Mand. Lig.

Inf. Dental N. and A.


Sup. Constrictor


Fig. 792.—Dissection of Right Pterygoid Region.


the foramen spinosum in the sphenoid bone. It then passes upwar and forwards to the inner aspect of the antero-inferior angle of t] parietal bone, where it divides into two branches, anterior ai posterior, which ramify in the branching grooves on the inner surfa of the parietal bone. The artery is accompanied by a plexus sympathetic nerves, but its vein passes through the foramen oval For the distribution of the vessel within the cranium, see p. 159 Before disappearing through the foramen spinosum the midd meningeal artery usually gives off the accessory meningeal artery, whi< enters the cranial cavity through the foramen ovale.








THE HEAD AND NECK


1307


The inferior dental artery arises nearly opposite the middle meningeal ery, and descends upon the spheno-mandibular ligament in company

h the inferior dental nerve, lying on its posterior and outer side.

,ving reached the mandibular foramen, it gives off the small mylorid branch y and then it passes through the mandibular foramen and

ers the mandibular canal, which it traverses as far as the level

the mental foramen, where it ends by dividing into its mental and

isor branches. Within the mandibular canal the artery is accomnied by the inferior dental nerve and inferior dental vein.

Branches. —-The mylo-hyoid branch, of small size, arises at the r el of the mandibular foramen. In company with the mylo-hyoid rve it pierces the spheno-mandibular ligament, and descends in 3 mylo-hyoid groove to be distributed to the under surface of the do-hyoid muscle. The molar, premolar, and canine branches arise thin the mandibular canal, and supply the pulps of these teeth, Lich they reach by passing through the foramina on the extremities their fangs. Th e mental branch leaves the mandibular canal through s mental foramen, and has been already described (see p. 1283). ie incisor branch supplies the pulps of the incisor teeth of one side. Branches of the Second Part. —The branches of this part are muscular their distribution. The masseteric artery passes outwards, with the □responding nerve, over the mandibular notch, and enters the deep rface of the masseter. The pterygoid branches are distributed to e corresponding muscles. The posterior and anterior deep temporal teries pass upwards to the posterior and anterior parts of the temporal ssa beneath the temporalis. They supply the muscle and the bones rming the fossa, and anastomose with the middle temporal artery, lich is a branch of the superficial temporal. The anterior deep mporal artery also anastomoses with the lacrimal artery by twigs tiich pass through minute foramina in the outer wall of the orbit, le buccal artery passes downwards and forwards in company with e buccal nerve, and is distributed to the buccinator muscle and the lccal mucous membrane which lines it internally.

Branches of the Third Part.— The posterior superior dental artery ises from the maxillary as it is about to pass through the pterygoaxillary fissure into the pterygo-palatine fossa, and is sometimes isociated with the infra-orbital artery at its origin. It descends ion the zygomatic surface of the maxilla posterior to the zygomatic 'ocess, and its principal branches traverse the posterior dental canals > supply the pulps of the upper molar teeth of one side. It also irnishes twigs to the mucous lining of the maxillary sinus and to the 1m.

The infra-orbital artery arises in the pterygo-palatine fossa, somemes in common with the posterior superior dental. It passes through ie inferior orbital fissure in company with the maxillary nerve, and averses the infra-orbital groove and canal on the floor of the orbit, ie accompanying nerve being now called the infra-orbital nerve, rom this canal it emerges through the infra-orbital foramen on to


- 1308


A MANUAL OF ANATOMY


the face, where it has been already described (see p. 1282). The arter is accompanied by the infra-orbital vein. As the artery traverse the infra-orbital canal it furnishes (1) orbital branches to the structure on the floor of the orbit; and (2) the anterior superior dental branch which descends in the anterior dental canals in the maxilla, in compan with the corresponding nerves, to supply the pulps of the upper premok ingisor and canine teeth, and the mucous lining of the maxillary sinu:

The greater palatine artery (descending palatine artery) pass( downwards in the greater palatine canal, in company with the greatc palatine nerve, to the hard palate, where it passes forwards and in ware to the incisive fossa. In this situation it furnishes a branch whic ascends through the incisive canal, to anastomose with a branc of the spheno-palatine artery. As the artery traverses the greate palatine canal it gives off the lesser palatine arteries, which accompan corresponding nerves in the lesser palatine, canals, and supply the sol palate and tonsil.

The artery of the pterygoid canal (Vidian artery) passes backward through the pterygoid canal in company with the correspondin nerve, and its branches are: (1) to the upper part of the pharynx (2) to the pharyngo-tympanic tube; and (3) to the tympanum.

The pharyngeal branch (pterygo-palatine artery), of small siz< passes backwards through the pharyngeal canal in company with th pharyngeal branch of the spheno-palatine ganglion, and is distribute to the upper part of the pharynx, the pharyngo-tympanic tube, and th mucous lining of the corresponding sphenoidal sinus.

The spheno-palatine artery enters the superior meatus of the nasa cavity through the spheno-palatine foramen. Its branches are dis tributed extensively on the outer wall of the nasal cavity, and suppt the mucous membrane of the maxillary, ethmoidal, and frontal sinuses One branch, called the posterior septal (naso-palatine artery), descend upon the septum to the incisive canal, where it anastomoses with th terminal ascending branch of the greater palatine artery.

Pterygoid Plexus of Veins. —This is a large plexus which surround the lateral pterygoid muscle. Its tributaries correspond for th most part to the branches of the maxillary artery, and are chief!; as follows: the deep auricular, anterior tympanic, two middle menin geal, inferior dental, masseteric, pterygoid, deep temporal, bucca] superior dental, infra orbital, greater palatine, and spheno-palatine The blood is conveyed away from the plexus by two veins—namely the maxillary and the deep facial.

The maxillary vein (internal maxillary vein) is a short vessel whic] issues from the posterior part of the plexus, and accompanies th< first part of the maxillary artery. Opposite the neck of the mandibl it joins the superficial temporal vein within the parotid gland t( form the posterior facial vein.

The deep facial vein issues from the anterior part of the ptery goid plexus, and, passing downwards and forwards, it emerges deej to the mandibular ramus and masseter muscle, and joins the anterio:


THE HEAD AND NECK


1309,

ial vein on the buccinator muscle. The pterygoid plexus comnicates with the intracranial cavernous sinus by means of emissary ns, which pass through the foramen ovale, the emissary sphenoidal amen, and foramen lacerum; it communicates with the inferior - . ithalmic vein at the inferior orbital fissure and with the pterygoid TT _ yus behind and below. (a£jv*-$ <? )

Deep Facial Lymph Glands (Internal Maxillary Lymph Glands).—

ese glands lie upon the lateral pterygoid muscle. Their afferent >sels are derived from (1) the infratemporal and temporal fossae; 7 the orbit; (3) the palatal mucous membrane; (4) the nasal cavity part; (5) the cerebral dura mater; and (6) the tympanic cavity, eir efferent vessels pass to (t) the deep parotid lymph glands, and the superior deep cervical lymph glands.

Mandibular Nerve (Inferior Maxillary Nerve). —This is the third ision of the trigeminal nerve. It is a mixed nerve, and consists two roots—sensory and motor. The sensory root, which is of large e, arises from the trigeminal ganglion, and the motor root represents i entire motor root of the trigeminal nerve. Both roots leave the inial cavity through the foramen ovale, and immediately after their it they unite to form a mixed nerve—that is to say, a nerve composed both sensory and motor fibres. This nerve is very short, and lies eply in the infratemporal fossa, under cover of the lateral pterygoid iscle, where it gives off two branches—namely, the nervus spinosus d the nerve to the medial pterygoid muscle. Then it immediately saks up into two parts, known as the anterior and posterior trunks. ie nervus spinosus enters the cranial cavity through the foramen inosum, along with the middle meningeal artery, and divides into 0 branches—anterior and posterior. The anterior branch is stributed to the adjacent dura mater, and the posterior branch sses through the fissure between the petrous and squamous parts the temporal bone, to be distributed to the mucous lining of the istoid air-cells. The nerve to the medial pterygoid muscle arises from e deep surface of the undivided mandibular nerve, and passes downirds to enter the deep surface of the medial pterygoid muscle.

3se to its origin it. is intimately related to the otic ganglion.

Anterior Trunk of the Mandibular Nerve. —Ihis division is smaller an the posterior, and is principally motor in function, the only nsory branch furnished by it being the buccal nerve. Its branches e: (1) masseteric, furnishing the posterior deep temporal; (2) middle ep temporal; and (3) buccal, giving off the lateral pterygoid and terior deep temporal, after which it is purely sensory.

The masseteric nerve passes upwards deep to the upper head of e lateral pterygoid muscle, where it furnishes the posterioi deep mporal nerve. It then passes outwards over the upper bordei of e lateral pterygoid, and over the mandibulai notch behind the mporalis, to enter the upper part of the masseter on its deep surface.

The deep temporal nerves are three in numbet anterior, middle, id posterior. The anterior deep temporal nerve usually arises from


i3io


A MANUAL OF ANATOMY


the buccal after it has passed between the two heads of the latei pterygoid. It runs upwards superficial to the upper head of th muscle, and enters the anterior part of the temporalis muscle on i deep surface. The middle deep temporal nerve is a direct bran* of the anterior trunk of the mandibular, and it ascends beneath t] lateral pterygoid to enter the middle part of the temporalis on i deep surface. The posterior deep temporal nerve springs from t] masseteric nerve beneath the upper head of the lateral pterygoi


Fig. 793- The Nerves of the Temporal and Mandibular Regions

(Hirschfeld and Leveille).

i, temporalis; 2, lateral pterygoid; 3, medial pterygoid; 4, masseter;

5, buccinator.

and, passing upwards, it enters the posterior part of the temporal on its deep surface.

The buccal nerve {long buccal nerve ) passes outwards betwee the two heads of the lateral pterygoid, and then downwards an' forwards in contact with the inner surface of the temporalis at it insertion. Having emerged from deep to the mandibular ramus an' anterior border of the masseter, it is received upon the outer surfac of the buccinator, where it communicates with the buccal branche of the facial nerve to form the buccal plexus. After this its termini branches are distributed to the skin over the buccinator muscle an

















THE HEAD AND NECK


i 3 Tl


mucous membrane which lines it. The buccal nerve furnishes ' branches, the lateral pterygoid and the anterior deep temporal ye. The nerve to the external pterygoid muscle leaves it near its [in, and enters the lateral pterygoid muscle on its deep surface.

anterior deep temporal nerve arises from it after it has passed

ween the two heads of the lateral pterygoid. These two branches e all the motor fibres from the buccal nerve, which after this is irelv sensory.

Posterior Trunk. —This division is larger than the anterior, and dmost entirely sensory, the only motor fibres which it contains ng destined for the mylo-hyoid branch of the inferior dental nerve, branches are three in number—namely, (i) auriculo-temporal, inferior dental, and (3) lingual.

Auriculo-temporal Nerve. —This nerve, which is sensory, arises two roots, between which the middle meningeal artery ascends the foramen spinosum. Then the two roots join, and the nerve is backwards deep to the lateral pterygoid muscle. Having passed se behind the mandibular joint to the interval between that joint 1 the auricle, it enters the upper part of the parotid gland. It

n changes its course and passes upwards, after which it crosses
zygoma and descends close behind the superficial temporal artery

end in its terminal temporal branches.

Branches of Communication. —(1) Each root of the auriculonporal nerve receives a small branch from the otic ganglion. These inches contain fibres of the glosso-pharyngeal nerve through (a) its npanic branch, ( b) the tympanic plexus, and (c) the lesser superficial trosal nerve, which latter is reinforced by a branch from the ganglion the facial nerve. These glosso-pharyngeal fibres are destined for 3 parotid gland. (2) Two communicating branches pass to the nal nerve in the parotid gland.

Branches of Distribution. —(1) Articular branches enter the temporomdibular joint through the back part of the capsule. (2) Glandular inches are distributed to the parotid gland, to which they conduct res of the glosso-pharyngeal nerve. (3) The branches to the ■ external ditory meatus , upper and lower, enter the meatus between its carti^inous and osseous parts, and supply the skin which lines it, the •per branch also giving twigs to the outer layer of the tympanic mibrane. (4) Auricular branches are distributed to tfife skin of e tragus and the upper part of the outer surface of the auricle. The stribution of the meatal and auricular branches explains why pain le to affections of the lower teeth may be referred to the ear canal id auricle. (5) The temporal branches are terminal. They accommy the branches of the superficial temporal artery, and supply the in of the temporal region as high as the vertex of the skull. They mmunicate with the temporal branches of the facial and the zygoatico-temporal nerve.

Inferior Dental Nerve. —This nerve, though chiefly sensory, conins motor fibres, which, however, leave it in its mylo-hyoid branch.



1312


A MANUAL OF ANATOMY


It passes downwards, being at first under cover of the lateral ptery^ muscle. After escaping from beneath that muscle, it descends u the spheno-mandibular ligament and medial pterygoid muscle to mandibular foramen, through which it passes into the mandibular ca after having parted with its mylo-hyoid branch. The lingual ne is anterior and medial to it, and the inferior dental artery is postei and lateral to it. Within the mandibular canal the nerve is accc panied by the inferior dental artery, and, having arrived at the le of the mental foramen, it terminates by dividing into two brand mental and incisive.

Branches. —(i) The mylo-hyoid nerve is given off from the par trunk just before it passes through the mandibular foramen, takes all the motor fibres from the parent trunk, and in comp£


Internal Carotid Artery with Sympathetic Plexuses Facial Nerve in Facial Canal


Maxillary Neive

Abducent Nerve . Internal Carotid Artery


Oculo-motor Nerve Optic Nerve


Chorda Tympani Glosso-pharyngeal f Inferior Dental

Accessory "~j~ Mylo-hyoid


Supra-orbital Nerve


_ Supratrochlear -- Frontal '* Infratrochlear Naso-ciliary Lacrimal (cut) Ophthalmic Infra-orbital


Spheno-palatine Ganj Anterior Superior De Middle Superior Deni

I Posterior Superior / Dental


Hypoglossal

Vagus


Otic Ganglion frA ' Lingual ') Submandibular Ganglion


Nerve to Thyro-hyoid Muscle

Fig. 794 .—General View of the Trigeminal Nerve (Hirschfeld ani

Leveille.


1, sterno-mastoid; 2, mylo-hyoid; 3, medial pterygoid.


with the mylo-hyoid branch of the inferior dental artery pierces f lower part of the spheno-mandibular ligament, and then passes dow wards and forwards in the mylo-hyoid groove of the mandible. T nerve and artery are maintained in position within this groove by expansion from the lower part of the spheno-mandibular ligamei which is attached to the lips of the groove. Then the nerve pass forwards on the inferior surface of the mylo-hyoid muscle unc cover of the superficial part of the submandibular gland. Havi furnished twigs to the mylo-hyoid muscle, it terminates in the anteri belly of the digastric.

(2) The dental branches arise from the parent trunk, whilst traverses the mandibular canal. They communicate with each oth to form a delicate plexus, from which branches are given off to t







THE HEAD AND NECK


  • 3*3


'S of the lower molar and premolar teeth, as well as to the adjacent of the gum. The pulp branches correspond in number to the s of the teeth, and each enters through a minute opening on the emity of the fang.

3) The mental nerve is one of the two terminal branches. It rges from the mandibular canal through the mental foramen, its distribution, see p. 1277.

4) the incisive branch is the termination of the inferior dental. >egins at the level of the mental foramen, and passes almost ar as the middle line. Its dental branches communicate in a iform manner, and supply the pulps of the lower canine and »or teeth, as well as the adjacent portion of the gum.


Naso-ciliary Nerve


Frontal Nerve Lacrimal Nerve Ciliary Ganglion \ Internal Carotid Artery

Ophthalmic Nerve Trigeminal Ganglion ter Superficial Petrosal Nerve

1 to Lesser Sup. Pet. N.

acial Nerve in Facial Canal

ior Auricular Nerve

Facial Nerve * /

/ I ' /

Internal Carotid Artery ' ] / / /

Chorda Tympani Nerve’ / < ‘

Mandibular Nerve / / /

Inferior Dental Nerve / j Otic Ganglion Lingual Nerve


Lacrimal Gland Ciliary Nerves


Branch of Oculo-motor Nerve to Inferior Oblique Maxillary Nerve Spheno-palatine Ganglion


Long Spheno-palatine Nerve


•Greater Palatine Nerve


Submandibular Ganglion Sublingual Ganglion


Fig. 795. —Scheme of the Trigeminal Nerve and its Ganglia

(Hirschfeld and Leveille.)


jingual Nerve. —This nerve is sensory. It descends deep to the ral pterygoid muscle, lying anterior and medial to the inferior

al nerve. Whilst under cover of that muscle it receives near its

in the chorda tympani nerve, which joins it from behind at an

e angle, in a direction downwards and forwards, after leaving

tympanic cavity through the anterior canaliculus for the chorda pani nerve. Below the lateral pterygoid muscle the lingual nerve

es downwards and forwards between the medial pterygoid muscle

the mandibular ramus, and over the mandibular fibres of the aior constrictor muscle. Below the level of the third lower molar h it lies immediately beneath the mucous membrane of the mouth, is here easily reached. It then crosses the stylo-glossus, and es forwards superficial to the hyo-glossus close to the side of the 'ue. Upon the latter muscle it describes a slight curve with the /■exity downwards. It then passes deep to the mylo-hyoid muscle,

83






1314


A MANUAL OF ANATOMY


where it lies above the deep part of the submandibular gland a the submandibular duct, and has the submandibular ganglion s pended from it. Finally, having looped under the submandibu duct from without inwards, it continues its course as far as the tip the tongue. As it passes along the side of the tongue the nerve immediately beneath the mucous membrane.

Branches of Communication. —(1) Chorda tympani (sensory facial); (2) two branches to the submandibular ganglion; and (3) ( or two filaments to the hypoglossal nerve at the anterior border the hyo-glossus muscle.

Branches of Distribution. —(1) Buccal , to the mucous membrs of the floor of the mouth and of the gums; (2) glandular , to the si


Tympanic Plexus

\ Facial Ganglion


Fig. 706.—Relations of the Petrous Part of the Internal Carotii

Artery.


lingual gland; and (3) lingual , to the mucous membrane of the si( and dorsum of the tongue over its anterior two-thirds. These lingi branches pierce the muscular tissue of the tongue, and are destir chiefly for the filiform and fungiform papillae.

Otic Ganglion. —The otic ganglion is a small oval body, of a pink: colour, which is situated close to the foramen ovale on the deep surfc of the mandibular nerve at the place of origin of the nerve to t internal pterygoid muscle, with which it is closely connected. It I the middle meningeal artery behind it, and the cartilaginous part the pharyngo-tympanic tube on its inner side. The ganglion I three roots. One root (motor-sensory) is derived from the nerve internal pterygoid (motor and probably sensory fibres). A seco root (sensory-motor) is represented by the lesser superficial petro:




THE HEAD AND NECK


1315


/e, which joins the back part of the ganglion. The sensory fibres Le from the glosso-pharyngeal by means of (1) the tympanic nerve, the t}/mpanic plexus, and (3) the lesser superficial petrosal. The or fibres conveyed by this root come from the ganglion of the facial /e through the branch which that ganglion gives to join the lesser grficial petrosal nerve. The third root (sympathetic) comes from sympathetic plexus around the middle meningeal artery.

Branches—(1) Of Communication.— (a) Two branches pass to the iculo-temporal nerve, one to each root. These carry secretory so-pharyngeal fibres which are destined for the parotid gland. A branch joins the chorda tympani. (c) A branch joins the nerve he pterygoid canal.

(2) Of Distribution. —Muscular branches are said to be given to tensor tympani and tensor palati, though the modern view is that ti these nerves are direct branches of the nerve to the internal -ygoid muscle.

Submandibular Ganglion (Submaxillary Ganglion). —This ganglion f small size, and is connected with the lingual nerve in the subidibular region. It is situated upon the upper part of the hyo;sus muscle, between the lingual nerve and the deep part of the mandibular gland, and under cover of the posterior part of the lo-hyoid muscle. It is suspended from the lingual nerve by two necting branches, posterior and anterior, which stand apart from h other. The posterior connecting branch, sometimes broken up ) two or three twigs, conveys sensory fibres from the chorda tympani isory portion of the facial) and lingual nerves, the latter being a nch of the mandibular nerve. The anterior connecting branch resents fibres passing from the ganglion to the lingual nerve.

The posterior branch consists of fibres which are derived from the rda tympani of the facial, and from the lingual nerve. 1 his terior branch may exist as two twigs. The anterior branch is an et from the ganglion to join the lingual. I he sympathetic root of ganglion is derived from the plexus on the cervical portion of the al artery.

Roots of the Submandibular Ganglion.

Secretory. Sensory. Sympathetic.

tn chorda tympani From lingual. From plexus on cervical portion

of facial. of facial artery.

The submandibular ganglion has three roots—secretory, sensory.. I sympathetic. The secretory root comes from the chorda tympani ve; the sensory root from the lingual nerve; and the sympathetic t from the plexus on the cervical portion of the facial artery. I he retory and sensory roots are the posterior connecting branch of the tglion.

Branches. —These proceed from the lower and anterior parts of ganglion, and are as follows: (1) glandular, to the submandibular ad; (2) branches to the submandibular duct; (3) buccal, to the


1316


A MANUAL OF ANATOMY


mucous membrane of the floor of the mouth; and (4) an anter connecting branch, which passes to the lingual nerve. The anter connecting branch probably consists of both chorda tympani a lingual fibres, and it accompanies the lingual nerve to the tongue, furnishes twigs to the sublingual gland, and a small ganglion associa with these twigs has been described under the name of the subling ganglion.

Summary of the Mandibular Nerve—1. Cutaneous Distribution. —It supp

(1) a portion of the dura mater, and the mucous membrane of the mast air-cells; (2) the skin over the greater part of the temporal region; (3) the s of the external auditory meatus, and the outer surface of the tympanic m( brane; (4) the skin of the tragus, and of the upper part of the outer surface the auricle; (5) the skin over the body of the mandible, including the skin the chin and lower lip, as well as the mucous membrane of the lower lip; (6) mucous membrane of the floor of the mouth, and the lower gum; and (7) sides and dorsum of the tongue over its anterior two-thirds. 2. Articular I tribution. —It supplies the mandibular joint. 3. Dental Distribution. —It s plies the pulps of all the lower teeth of one side, and the mucous membr; of the outer surface of the lower gum of one side. 4. Glandular Distribution.gives branches to the parotid, submandibular, and sublingual glands. 5. Mi cular Distribution. —It supplies (1) the muscles of mastication—namely, ■ masseter, temporal, lateral pterygoid, and medial pterygoid; (2) the mylo-hy and anterior belly of the digastric; and (3) the tensor palati and tensor tympc

The Mandibular Joint.

The mandibular joint belongs to the class of synovial joints, a to the subdivision of hinge joints. The articular surfaces are (1) t anterior part of the articular fossa in front of the squamo-tympai fissure, and (2) the head of the mandible.

Ligaments.— The capsular ligament consists of scattered fibr which form a thin loose investment to the joint on its anterior, medi and posterior aspects, being completed on the outer aspect by t temporo-mandibular ligament.

The temporo-mandibular ligament (external lateral ligament) is

short strong bundle of fibres, which is attached above to the tuber* of root of the zygoma, and below to the condylar tubercle and the out and back part of the neck of the mandible. Its fibres are direct obliquely downwards and backwards. This ligament forms the latei portion of the capsular ligament.

The spheno-mandibular ligament (long internal lateral ligament) a long flat band, which stands off from the joint, and therefore has : direct relation to it. It is somewhat triangular, being narrow abo and broad below. Superiorly it is attached to the spine of the sphenc bone, and interiorly to the lingula and the inner margin of the mandibul foramen. Its fibres are directed downwards and slightly forwarc The first part of the maxillary artery separates it from the neck the mandible; and inferiorly the inferior dental vessels and ner intervene between it and the ramus of the mandible. At its low attachment it is spread over the upper end of the mylo-hyoid groo\ and is here pierced by the mylo-hyoid nerve and artery. The maxilla


THE HEAD AND NECK


1317


ry and the auriculo-temporal nerve pass between the temporoldibular and spheno-mandibular ligaments.

rhe spheno-mandibular ligament is formed beside the skeletal bar of the visceral arch.


Capsular Ligament


Fig. 797.—The Mandibular Joint (Medial Aspect).


The stylo-mandibular ligament is a stout process of the deep cervical

ia, which extends from the styloid process of the temporal bone

tr its tip to the angle and adjacent portion of the posterior border


Articular Disc


Fig. 798.—The Mandibular Joint opened (Lateral Aspect).


the ramus of the mandible. Superiorly it gives origin to a few res of the stylo-glossus and interiorly it is implanted between the sseter and medial pterygoid muscles. It separates the subman>ular gland from the lower portion of the parotid gland.





1318


A MANUAL OF ANATOMY


The articular disc is an oval plate which is interposed between t] two articular surfaces. It is thinnest at the centre, where it is occ sionally perforated, and thickest posteriorly. Its superior surface concavo-convex from before backwards, in adaptation to the co vexity of the articular eminence and the concavity of the articul fossa. Its inferior surface is concave, and fits upon the head of ti mandible. Its circumference is connected with the capsular ligamer and anteriorly it gives partial insertion to the lateral pterygoid muse] It divides the joint into two compartments, upper and lower, whit are usually distinct.

The synovial membranes are two in number, upper and lower, oi being above and the other below the articular disc. The upper synovi membrane is larger and looser than the lower, and when the articul; disc is perforated at the centre, the two synovial cavities are continuoi through the perforation.

Arterial Supply .—The superficial temporal artery chiefly.

Nerve-supply .—The auriculo-temporal nerve and offsets from tl masseteric nerve.

Movements. —These are as follows: (1) depression, (2) elevation, (3) protra tion, (4) retraction, and (5) lateral movements. There being two divisions the joint, upper and lower, different movements occur in each. The movemei in the upper compartment is of a gliding character, whilst in the lower compartme it is of a hinge character. When the mandible is depressed, as in opening t] mouth, the head and the articular disc move forwards on to the articular eminent In cases of over-depression, as in violent yawning, or forcing too large a boc into the mouth, the head is apt to slip over the articular eminence into tl infratemporal fossa, and when this takes place dislocation of the mandible the result. The movement of forward gliding on the part of the head at articular disc during depression takes place in the upper compartment of tl joint. Another movement, however, of a hinge character is taking place in tl lower compartment of the joint between the head and the articular disc. This co sists in the head rotating on the under surface of the plate round a transverse axi

When the mandible is elevated, as in shutting the mouth, the changes whi< occur in both compartments of the joint are the reverse of those just describe as taking place in depression. The head and articular disc glide backwan into the articular fossa, and at the same time the head rotates back to its previoi position. In protraction, as when the lower incisors are protruded beyond tl upper, and in retraction, the movement mainly takes place in the upper cor partment of the joint, and consists in the head and the articular disc glidii forwards and backwards. When these movements are performed alternate on each side the lateral oblique movements, as in grinding or chewing, take plac and the head and the articular disc of one side move forwards and backward whilst the other head and the articular disc move in the opposite directio During these movements oblique rotation is taking place in the lower compar ment of the joint.

Muscles concerned in the Movements.—Depression is effected by the platysm mylo-hyoid, anterior belly of the digastric, and genio-hyoid muscles; and elev. tion by the anterior fibres of the temporal, masseter, and medial pterygo muscles. Protraction is produced by the lateral pterygoid, the superficial fibr of the masseter, and slightly by the medial pterygoid; and retraction by tl posterior fibres of the temporal and the deep fibres of the masseter. The grindil movement is effected by the lateral pterygoid muscles acting alternately. Tl axis of the movement in opening and closing the mouth passes through tl mandibular foramina.


THE HEAD AND NECK


1319


The Maxillary Nerve.


The maxillary nerve is the second division of the trigeminal nerve, 1 in size is intermediate between the mandibular and the ophthalmic, is entirely sensory, and arises from the trigeminal ganglion. Its irse is forwards to the foramen rotundum, by which it leaves the nial cavity. Then it enters the posterior part of the pterygoatine fossa, and crosses the upper part of that fossa to the inferior )itai fissure, through which it passes on to the floor of the orbit. It w takes the name of the infra-orbital nerve, and traverses the infra)ital groove, and then the infra-orbital canal, on the floor of the )it. Finally, it leaves this canal through the infra-orbital foramen der cover of the levator labii superioris, and ends in its terminal inches. The course of the maxillary nerve and its continuation, > infra-orbital nerve, is almost directly forwards, with a slight •lination outwards just before the orbit is entered.

Branches.— These are as follows:


In Infra-orbital Canal.

Middle superior dental. Anterior superior dental.


Intracranial.

Meningeal.


On the Face.

Palpebral.

Nasal.

Labial.


In the Pterygo-palatine Fossa.

Zygomatic.

Ganglionic.

Posterior superior dental.


The meningeal branch supplies the dura mater of the middle anial fossa.

The zygomatic nerve (temporo-malar nerve) is the first branch of e maxillary in the pterygo-palatine fossa. It arises from its uppei rface, and enters the orbit through the inferior orbital fissure. F01

further course, see p. 1259.

The ganglionic branches (spheno-palatine nerves) are two in number, ley arise from the lower aspect of the parent trunk, and, aftei a

ry short descending course, they end for the most part in the sphenoilatine ganglion, to which they convey sensory fibres, and of which

ey are the sensory roots. Man} 7 of their fibres, howevei, pass cleai the grey matter of the ganglion, and are prolonged into the nasal

id palatine branches of the ganglion.

The posterior superior dental branches arise from the maxillaiy as is about to pass through the inferior orbital fissure. They are mally two in number, but sometimes they arise by a single trunk, hey descend in grooves on the posterior surface of the maxilla in impany with branches of the posterior superior dental artery, and ve off branches to the gum and contiguous parts of the mucous membrane of the cheek. Then they traverse the posterior denta inals, and within the substance of the bone communicate with each filer and with the middle superior dental nerve to form a delicate exus, from which branches are given^off to the pulps ot the thiee


!32o A MANUAL OF ANATOMY

upper molar teeth. Slender filaments are also furnished to the mucc membrane lining the maxillary sinus.

The middle superior dental branch arises from the main trunk it lies in the infra-orbital groove near the inferior orbital fissure, descends in the middle dental canal of the maxilla. Its brand communicate with each other, and with the posterior superior a anterior superior dental branches within the substance of the boi to form a delicate plexus, from which branches are given to the pu] of the upper two premolar teeth and to the gum. This nerve a' furnishes delicate filaments to the mucous membrane lining t maxillary sinus. Two enlargements are described in connection wi the middle superior dental branch. One is situated at its communk tion with the posterior superior dental branch, and is known as t ganglion 0} T alentin ; and the other at its communication with t anterior superior dental, this one being known as the ganglion Bochdalek. 86

The anterior superior dental branch arises from the infra-orbil

nerve near the front part of the infra-orbital canal, and descends, company with the anterior superior dental artery, in the anterior deni canal. Its branches communicate with each other, and with the midc superior dental branch, to form a delicate plexus, from which branch are given to the pulps of the upper canine and incisor teeth. Tt nerve also furnishes delicate filaments to the mucous membrane linii the maxillary sinus, and a nasal branch, which enters the nasal cavi and supplies the mucous membrane of the anterior part of the infer! meatus and adjacent portion of the inferior nasal concha.

The facial branches of the infra-orbital nerve—palpebral, nas£ and labial—have been already described (see p. 1276).

It is to be noted that there are three superior dental branche the posterior being a branch of the maxillary, and the middle and anteri being branches of the infra-orbital; whilst there is onlv one infer! dental nerve, which is a branch of the mandibular.

Spheno-palatine Ganglion (Meckel’s Ganglion). —It is a sms triangular, somewhat reddish body, situated in the upper part of tl pterygo-palatine fossa close to the spheno-palatine foramen, whic leads through the inner wall of the fossa to the superior meatus of tl nasal cavity. It is suspended from the maxillary nerve by some < the fibres of the two ganglionic branches of that nerve, many fibr< of these two branches passing clear of the grey matter of the ganglic into its nasal and palatine branches. The fibres conveved to tl grey matter of the ganglion by the two ganglionic branches represer its sensory root or roots.

The ganglion has sensory and sympathetic roots, but no mote root. The sensory roots are derived from two sources—maxillary an facial. The maxillary sensory root-fibres form two bundles, an represent portions of the two ganglionic branches, by which the ganglio is suspended from the trunk of the maxillary nerve in the pterygc palatine fossa. The facial sensory root-fibres are represented by tb


THE HEAD AND NECK


1321


iter superficial petrosal nerve , which is a branch of the ganglion the facial nerve. The sympathetic root is formed by the deep vsal nerve from the carotid plexus of the sympathetic.

The facial sensory root (greater superficial petrosal) and the svmhetic root (deep petrosal) join to form the nerve of the pterygoid al in the foramen lacerum. After traversing the pterygoid canal n behind forwards, the nerve enters the pterygo-palatine fossa l joins the back part of the spheno-palatine ganglion. In the rygoid canal the nerve gives off one or two nasal branches, which lS through the floor of the canal, and are distributed to the mucous mbrane of the posterior part of the roof of the nasal cavity and acent part of the septum.


Short Spheno-palatine Nerves Ganglionic Branches from Maxillary Olfactory Filaments j i Nerve of Pterygoid Canal


Nasal Branches


i. 799. —Nerves of the Nasal Cavity, and the Spheno-palatine Ganglion, with its Branches (Medial Aspect) (Hirschfeld and Leveill£).


Branches of the Spheno-palatine Ganglion. —These are arranged in ir sets:


iscending.

Orbital.


Posterior.

Pharyngeal. Nerve of pterygoid canal.


Medial.

Short sphenopalatine. Long sphenopalatine.


Descending.

Greater palatine. Lesser palatine.


Ascending Branches.—Orbital branches are two or three in number, d enter the orbit through the inferior orbital fissure to be distributed the periosteum. Thev have been described by Luschka as sending iments through the inner wall of the orbit to supply the mucous mbrane of the posterior ethmoidal and sphenoidal sinuses.

Posterior branches are the pharyngeal nerve and the nerve of the irygoid canal. The pharyngeal nerve passes backwards in the




I 3 22


A MANUAL OF ANATOMY


palatovaginal canal along with the pharyngeal branch of the maxillai artery, and is distributed to the mucous membrane of the upp< part of the pharynx in the region of the orifice of the pharyngi tympanic tube.

Medial branches are the long and short spheno-palatine nerve The short spheno-palatine nerves (superior nasal nerves) are of sma

size, and derive some of their fibres from the ganglionic branches < the maxillary nerve. They are about six in number, and, springir from the inner part of the ganglion, they enter the superior meatus < the nose through the spheno-palatine foramen. They supply tl mucous membrane of the superior and middle conchae, the superb meatus, the posterior ethmoidal sinus, the middle meatus, and tl upper and back part of the septum.

The long spheno-palatine nerve (naso-palatine nerve) enters tl nasal cavity along with the short spheno-palatine nerves. It cross< the roof of the cavity, and then passes downwards and forwards upc the septum, lying in the groove on the lateral surface of the vome Having arrived at the incisor crest, the left long spheno-palatir nerve descends through the anterior incisive canal, and the rigl descends through the posterior. Having reached the incisive fos< in this manner, the two nerves communicate in a plexiform manne and delicate filaments are furnished to the mucous membrane of tl hard palate behind the incisor teeth. In this situation communic; tions are established with the greater palatine nerve of each sid< As the long spheno-palatine nerve traverses the groove on the later; surface of the vomer, it furnishes twigs to the mucous membrane < the nasal septum, and in this part of its course it is accompanied b the posterior septal branch of the spheno-palatine artery; but th artery does not accompany it through the median incisive canal.

Descending branches are the greater and lesser palatine nerve They arise from the lower part of the ganglion, usually by a commo trunk, and they derive some of their fibres from the ganglionic branch* of the maxillary nerve.

The greater palatine nerve descends in the greater palatine cana and escapes from it through the greater palatine foramen. Then divides into branches which pass forwards and inwards, occupyin grooves on the hard palate, to the mucous membrane and glands ( which, as well as to the mucous membrane of the upper gum on it inner aspect, they are distributed. In the region of the incisive foss this nerve communicates with the long spheno-palatine nerve. A it descends in the greater palatine canal it furnishes nasal branche which enter the nasal cavit}/, and are distributed to the mucoi membrane over the inferior concha,, except anteriorly, and to that < the adjacent portion of the inferior meatus. The lesser palatine nerv< descend in the lesser palatine canal, after emerging from which the are distributed to the mucous membrane of the soft palate and tonsi They have been said to furnish branches to the levator palati an musculus uvulae, the fibres of these branches being derived from tl



THE HEAD AND NECK


i 3 2 3


liculate ganglion of the facial through the great superficial petrosal, ich contributes to the formation of the nerve of the pterysoid canal, i conveys motor fibres to the ganglion. The two muscles in question, wever, are supplied by the bulbar part of the accessory nerve through

pharyngeal plexus.

Summary of the Maxillary Nerve and the Spheno-palatine Ganglion.—1. Cuteous Distribution. —(1) The skin of the anterior part of the temporal region, I over the zygomatic bone; (2) the skin from the lower eyelid down to the per lip, including the skin of the side of the nose; (3) the mucous membrane the naso-pharynx in the vicinity of the orifice of the pharyngo-tympanic; the mucous membrane of the nasal cavity; (5) the mucous membrane of the xillary sinus; (6) the mucous membrane of the soft palate and tonsil; and the mucous membrane of the hard palate, with its glands, and that of the ler surface of the upper gum. 2. Dental Distribution. —The pulps of all the per teeth of one side, as well as the mucous membrane of the outer surface of j upper gum.

In addition to the foregoing, the maxillary nerve supplies the periosteum of ? orbit, and the dura mater of the middle cranial fossa.


Deep Dissection of the Neck.

Stylo-pharyngeus — Origin .—The base of the styloid process of the mporal bone on its inner aspect.

Insertion. —(1) The posterior border of the lamina of the thyroid rtilage, and (2) the lateral wall of the pharynx, its fibres blending th those of the palato- g-fv. process







1324


A MANUAL OF ANATOMY


bone, and, after traversing this canal, it enters the cranial cavit The vessel is divided into three parts—cervical, petrous, and cavernoi

The Cervical Part. —This part of the vessel extends from the level the upper border of the thyroid cartilage to the carotid canal on t inferior surface of the petrous part of the temporal bone. Its com is upwards, and at first it lies in the carotid triangle, where it is plac lateral to and behind the external carotid artery.

Relations — Superficial .—This part of the vessel is comparative superficial, being covered by the integument,, platysma, and sterr mastoid, the latter overlapping it. After leaving the carotid trian^ the artery becomes deeply placed, and passes deep to the posteri belly of the digastric and stylo-hyoid muscles, parotid gland, style process, and stylo-pharyngeus muscle. In this part of its com the vessel is crossed by the hypoglossal, accessory, and glosso-phary geal nerves, and the pharyngeal branch of the vagus, and by t occipital and posterior auricular arteries. The relation of the arte to the external carotid here undergoes a change. The level where t change takes place is as the internal carotid passes deep to the stylo process of the temporal bone, and the change consists in the extern carotid taking up a position directly anterior to the internal caroti I he two arteries are, however, separated from each other by the folio 1 ing structures: (i) the styloid process or stylo-hyoid ligament; (2) t' stylo-pharyngeus muscle; (3) the glosso-pharyngeal nerve; (4) t' pharyngeal branch of the vagus; and (5) the parotid gland.

Posterior .—The longus capitis, the superior cervical ganglion the sympathetic, and the superior laryngeal branch of the vagus.

Lateral .—The internal jugular vein and vagus nerve, the ner being on a plane posterior to both artery and vein. These thr structures are still surrounded by a sheath which is an upward e tension of the carotid sheath previously described. Close to t. base of the skull the glosso-pharyngeal, accessory, and hrypogloss nerves lie between the internal artery and the internal jugular vei The glosso-pharyngeal nerve soon passes forwards superficial to t. artery, the accessory nerve passes backwards superficial to the vei and the hypoglossal nerve passes forwards superficial to the arte at the lower border of the posterior belly of the digastric muscle.

Medial .—The ascending pharyngeal artery, the lateral wall the pharynx, the tonsil, and the superior laryngeal nerve.

Development. —The internal carotid artery is developed from the thi aortic arch and the part of the dorsal aorta in front of this arch.

The Glosso-pharyngeal Nerve.

The glosso-pharyngeal or ninth cranial nerve is a mixed nerv consisting of both afferent or sensory and efferent or motor fibre It leaves the cranial cavity through the middle compartment of t] jugular foramen, along with the vagus and accessory nerves, bi enclosed in a separate sheath of the dura mater, and lying anteri


THE HEAD AND NECK


1325


these two nerves. In passing through the jugular foramen the ve has two ganglia, the upper one, which is small and situated the upper part of the foramen, being called the superior ganglion yular ganglion) ; and the lower one, which is rather larger, being ied the inferior ganglion {petrous ganglion). The latter is about ich in length, and lies in the lower part of the foramen, where it upies a groove on the petrous portion of temporal bone. After leaving the jugular mien, the nerve at first descends between internal carotid artery and internal jugular n, being lateral to the vagus nerve. It n passes downwards and forwards in front the internal carotid artery, and under r er of the styloid process, stylo-pharyngeus scle, and external carotid artery. It next ves round the hinder border of the styloiryngeus, and crosses it (Fig. 800) superally in a forward direction. Finally, it

ses deep to the hyo-glossus muscle, and

reaches the posterior third of the tongue, ere it divides into its terminal branches.

The superior ganglion (jugular ganglion), as ted, is very small, and involves only a few the fibres of the nerve, the other fibres >sing clear of, but close to, the ganglion,

I being continued into the nerve beyond it. is ganglion neither gives nor receives any branches, and is someles absent.

The inferior ganglion (petrous ganglion), unlike the jugular, Fives all the fibres of the nerve, and it furnishes connecting branches I the tympanic nerve.

Branches of the Glosso-pharyngeal Nerve—1. From the Inferior Qglion — (a) Branches of Communication .—One to the superior cervical lglion of the sympathetic; one to the auricular branch of the superior lglion of the vagus; and one to the superior of the vagus.

(b) Branch of Distribution. —This is called the tympanic nerve rve of Jacobson). After leaving the inferior ganglion it ascends, company with the tympanic branch of the ascending pharyngeal ery, through the canaliculus for the tympanic nerve. In this y it enters the tympanic cavity at the junction of the inner wall and ir, and ascends upon the inner wall. Being joined by the caroticonpanic branch of the carotid plexus of the sympathetic, it breaks into branches which occupy grooves upon the promontory and m the tympanic plexus. From this plexus the tympanic nerve erges under the name of the lesser superficial petrosal nerve, which ves the tympanic cavity and traverses a minute canal in the petrous tie, passing in its course beneath the upper portion of the canal ich lodges the tensor tympani muscle. Whilst in this canal it is


Fig. 801.—Sketch showing the Relations between Ninth, Tenth, Eleventh, and Twelfth Nerves, in Carotid Sheath just below Skull.



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A MANUAL OF ANATOMY


Auriculo temporal Nerve Facial Nerve j Posterior Auricular Nerve •, .


Glosso-pharyngeal Nerve Accessory Nerve .


Greater Occipital Nerve Hypoglossal Nerve


Sup. Cervical Symp. Ganglion — External Carotid Artery Internal Carotid Artery Sympathetic Trunk.

Com. Car. Art. and'Symp. Plexus — V|j Phrenic Nerve -jM I


Right Ansa Subclavia


First Thoracic Ganglion


Right Posterior-;

Pulmonary Plexus


Vena Azygos Vascular Branch


Intercostal Vessels ( and Nerve 1 r


Ramus Communicans Sympathetic Trunk


Lesser Splanchnic Nerve—Greater Splanchnic Nerve Lowest Splanchnic Nerve.'


SL _

W m Hypoglossal Nerve

vZffl _ Superior Laryngeal Nerve

yriff-T . Vagus Nerve

- Middle Cervical Sympathetic

Ganglion

••jS-imv _ Recurrent Laryngeal Nerve

_Cardiac Branches of Vagus

_ Phrenic Nerve

Timex -- ’

rfii


_ Root of Right Lung


.. Right Vagus Nerve on CEsophagus


CEsophageal Plexus


Liver (cut)

Left Vagus Nerve


A.Descending Aorta Thoracic Duct


\ Branches of Vagus I on Stomach


Right Coeliac Ganglion "Coeliac Plexus


'•'Superior Mesenteric Artery and Plexus


Renal Artery and Plexus Abdominal Aorta

S.V.C. Superior Vena Cava


I’ig. 802.—Nerves of the Right Side of the Face, Neck, and Thorax

(HlRSCHFELD AND LeVEILLEI.


















THE HEAD AND NECK


1327


Led by a communicating branch from the ganglion of the facial ve. It leaves the canal through the hiatus for the lesser superil petrosal nerve on the surface of the petrous bone, and then ses forwards and inwards beneath the dura mater. After this asses through the canaliculus innominatus, when present, or through fissure between the petrous temporal and greater wings of the Lenoid, or sometimes through the foramen ovale, into the infraiporal fossa, where it joins the otic ganglion, to which it conducts sso-pharyngeal and facial fibres.

2. From the Trunk of the Nerve. —(1) A communicating branch netimes passes from the nerve a little below the inferior ganglion join the digastric branch of the facial nerve. (2) A carotid branch ises to the sympathetic plexus on the internal carotid artery. Pharyngeal Branches. —These are about four in number. Three of im unite, over the middle constrictor of the pharynx, with the subnsions of the pharyngeal branch of the vagus, and with branches the superior cervical ganglion of the sympathetic, to form the aryngeal plexus. The other pharyngeal branch pierces the superior istrictor, and is distributed to the mucous membrane of the upper rt of the pharynx. (4) A muscular branch to the stylo-pharyngeus iscle, some of the fibres of which pierce the muscle to supply the icous membrane of the pharynx. (5) Tonsillar branches form a cular plexus round the tonsil, known as the circulus tonsillaris; >m it branches supply the tonsil and region of the oro-pharyngeal hmus. (6) Lingual Branches. —Under cover of the hyo-glossus iscle, the terminal part of the nerve divides into two branches, rsal and lateral. The dorsal branch passes to the vallate papillae d the mucous membrane over the posterior third of the tongue, tending as far back as the front of the epiglottis. The lateral branch distributed to the mucous membrane of the side of the tongue r er about its posterior half.

Summary of the Glosso-pharyngeal Nerve— i- Cutaneous Distribution.— It

pplies (a) the mucous membrane of the tympanic cavity, the posterior third the tongue, the region of the oro-pharyngeal isthmus, and the pharynx, and the tonsil. 2. Muscular Distribution.— The stylo-pharyngeus. 3. Glandular stribution.— Through (1) its tympanic, subsequently lesser superficial petrosal, anch, (2) the otic ganglion, and (3) the auriculo-temporal neive, it furnishes

retory branches to the parotid gland.

The Vagus Nerve in the Neck.

The vagus, or tenth cranial, is a mixed nerve, consisting of both ferent and efferent fibres. It leaves the cranial cavity through the iddle compartment of the jugular foramen, being enclosed m the .me sheath of dura mater as the accessory, and, with that nerve, ing posterior to the glosso-pharyngeal. In the foramen it presents small enlargement called the superior ganglion. ATter emerging from le foramen it is joined by the cranial root of the accessory nerve, id here there is another enlargement, called the inferior ganglion.


1328


A MANUAL OF ANATOMY


This ganglion is larger and longer than the superior ganglion, full j inch in length, and presenting a somewhat plexiform appearana In this part of its course the nerve lies between the internal caroti artery and the internal jugular vein, the glosso-pharyngeal nerve bein in front of it and the accessory behind it. The hypoglossal'nerv lies at first deeply behind it, but subsequently turns round the oute side of the inferior ganglion. The vagus then descends within th carotid sheath, lying at first between the internal carotid artery an the internal jugular vein, and then between the common carotid arter and the internal jugular vein, being on a plane posterior to both vessels Within the sheath the nerve occupies a special compartment, situate in the back part of the septum which separates the artery from th vein. Below the root of the neck the right and left nerves have impor tant differences in their course and relations.

Branches —A. The Superior Ganglion (Ganglion of the Root)1. Branches of Communication. — (a) It receives two filaments from th cranial root of the accessory nerve. ( b) It communicates by a smal twig with the inferior ganglion of the glosso-pharyngeal nerve. ( c ) I communicates with the facial, and with the posterior auricular brand of the facial, through its auricular branch of distribution, (d) I receives a twig from the superior cervical ganglion of the sym pathetic.

2. Branches of Distribution. — (a) The meningeal branch takes c recurrent course, and, after entering the cranial cavity, supplies th< dura mater which lines the cerebellar fossa of the occipital bone ( b ) The auricular branch is of small size, and is soon reinforced by a twi£ from the inferior ganglion of the glosso-pharyngeal. It enters th( mastoid canaliculus through an aperture on the outer wall of th( jugular fossa. In this canaliculus it traverses the petrous portion 0: the temporal bone, crossing in its course the inner aspect of the descending portion of the facial canal a little above the stylo-mastoic foramen, where it forms its first communication with the facial nerve It then leaves the petrous temporal through the tympano-mastoic fissure, between the mastoid process and the tympanic plate, and then divides into two branches. One of these joins the posterioi auricular branch of the facial nerve, and the other is distributed tc (1 a ) the skin of the inner surface of the auricle, and (b) the skin of the lower and back part of the external auditory meatus.

B. The Inferior Ganglion (Ganglion of the Trunk)— 1. Branches of Communication. — (a) The most important branch of communication is the cranial root of the accessory nerve , which passes over the surface of the ganglion in intimate contact with it. Most of the cranial fibres are continued into the pharyngeal and superior laryngeal nerves, but some of them descend in the main trunk of the vagus, and pass into its cardiac and inferior laryngeal branches. The cranial fibres are to be regarded as of two kinds—namely, motor , for the muscles of the soft palate, pharynx, and larynx; and cardiac inhibitory, (b) Branches pass between the inferior ganglion and the hypoglossal nerve, (c) A


THE HEAD AND NECK


1329


municating branch is received from the superior cervical ganglion le sympathetic.

Branches of Distribution.—These are pharyngeal and superior ngeal.

fhe pharyngeal branch arises from the upper part of the inferior jlion, its fibres being chiefly derived from the cranial root of the ssory nerve. It passes forwards and downwards between the rnal and external carotid arteries, and divides into branches opposite middle constrictor muscle, which join the pharyngeal branches of ^losso-pharyngeal and superior cervical ganglion of the sympathetic )rm the pharyngeal plexus.

rhe pharyngeal plexus is situated upon the middle constrictor cle opposite the greater horn of the hyoid bone. It is formed by

he pharyngeal branch of the inferior ganglion of the vagus, derived

inally from the accessory; (2) the pharyngeal branches of the glossoryngeal; and (3) the pharyngeal branches of the superior cervical ^lion of the sympathetic.

Branches are distributed to (1) the constrictor muscles of the phai ynx, the mucous membrane of the pharynx; and (3) the palato-glossus, ito-pharyngeus, levator palati, and musculus uvulae. In this way the muscles of the soft palate except the tensor palati are supplied the accessory nerve. Branches of communication pass between plexus and the superior laryngeal and external laryngeal nerves, another branch, known as the lingual bvanch of the vagus, passes

he hypoglossal nerve. .

Superior Laryngeal Nerve.—This nerve, which is principally sensory,

es from the inferior ganglion of the vagus near its centre, and contains

es of the cranial root of the accessory nerve. It passes downwaids 1 forwards behind the internal carotid artery, having received comnicating branches from the superior cervical ganglion of the symhetic and from the pharyngeal plexus. As it passes behind the mnal carotid artery it divides into two branches, internal and externa . 5 internal laryngeal nerve, which is sensory, passes forwards, m npany with the superior laryngeal branch of the superioi thyroi ery, to the thyro-hyoid membrane, which it pierces under cover of

posterior border of the thyro-hyoid muscle. Having reached the

erior of the larynx, it divides into branches which supply the mucous mbrane of the epiglottis with its folds, a little of the back of the igue, the mucous membrane of the larynx as low as the vocal to ds, I that covering the lateral and posterior portions of the cricoid cartie. One branch descends over the inner surface of the lamina °f the /roid cartilage, and joins a branch of the lecunent aiyngea . e

ernal laryngeal nerve, of small size, descends deep o e s emo

^roid muscle to the crico-thyroid muscle, which it supplies. It 'nishes some twigs to the inferior constrictor, and a amen w ic \ ns the superior cardiac branch of the sympathetic. rec ? 1 ., s communicating branch from the supeiior ceivica gang ion o c

npathetic, and one or two branches from the pharyngea p exus.

84


1330


A MANUAL OF ANATOMY


Recurrent Laryngeal Nerve. —This nerve is mainly motor, and the principal motor nerve of the intrinsic muscles of the larynx, contains fibres of the cranial root of the accessory nerve. The ri{ nerve arises from the vagus at the root of the neck in front of t hrst. part of the subclavian artery, round the lower border of which bends, and then ascends behind it. Then it passes upwards ai inwards behind the carotid sheath and inferior thyroid artery to t groove between the trachea and the oesophagus. The left nerve aris in the thorax from the vagus in front of the arch of the aorta on a le\ with its lower border. It passes backwards below the arch and to t left of the ligamentum arteriosum, and then it turns upwards behii the arch. Having reached the groove between the trachea and t' oesophagus, it ascends therein to the neck. The right and left nerv pass upwards in the groove between the trachea and the cesophag on each side, lying usually behind the corresponding inferior thyro artery and in close relation with the lobes of the thyroid gland, i the level of the cricoid cartilage each nerve passes beneath the low border of the inferior constrictor muscle, and enters the larynx behii the crico-thyroid joint.

Extralaryngeal Branches. —(i) Communicating twigs pass betwe< the recurrent laryngeal nerve and the inferior cervical ganglion of tl sympathetic; (2) cardiac branches, which contain cranial fibres fro the accessory, are furnished to the deep cardiac plexus; (3) trache and oesophageal branches are supplied to these tubes; and (4) muscul offsets pass to the lower part of the inferior constrictor.

Intralaryngeal Branches. —These are chiefly muscular, and supp the intrinsic muscles of the larynx, except the crico-thyroid, whi( is supplied by the external laryngeal nerve. Sensory branches, howeve are given to the laryngeal mucous membrane below the vocal fold except over the lateral and posterior portions of the cricoid cartilag Within the larynx the nerve communicates with a branch of tl internal laryngeal nerve under cover of the lower part of the lamir of the thyroid cartilage.

For the explanation of the recurrent course of each recurrei laryngeal nerve, see p. 1121.

Cardiac Branches. —These are subject to variation as regan numbers. As a rule there are two, upper and lower, both of whic contain cranial fibres from the accessory. Those of the right sic pass behind the first part of the subclavian artery, and end in tl deep cardiac plexus. On the left side the upper nerve passes to tl deep cardiac plexus, but the lower nerve ends in the superficial cardie plexus.

Summary of the Vagus Nerve in the Neck— 1. Motor Distribution. —(1) Tl

muscles of the soft palate by accessory fibres, except the tensor palati; (2) tl constrictor muscles of the pharynx; (3) the intrinsic muscles of the larynx; ar (4) the muscular tissue of the oesophagus and trachea. 2. Sensory Distribution.It supplies (1) the pharynx, oesophagus, and trachea; (2) a limited portion of.tl dura mater; and (3) a small portion of the skin on the inner surface of the auricl as well as of the lower and back part of the external auditory meatus. 3. Con


THE HEAD AND NECK


I 33 I


.cations. —Each vagus nerve forms connections with the facial, glossoyngeal, accessory, hypoglossal, and sympathetic nerves. It is also con:d with the loop between the first and second cervical spinal nerves. Its important connection is that which is established with the cranial root of icessory nerve. The bulbar fibres of the nerve are probably chiefly conid in the innervation of the muscles of the soft palate (except the tensor

i), pharynx, and larynx, but also to a certain extent in the innervation of

leart.


Accessory Nerve.

fhe accessory or eleventh cranial nerve consists of two roots— ial and spinal. In the jugular foramen these two parts either e to form one trunk or freely intermingle, and a communication stablished between the cranial root and the superior ganglion of vagus by means of two twigs. The nerve passes through the liar foramen, being enclosed he same sheath of dura mater he vagus, behind which it lies, lediately beneath the jugular men the two parts of the nerve irate from each other, rhe cranial root passes over, in intimate contact with, the rior ganglion of the vagus, its fibres are continued partly • the pharyngeal and superior ngeal branches of the inferior glion, and partly into the lk of the vagus below the glion. These latter fibres are mately prolonged into the iiac and recurrent laryngeal riches of the nerve. The lial fibres of the accessor}/ regarded as (i) the motor nerves of (a) the muscles of the soft ite, except the tensor palati, (b) the constrictor muscles of the ,rynx, and (c) the intrinsic muscles of the larynx; and (2) the ibitory fibres of the heart.

The spinal root of the accessory nerve passes backwards and downds either behind or in front of the internal jugular vein. It then

  • ces the deep surface of the sterno-mastoid, which it supplies along

h a branch of the second cervical nerve. Then it crosses the terior triangle of the neck obliquely downwards and backwards to anterior border of the trapezius, beneath which it passes, supplying muscle, in company with branches from the third and fourth rical nerves.

Summary. —The spinal root of the accessory nerve supplies the trapezius and sterno-mastoid. The cranial root, through its connection with the vagus /e and its branches, supplies (1) the muscles of the soft palate, except the


Fig. 803. —Showing Relations between Accessory Nerve, Hypoglossal Nerve, and Occipital Artery a little below Skull Base.


1332


A MANUAL OF ANATOMY


tensor palati; (2) the constrictor muscles of the pharynx; and (3) the intrin muscles of the larynx. It also furnishes the inhibitory fibres of the heart, wh: reach that organ through the cardiac branches of the vagus.


Hypoglossal Nerve.


The hypoglossal or twelfth cranial nerve consists at first of b bundles, which pierce the dura mater separately. In passing throu the anterior condylar canal these two bundles unite to form one trur After leaving that canal the nerve lies deeply under cover of the interr carotid artery and internal jugular vein. It then turns round t outer side of the inferior ganglion of the vagus, with which it is close connected, and passes forwards between the internal carotid arte and internal jugular vein. Then it descends to the lower border the posterior belly of the digastric, at which level it hooks round t occipital artery from without inwards, and crosses in front of t external carotid artery and its lingual branch. In this part of i course the nerve lies in the superior carotid triangle. It next ru forwards above the hyoid bone, passing deep to the tendon of f digastric and the lower part of the stylo-hyoid muscle, and superfici to the hyo-glossus. After this it disappears deep to the mylo-hyoi still resting upon the hyo-glossus, where it is accompanied by tl vena comitans hypoglossi, and is covered by the deep part of t] submandibular gland. At the anterior border of the hyo-glossus is connected with the lingual nerve, and then enters the genio-glossr

Branches —1. Of Communication. —After leaving the anterior co dylar canal, the hypoglossal nerve .communicates with the infer! ganglion of the vagus. It then receives a branch from the super! cervical ganglion of the sympathetic, and one from the first cervic nerve, or the loop between the first and second. As it hooks rour the occipital artery it receives the lingual branch of the vagus fro the pharyngeal plexus; and at the anterior border of the hyo-glossi it is connected with the lingual nerve.

2. Of Distribution. —One or two meningeal branches arise from tl nerve in the anterior condylar canal, which take a recurrent cours and enter the cranial cavity to supply the dura mater near the canal

The ramus descendens hypoglossi nerve has been already describe (see p. 1205).

The nerve to thyro-hyoid will be found described on p. 1206.

The muscular branches are given off from the nerve as it lies upo the hyo-glossus under cover of the mylo-hyoid. These supply tl stylo-glossus, hyo-glossus, genio-glossus, and genio-hyoid. The nen to the genio-hyoid is composed of spinal fibres derived from the fin and second cervical nerves.

Ihe terminal branches pierce the under surface of the tongue, an are distributed to its muscular tissue.

The hypoglossal nerve receives many spinal fibres. Those derive from the first cervical nerve, or the loop between the first and seconc soon become applied to it, and most of them pass off to form the ramr


THE HEAD AND NECK


1333


endens hypoglossi. A few of these, however, still pass along the

n trunk. The spinal fibres derived from the second and third deal nerves in part ascend in the ramus descendens hypoglossi,

. then pass off from it to be applied to the main trunk in its onward rse.

Summary.—1. Distribution. —The hypoglossal fibres of the nerve supply stvlo-glossus, hyo-glossus, genio-glossus, and intrinsic muscles of the tongue, spinal fibres supply both bellies of the omo-hyoid, the sterno-hyoid, sternoroid, thyfo-hyoid, and genio-hyoid muscles. The hypoglossal nerve also plies the dura mater near the anterior condylar canal. 2. Connections. —-It blishes connections with (1) the inferior ganglion of the vagus; (2) the superior deal ganglion of the sympathetic; (3) the first two cervical nerves; (4) the ryngeal plexus, through the lingual branch of the vagus; and (5) the lingual /e from the mandibular division of the trigeminal nerve.

The Sympathetic Trunk.

Cervical Portion.—-This portion of the sympathetic trunk extends m the base of the skull, at the carotid canal on the under surface the petrous part of the temporal bone, to the root of the neck, ere it enters the thorax, passing on the right side behind the subvian artery. It lies directly behind the carotid sheath, and in nt of the transverse processes of the cervical vertebrae, resting upon

longus capitis and longus cervicis muscles. The cord presents

ee ganglia—superior, middle, and inferior.

Superior Cervical Ganglion.—This ganglion is fusiform and more in an inch long. It represents four ganglia united into one, and 'responding to the first four cervical nerves. It is situated in front the transverse processes of the second and third cervical vertebrae, d lies upon the longus capitis, the vagus nerve being lateral to it. either end it tapers, being continued superiorly into its ascending inch, and inferiorly into the descending trunk.

Branches.—-These may be conveniently arranged into internal rotid, lateral, medial.

The internal carotid nerve enters the carotid canal in the petrous rt of the temporal bone in company with the internal carotid artery, d divides into two parts. The lateral branch lies upon the outer le of the artery, and its subdivisions form by their interlacement the

ernal carotid plexus. From this plexus several communicating

anches are given off. (1) The carotico-tympanic nerve enters the mpanic cavity, and joins the tympanic branch of the glosso-pharynal, to take part in the tympanic plexus. (2) I he deep petrosal rve joins the greater superficial petrosal from the ganglion of the cial nerve in the upper part of the foramen lacerum, to form the rve of the pterygoid canal, which passes through the latter to join e spheno-palatine ganglion. (3) A branch (or branches) passes to in the abducent nerve. (4) One or more branches pass to join the Lgeminal ganglion. The internal carotid plexus furnishes filaments the coats of the internal carotid artery, and it receives a branch 3 m the tympanic plexus.


1334


A MANUAL OF ANATOMY


The medial branch of the internal carotid nerve lies upon the ini side of the internal carotid artery, to which it furnishes twigs, and subdivisions form by their interlacement the medial part of the inter] carotid plexus (cavernous plexus). This plexus lies in contact with 1 internal carotid artery as it traverses the cavernous sinus. Its co municating branches pass to join the oculo-motor, trochlear, a ophthalmic nerves, and the ciliary ganglion. The last-named brar forms the sympathetic root of the ciliary ganglion, and enters the or through the superior orbital fissure. It is the source of the motor sup] of the dilator pupillse muscle. The medial part of the internal caro plexus furnishes filaments to the coats of the internal carotid artei and offsets which accompany the branches of that artery, around whi they are disposed as plexuses.

The lateral branches are communicating, and pass to (i) each the upper four cervical nerves; (2) the inferior ganglion of the gloss pharyngeal; (3) the superior ganglion of the vagus; and (4) the hyp glossal nerve.

The medial branches are laryngo-pharyngeal and cardiac. T laryngo-pharyngeal branches, two or three in number, unite with t pharyngeal branches of the glosso-pharyngeal and vagus to formt pharyngeal plexus (see p. 1329).

The cardiac branch arises by two roots from the lower part of t superior cervical ganglion, and descends behind the carotid sheath, lyii medial to the main sympathetic trunk. The nerve of the right si passes in front of or behind the first part of the subclavian artery, ai then along the innominate artery, to end in the deep cardiac plexr In its course down the neck it receives twigs from the external larynge nerve, and is joined by the superior cervical cardiac branch of t] vagus nerve. As it enters the thorax it receives a filament from tl recurrent laryngeal nerve. The nerve of the left side within the thon accompanies the left common carotid artery, and passes in front the arch of the aorta to end in the superficial cardiac plexus.

The anterior branches are vascular, and pass to the external carot artery, upon which and its branches they form delicate plexuses.

Middle Cervical Ganglion. —This ganglion is situated opposite tl sixth cervical vertebra, and usually lies in front of the inferior thyro: artery. It is the smallest of the three, and is connected by gn rami communicantes with the fifth and sixth cervical nerves, thi representing two fused ganglia. Its branches of distribution a] thyroid and cardiac. The thyroid branches accompany the intern thyroid artery to the thyroid gland, and communicate with the extern; and recurrent laryngeal nerves. The cardiac branch of each side enc in the deep cardiac plexus. The nerve of the right side passes eith( in front of or behind the first part of the right subclavian artery. J then descends in front of the trachea, and joins the right half of tt deep cardiac plexus. The nerve of the left side enters the thora between the left common carotid and left subclavian arteries, and joins the left half of the deep cardiac plexus.


THE HEAD AND NECK


1335


Inferior Cervical Ganglion. —This ganglion is situated between the nsverse process of the seventh cervical vertebra and the neck of j first rib, where it lies behind the subclavian near the root of the rtebral artery. It is intermediate in size between the superior and ddle ganglia, and, like the middle, it probably represents two ganglia ited into one. It is frequently fused with the first thoracic ganglion, e connection between the middle and inferior cervical ganglia passes bind the subclavian artery, but sometimes a cord or cords in front the vessel form a loop around it, called the ansa subclavia (ansa mssenii). The inferior cervical ganglion is connected by grey ni communicantes with the seventh and eighth cervical nerves, and branches of distribution are vascular and cardiac. The vascular inches accompany the vertebral artery in the form of the vertebral •xus, which gives filaments to the vessel and offshoots along its rious branches. The plexus is continued along the basilar artery d its branches, and on to the posterior cerebral arteries. The rdiac branch on each side joins the deep cardiac plexus. The nerve the right side passes behind the first part of the right subclavian tery, and then in front of the trachea. It is connected with the rdiac branch of the middle cervical ganglion and recurrent laryngeal rves. The nerve of the left side in many cases joins the cardiac anch of the middle cervical ganglion, and so reaches the deep cardiac

iXUS.

Constitution of the Cervical Sympathetic Trunk.

The sympathetic trunk in the neck contains the following important groups of res: (1) dilator pupillae, (2) vaso-constrictor and vaso-dilator, (3) secretory, d (4) accelerator.

The dilator pupillae fibres are derived from the upper three thoracic nerves , d ascend in the sympathetic trunk to the superior cervical ganglion, in which 3y end. From this ganglion they are continued as sympathetic fibres to 2 medial part of the internal carotid plexus, through this plexus to the ciliary nglion, and thence to the dilator pupillae muscle.

The vaso-constrictor fibres are derived from a variable number of thoracic rves, beginning at the second and ending at the eighth, ihe origin of the SO-dilator fibres is not definitely known. The vaso-constrictor fibres ascend the superior cervical ganglion, in which they end. hrom this ganglion they 2 continued as sympathetic fibres into the plexus around the external carotid tery, and thence along the branches of that vessel.

The secretory fibres are destined for the submandibular gland, and are derived iefly from the second and third thoracic nerves. They also ascend to the perior cervical ganglion, in which they end. They are thence continued as mpathetic fibres into the external carotid plexus, from that into the facial 2xus, and thence into the submandibular ganglion, from which the} r pass into e submandibular and sublingual glands. .

The accelerator fibres of the heart are chiefly derived from the second and ird thoracic nerves, but some also spring from the first, fouith, and fifth nerves, le spinal fibres pass to the middle and lower cervical ganglia, from each of which ey are continued as sympathetic fibres.

The Mouth Cavity.

The cavity of the mouth extends from the oral fissure in front, here it opens externally on the face, to the oropharyngeal isthmus hind, where it opens into the pharynx. It is divided by the upper


A MANUAL OF ANATOMY


1336

and lower alveolar arches into two compartments, the anterior of wh: is called the vestibule and the posterior the mouth cavity proper.

The vestibule of the mouth is bounded anteriorly and externa by the lips and cheeks, and internally by the alveolar arches and gur Superiorly and inferiorly it is bounded by the reflection of the mucc membrane from the lips and cheeks on to the gums. In the medi line, above and below, the mucous membrane forms a small vertical f( called the frenulum. On the inner surface of each cheek the vestibu mucous membrane presents a small papilla opposite the second upj molar tooth, and on this is the minute opening of the parotid duct.

The mouth cavity proper lies within the alveolar arches. It co municates with the vestibule by the interval between the upper a lower teeth, and also by an opening at either side situated behind t last molar tooth. Anteriorly and externally it is bounded by t alveolar arches and gums, and posteriorly it opens into the phary by means of the oropharyngeal isthmus. The roof, which is arched, formed by the hard palate and the soft palate. The floor is form by the tongue, and the reflection of mucous membrane from the inr surface of the lower alveolar arch on to its under surface. In t region of the tip of the tongue the lateral reflections of mucous me] brane from the two sides of the lower alveolar arch are continuo across the median line. In the median line the mucous membra forms a prominent fold, called the frenulum linguce, which is co nected above with the under surface of the tongue a little distan from the tip. In some children it may extend quite to the tip, impa ing the utility of the organ, and giving rise to the condition known 'tongue-tied/ Close to each side of the frenulum there is a sm; papilla, on which is the opening of the submandibular duct. A litl posterior to this is a fold of the mucous membrane at either sic produced by the upper border of the subjacent sublingual glan This fold is known as the plica sublingualis, and it extends from t side of the tongue to the alveolar arch. It is upon this plica that tl majority of the sublingual ducts open.

The lips are covered by skin externally, and mucous membra] internally. Between these two layers are the muscular fibres of ti orbicularis oris, blended with which are the fibres of the buccinatc and in the case of the upper lip fibres of the depressor anguli or: whilst in the case of the lower lip there are the fibres of the levat anguli oris. Between the mucous membrane and the muscul element there are a number of small racemose glands, called the labi glands, the ducts of which open on the inner surface of each lip. Tl tortuous labial arteries are embedded in each lip, and those of opposi sides anastomose at the median line.

Between the upper lip and the columna nasi there is a groov called the philtrum.

The lymphatic vessels of the upper lip pass on either side to tl submandibular, to the submental, or to the superficial parotid lymp glands. The lymphatic vessels of the lateral portion of the lower 1


THE HEAD AND NECK


1337


50 pass on either side to the submandibular lymph glands, and ose of the medial portion pass to the submental lymph glands of the »rresponding side.

The cheeks are covered externally by skin, and internally are lined ith mucous membrane. The muscular element consists of the lccinator, which is covered by the buccal fascia. Posteriorly this scia is continuous with the pharyngeal fascia, which is derived from Le deep cervical fascia, the two being known as the bucco-pharyngeal scia. Superiorly and interiorly it is attached to the alveolar arches. The lymphatic vessels of the cheek pass to the superficial parotid lymph glands and the submandibular glands, the buccal lymph ands being a gland-station in the path of the latter.


Greater Palatine Artery


Palato-pharyngeus.^ $


Palato-glossus.


Posterior Wall of Pharynx^


Palatal RapW

.Uvula

Palato-pharyngeal Arch

^ '

Palatoglossal Arch ...Tonsil


. Dorsum of Tongue


u/ih " }i < <<(//{” ^\\v

jpUlin111.11


Fig. 804. —The Cavity of the Mouth and Oropharyngeal Isthmus.

The jaws are widely separated.


The suctorial pad of fat is situated upon the buccal fascia, and is ell developed in young children. It is continuous with the fat in le pterygoid region.

The buccal fascia, buccinator, and lining mucous membrane are ierced by the parotid duct. Between the buccinator and the mucous lembrane there are several racemose buccal glands. In addition to lese there are three or four molar glands, mucous in character, which re situated superficial to the buccal fascia in the angle between the lasseter and buccinator.

The masseteric fascia is an upward prolongation of the deep cervical iscia. It is attached superiorly to the zygoma, and externally is ontinuous with the parotid fascia.

The alveolar arches are formed by the alveolar borders of the laxillae and mandible, the teeth, and the gums.





1338


A MANUAL OF ANATOMY


The gums (gingivae) consist of dense fibrous tissue, which is covere by mucous membrane and is closely connected with the periosteum c the alveolar borders of the mandible and maxillae. The mucor membrane, which is very vascular, is continuous with the labial an buccal mucous membrane on the one hand, and with that of the floe of the mouth on the other. Close to the necks of the teeth it is bese with vascular papillae.

The lymphatic vessels of the upper gum pass on either side t the submandibular lymph glands. The lymphatic vessels of th lateral portion of the lower gum also pass on either side to the sut mandibular lymph glands; and those of the medial portion pass to th submental lymph glands of the corresponding side.

The mucous membrane of the gums is separated from the subjacen periosteum by dense connective tissue, which connects the two i: such a close manner that the mucous membrane is immovable. Clos to the necks of the teeth it is beset with papillae. The mucous mem brane of the hard palate, like that of the gums, is separated from th periosteum by a thick layer of dense connective tissue, which bind the two so closely that the mucous membrane is immovable. Ther is a median raphe, which is continued over the soft palate, and end in front at the incisive fossa in a small papillary elevation, known a the incisor papilla. On either side of the raphe anteriorly there ar a few transverse rugae. Each lateral half of the hard palate is traverse( by the ramifications of the greater palatine artery, the branches o which extend forwards and inwards from either lateral angle posteriorly The mucous membrane of the hard palate is provided with racemose palatal glands of a serous character, which are arranged in tw( symmetrical groups laterally disposed.

Occasionally a hard swelling, lying antero-posteriorly in the mid line of the hard palate, is seen, and must not be mistaken for a bom tumour or exostosis. It is known as the torus palatinus.

The lymphatic vessels of the mucous membrane of the hard palah pass to (i) the deep facial lymph glands, and (2) the superior deej cervical lymph glands.

Nerves. — The greater palatine nerve descends in the greatei palatine canal, which it leaves through the greater palatine foramen Then it divides into branches which pass forwards in groove! on the hard palate, and supply the mucous membrane, glands and inner aspect of the upper gum. The long spheno-palatine is distributed to the mucous membrane behind the incisor teeth, when it communicates with twigs of the greater palatine nerve. To react the hard palate the nerve of the right side passes through the posterior incisive foramen, whilst the left nerve passes through the anterio / foramen. The mucous membrane of the cheek is supplied by the buccal nerve, which is a branch of the mandibular division of the trigeminal nerve. The mucous membrane of the floor of the mouth derives its nerves from the submandibular ganglion.

Arteries.—These are the right and left greater palatine branches of


THE HEAD AND NECK


1339


e third part of the maxillary. Each greater palatine artery takes ie same course as, and has a similar distribution to, the greater palatine

rve. At the incisive fossa it terminates in a small branch which

cends through the lateral incisive canal, and anastomoses at the }per end of that canal with the posterior septal branch of the sphenoilatine artery.

Development of the Mouth, Lips, and Gums (pp. 70 & 85).

In the early stages of formation of the embryo, a transversely directed ink or furrow exists between the overhanging fore-brain and the prominent ricardium. This is known as the oral fossa or stomodaeum, and is frequently


Fig. 805.— Embryos of 10 Mm., 12 Mm., and 13*5 Mm.

ne first gives the facial aspect, the mandible being in situ, dhe maxillary process has not vet come against the fronto-nasal process. The 12 mm. specimen, seen from below after the mandible has been removed, shows the maxillary process meeting the fronto-nasal. The 13 ’5 mm. specimen, seen from below and somewhat from behind, shows the beginning of the extension of maxillary mesoderm over the fronto-nasal process. The primitive posterior naris can be seen in this embryo, in which the bucconasal plug has been destroyed, as a small point behind the maxillary extension and to the outer side of the globular or fronto-nasal process. Ihe corresponding point in the previous stage can be seen, but there is no apeiture. The early palate folds are recognizable. FN, fronto-nasal process; M, maxillary process, cut at its base; R, opening of Rathke s pouch, 11 , anterior margin of passage into tubo-tympanic recess.


erred to as an early stage in the developing mouth; it is, however, nearly, not altogether, replaced by forward growths from the wall of the pharynx, dosing between them the cavity of the adult mouth. ie stomodS6Um shut off from the pharynx by the bucco-pharyngeal membrane, formed by 3 meeting of the ectoderm lining the stomodaeum with the entoderm lining the arynx. The membrane is attached to the mandibular and maxillary pro

ses, is carried forward by these as they begin to grow, and is quickly broken

d lost.




x 34°


A MANUAL OF ANATOMY


The mandibular arch grows forward above the pericardium and male a new floor for the mouth. The maxillary processes grow forward on each sid


Fig. 806.— Plans showing Distribution of Maxillary Mesenchyme.

I. The early simple process reaches and just overlaps the hinder ends of tl nasal folds. Its outer and thicker part (Im, lateral mass, dotted) thii away internally, covering the paraxial mesoderm, and its inner part (s septal process, interrupted lines) comes against the inner fold; it do not reach the middle line, and Rathke’s pouch (R) is widely open.

II. The palate fold is a definite but blunt inner edge to the lateral mass, whi( has thickened greatly and is fusing in front with the inner nasal fol The septal process has reached the middle line in front and has spree over the neighbouring area of the fronto-nasal process. The opening is smaller, being compressed by deeper paraxial growth.

III. The extremity of the lateral part (having broken down the epithelial septu at their junction) has invaded the fronto-nasal region and is spreadii over it in front of the area covered by sp; this extension is going to for the alveolus and lip in this part. The septal process is coming into r lation with R, and reaches the middle line in front of this.

IV. Shows modifications in the lateral mass, which presents a labial edge (la and an alveolar eminence (alv) as well as a definite palate fold. Tl primitive posterior naris is represented as having extended to some degre showing that the septal process is forming the back part of the septu between the nares, thus explaining its name. The opening R, now on a point, has been caught between the process and its fellow, and has bee displaced slightly forwards, as indicated by the dotted line.

forming a side wall and lateral roof, and come up against the outer nasal fola cross these, and come into contact with the fronto-nasal process. Thus tl mouth has the mandibular arch and growing tongue as its floor, while its ro<



THE HEAD AND NECK


I 34 1

limited laterally by the deep maxillary processes, and in front by the frontosal process, with which the maxillary processes are joined.

Associated with the mouth are (i) the pouch of Rathke, (2) the tongue, the salivary glands, (4) the tonsils, and (5) the teeth.

The pouch of Rathke is a diverticulum of the roof of the ectodermic stomo:um, ventral to the bucco-pharyngeal membrane. Its development is given p. 87. It gives rise to the anterior lobe of the hypophysis cerebri, the posterior e of which is developed from a diverticulum of the floor of the third ventricle the cerebrum.

The development of the tongue, salivary glands, tonsils, and teeth will be md after the description of each of these organs.

Each early nasal cavity lies above and behind the fronto-nasal process, and opening into the mouth, very small, and closed at first by the bucco-nasal 'mbrane, is placed just above the junction of the maxillary with that process, te opening extends in an upward direction (see p. 85), and at the same time late folds make their appearance on the inner side of the maxillary processes >se to the outer edges of these openings. These folds are turned down and lie side the tongue, which occupies the cavity and is in contact with its roof, le folds run into the outer edges of the fronto-nasal process in front.


Globular Process


Maxillary Palatal Process Maxillary Process .


Oral Cavity


Palatal Part ot fronto-nasal Process t

i

Aperture of Olfactory Pit

Lens . Lye

Palatal Shelf

Pouch of Rathke


Fig. 807. —Roof of Mouth (Marshall, after His).

About the end of the ninth week—by which time the nasal openings have tended up to the highest level of the roof of the cavity—the palate folds me on to the dorsal surface of the tongue, as a result of this being carried below z fronto-nasal process by the growing mandible. They are now pressed against e ‘ edge ’ of the septum between the two openings, to which they adhere, us shutting off the lower parts of these openings from the mouth and making e hard palate. The folds meet behind the fronto-nasal process, which forms e incisive papilla. The incisive canals are in the angles between folds and ocess.

Lips (Labia Oris) and Gums (Gingivae).— Shortly after the fusion of the maxary and globular processes to form the maxilla, a groove appears along each

these processes on either side. The margins of this groove, which form irallel ridges, are external and internal relatively to the oral cavity. The ternal or labial ridge gives rise to the upper lip, the globular portion of the Ige representing the premaxillary part of the lip, and the maxillary portion rming the remainder. The internal or gingival ridge is the rudiment of the >per gum.

The philtrum is probably developed from the mesodermic investment of the lited globular processes.

A similar groove and similar ridges ( labial and gingival) appear along each andibular arch, and from the ridges the lower lip and lower gum are developed.




I 34 2 ‘


A MANUAL OF ANATOMY


The angles of the mouth correspond to the union between the two lips o: either side, and each originally represents the angle between a mandibular arc and maxillary process.


The Tongue.

The tongue is a muscular and very sensitive organ, covered tr the buccal mucous membrane, and situated on the floor of the mouth It is concerned in the sense of taste, mastication, deglutition, am speech, and it consists of a root or base, a body, and a tip. The roo is attached to the hyoid bone. The tip is the anterior free extremity


EpiglottisGlosso-epiglottis Fold


Foramen Caecum _javWw//| ijllbtes Lymphoid Tissue


Median RaplA


Palatopharyngeal Arch

AvTi *

Palatoglossal Arch

i vi/jI

/ Tonsil


^ Vallate Papillas


-Fungiform Papillae


Fig. 808.—The Dorsum of the Tongue.


which, in the quiescent state, lies behind the upper incisor teeth. The body has an upper surface or dorsum, an under surface, and two lateral borders, right and left. The dorsum is convex from before backwards, and on its anterior twoThirds is a median depression oi rap>he, on either side of which the surface is convex from side to side. This ends posteriorly in the foramen ccscum. In this region the dorsum has a V-shaped groove, known as the sulcus terminalis. The joint ol the V is at the foramen caecum, and the two limbs pass outwards and forwards to the sides of the tongue, where the palato-glossal arches are connected with it. The sulcus terminalis marks the union of the










THE HEAD AND NECK


1343


0 parts from which the tongue is developed. The part behind it, presenting one-third, is the basal, lymphoid, or pharyngeal portion, occupies the buccal part of the pharynx, and overhangs the epi)ttis. The portion in front of the sulcus terminalis, representing twoirds, is known as the buccal or papillary portion.

Mucous Membrane.—The mucous membrane covering the basal pharyngeal portion of the tongue is destitute of proper papillae, but freely provided with lymphoid follicles like those of the tonsils, d with mucous glands. The follicles are ranged upon the walls crypts, the mouths of which open upon the surface. The mucous embrane in this region forms the glosso-epiglottic fold, which is sdially placed. On either side of this fold, between it and each


Plica fimbriata


Frenulum


Plica sublingualis


Fig. 809. —Under Surface of Tongue, with Sublingual Region.


laryngo-epiglottic fold, there is a pouch or depression, called the llecula. In front of the sulcus terminalis the mucous membrane the dorsum, borders, and tip of the tongue is freely covered by laracteristic papillae, which, being visible to the naked eye, impart this part its distinctive appearance. These papillae bear secondary ipillae, which, however, are concealed by the epithelial covering. ie mucous membrane on the under surface of the tongue in the median ie forms near the tip a vertical fold, called the frenulum linguce. little lateral to the frenum on either side is an indistinct fringed Id, called the plica fimbriata. The two plicae converge as they pass rwards towards the tip, and inside each the outline of the vena mitans hypoglossi may be visible. They represent the under tongue sublingua of lemurs and marmoset monkeys. On either side of




j 344


A MANUAL OF ANATOMY


Epithelial

Covering


the tongue, in the region of the limbs of the sulcus terminalis, the mucous membrane presents a few ridges which represent the papilla foliata of such animals as the rabbit.

Papillae.—These are of four kinds—filiform, fungiform, circum vallate,and foliate—and they are confined to the anterior two-thirds of the organ. The filiform papillae are the most numerous, and are arranged in more or less parallel, closely-set rows, directed forwards

and outwards from the median line except towards the tip, where the rows tend to become transverse. Or the sides of the tongue they are arranged in vertical parallel rows.

The fungiform papillae are scattered amongst the filiform, and are most numerous at the sides and tip being rather sparse over the dorsum. Each is round and enlarged at the surface, but tapers at its deep end like a button mushroom, and it bears secondary papillae, but there is no thread-like processes on the epithelial caps.

The vallate papillae are conspicuous, and vary in number from seven to thirteen. They are arranged in two diverging rows which lie anterior to, and parallel with, the limbs ol the sulcus terminalis. The two rows converge backwards and inwards, and so form a capital V. In the median


- Papilla


Fig. 8io.—The Filiform Papillae of the Tongue.


line, at the point of the V, there is a single vallate papilla, behind which is the foramen caecum. The free surface of each papilla is broad and flat, and bears secondary papillae, whilst the deep end is somewhat constricted, and is received into a circular pit of the mucosa. In this manner each papilla is surrounded by a space known as the trench. The outer wall of the trench projects slightly beyond the level of the free surface of the papilla, thus forming a circular elevation around it, called the vallum (rampart). It is from this circumstance that the papillae have received the name ‘ vallate/ Their sides, as well as the wall of the vallum, contain the taste-buds.

The tongue contains a number of acinous glands. Some of them open into the trenches around the vallate papillae, where taste-buds are present, and are serous in character (Ebners glands). Others open into the foramen caecum, into the crypts on the posterior third of the dorsum, and along the sides of the organ, these being mucous in character (Weber’s glands). Beneath the apex of the tongue, on either side of the median line, there is a small group of glands, partly






















THE HEAD AND NECK


1345


ous and partly mucous. These two groups are known as the

erior lingual glands (glands of Blandin or of Nuhn).


Fig. 811.—Extrinsic Muscles of Tongue.


The muscular tissue of the tongue is of the striped variety. It ms two sets of muscles—namely, extrinsic and intrinsic. The


Taste-bud


B


Fig. 812.—Vertical Section of a Vallate Papilla of the Tongue.

A, vallate papilla, beset with secondary papillae; B, taste-bud,

C, gustatory cell.

trinsic muscles are those which have their origins outside the tongue, id their insertions into it. They are: (1) the genio-glossus, (2) the














A MANUAL OF ANATOMY


1346


hyo-glossus (including the chondro-glossus), (3) the stylo-glossus, ai (4) the palato-glossus, all of which have been already described. T intrinsic muscles are those which are contained entirely within t tongue, and are: (1) the longitudinalis superior, (2) the longitudina inferior, (3) the transverse linguae, and (4) the verticalis linguae.

The longitudinalis linguae superior is an expanded sheet placed < the dorsum immediately beneath the mucous membrane. Its fibi are disposed longitudinally, and the muscle extends from the t backwards to the body of the hyoid bone. Posteriorly it is ovf

lapped by fibres of the hyo-glossi


Fig. 813. —Longitudinal Section of the Tongue of a Cat (injected).


1. Muscosa M

2. Longitudinal Superior

3. Transversus et Verticalis Linguae

4. Longitudinalis Inferior


Its fibres do not extend over t. whole length of the tongue, b take attachment at short intervc to the mucous membrane.

The longitudinalis linguae inf eri is disposed as a round bundle ( the inferior surface of the tongu Posteriorly it lies between the i sertions of the genio-glossus mec ally and the hyo-glossus laterall and anteriorly fuses with the styl glossus laterally. The muscle e: tends from the tip of the tongi to the body of the hyoid bone, wil which it is connected.

The transversus linguae const tutes a layer of considerable thicl ness which is placed between tl longitudinales superior et inferio It arises from the median septun and extends outwards, the upp< fibres curving upwards, to be ii serted into the mucous membrar of the side of the tongue an adjacent portion of the dorsun This muscular stratum is intei spersed with fat, and is muc


broken up by fibres of the verticalis linguae and genio-hyo-glossus.

The verticalis linguae extends from the mucosa of the dorsum that of the inferior surface. Its fibres describe curves, having tl convexities directed inwards, and they decussate freely with tl fibres of the transversus linguae.

Septum Linguae.—The septum of the tongue is a fibrous partitic which extends in the median line from the tip of the organ to tl body of the hyoid bone. It divides the tongue into two symmetric halves, and the transversus linguae muscle arises from it on eitb side.

Arteries.—( 1 ) The arteria profunda linguae (ranine artery), which :




















































THE HEAD AND NECK


1347


  • anch of the lingual, and is situated on the inferior surface immediy lateral to the line of insertion of the genio-glossus muscle. It

stomoses with its fellow beneath the tip, but elsewhere there is no stomosis across the septum linguae. (2) The dorsalis linguae, ally several branches. (3) The tonsillar branch of the cervical ion of the facial artery. (4) Pharyngeal branches of the ascending ryngeal artery.

The veins pass to the internal jugular vein.

Lymphatics.—The lymphatic vessels of the tongue are disposed in ' groups —apical, marginal, basal, and central.

The apical lymphatics pass to the submental lymph glands of the Le side, and to one of the medial chain of deep cervical lymph glands a. level with the cricoid cartilage of the larynx.

The marginal lymphatics carry lymph from the anterior twods of the lateral border and marginal part of the dorsum. The trior lymphatics of this set turn round the mylo-hyoid muscle,

. end in the anterior submandibular lymph glands. The posterior s to the superior deep cervical lymph glands, and more particularly one lying deep to the angle of the mandible. The small lingual ids, which lie upon the outer surface of the hyo-glossus muscle, je as gland-stations in their path.

The basal lymphatics return lymph from the posterior third of the gue, and end in the same way as the posterior marginal lymphatics t stated.

The central lymphatics return lymph from the median part of the gue, and pass to the deep cervical lymph glands, which extend from posterior belly of the digastric muscle to the level of the cricoid tilage of the larynx.

Nerves.—The sensory nerves are: (1) the lingual branch of the vidibular nerve , which is distributed to the mucous membrane over anterior two-thirds of the tongue, including the filiform and fungin papillce, upon which it confers common sensibility; (2) the rda tympani nerve, which accompanies the lingual nerve to the erior two-thirds of the tongue, of which it is usually regarded as nerve of taste; (3) the lingual branch of the glosso-pharyngeal ve, which is distributed to the mucous membrane of the posterior d and to the vallate papillce , of which it is the nerve of taste; (4) the irnal branch of the superior laryngeal nerve, which furnishes a few gs to the mucous membrane of the root of the tongue in the region the epiglottis; and (5) the hypoglossal nerve, which supplies the pial muscles.

Sympathetic filaments are also conducted to the tongue by the

  • ious arteries.

Taste-buds.—These gustatory organs are modified epithelial cells, 1 are present in the following situations: (1) The sides of the vallate fillae and the opposed surface of each vallum; (2) the sides of the

erior two-thirds of the tongue, partly in connection with the fungim papillae, and partly embedded in the stratified epithelium; (3) the



1348


A MANUAL OF ANATOMY


folds which form the papilla foliatce ; (4) the buccal surface of the s palate; and (5) the posterior surface of the epiglottis.

Each taste-bud is a flask-shaped body. The base rests upon 1 corium of the mucosa, and gives passage to nerve-fibres. The a] or narrow end lies between the surface-cells of the epithelium, a it is perforated by a minute opening called the gustatory pore , thror which the peripheral processes of the gustatory cells in the inter of the bud project as gustatory hairs.

Structure.—The wall of a taste-bud is composed of flatten* nucleated, epithelial walls, called the supporting cells. These cc are elongated in the direction of the bud, they taper at either ei and their margins are closely applied to each other. The interior the bud consists of . a bundle of gustatory cells. Each gustatory c is nucleated and spindle-shaped. The body of the cell is prolong at either end into a process, peripheral and central respectively. T peripheral process passes to the gustatory pore at the apex of the bi


Fig. 814.—The Visceral Arches of the Embryo (Posterior View) (Hi

I. Mandibular Arch III. Thyrohyoid Arch

II. Hyoid Arch IV. Fourth Arch


through which it projects as a gustatory hair. The central proce passes towards the base of the bud, which rests upon the corium 1 the mucosa. It is usually branched, and ends in free extremitie It does not therefore become continuous with nerve-fibres, and therei it differs from the corresponding process of an olfactory cell.

It has been seen that the base of each taste-bud gives passage i nerve-fibres. These, as they enter the bud, lose their medullar sheaths, and their axons end within the bud in arborizations aroun the constituent gustatory cells. Nerve-fibrils also enter the ep thelial wall of the bud, and ramify between the supporting cells.

Development. —The tongue is developed in the floor of the pharynx in tw parts—buccal and pharyngeal—which are separated from each other by th foramen caecum and V-shaped sulcus terminalis (see p. 72)."

The buccal or papillary part, which represents the anterior two-thirds, : developed from the tuberculum impar of the first or mandibular visceral arcl This eminence may give rise to the portion of the buccal part directly in fror of the foramen caecum.











THE HEAD AND NECK


  • 349


I'his, which appears very early, is a small rounded and well-defined swelling he middle line of the pharyngeal floor; it is in the line of the first pharyngeal )ve, but appears to belong really to the mandibular arch. It enlarges slowly


g 8is) but clearly as a separate formation, into which extend, fiom below 1 behind, the paired anterior ends of the ventral down-growths from post? (occipital) myotomes; with these the hypoglossal nerves and lingual vessels

ch the tongue.





  • 350


A MANUAL OF ANATOMY


This account is in keeping with the observations made on embryo material of all the stages involved. The usual description, that paf swellings on the mandibular arch envelop and in this way obliter; the tubercle as a separate structure, appears to have little support in f; (Fig. 815).

The pharyngeal or basal part of the tongue, the portion lying behind 1 foramen caecum and sulcus terminalis, is made from forward extension of 1 anterior end of the hypobranchial eminence coming against the back of the grc ing tuberculum impar and extending behind it and postero-laterally. 1 actual mass which comes forward in this way is probably a third arch derivati the mesoderm of this arch extending into and covering the anterior end of 1 hypobranchial eminence; the second arch, which at one time seems to rea the eminence also, is overpowered by the third arch growth, which covers it a comes forward above it. This is a part of the general movement in the pharyngi floor in which the second arch drops completely out of the floor, except in t tympanum, the third arch passing forward over it and coming against the fi: arch in front of it. In the middle, the third arch masses apply themselves the back of the tuberculum impar, and in doing so enclose temporarily a sm entoderm-lined space which opens by a relatively wide aperture, the futr foramen ccecum. This space would have the thyroglossal duct inserted into floor, if the duct had not separated (apparently) from it long before. The spa gradually fills up, as a rule, and the ‘ opening ' becomes the definitive foram caecum. Thus the foramen caecum is not the actual impression of the thyrc outgrowth, but, owing to the way in which it comes into existence, it is behind t tuberculum impar, and thus marks on the surface the spot from which—b at a deeper level—the thyroid growth took place.


The Soft Palate.

The soft palate is a movable musculo-aponeurotic curtain situah at the back part of the hard palate, where it projects downwards ar backwards into the pharynx. Anteriorly it is attached to the posters border of the hard palate, laterally it is connected with the side < the tongue and the wall of the pharynx, and postero-inferiorly it h; a free border. Its surfaces, which occupy an oblique plane, a; antero-inferior or buccal, which is concave, and postero-superior ( pharyngeal, which is convex and looks towards the naso-pharyn: The postero-inferior border at its centre has a conical proces called the uvula. On either side of the base of the uvula the] are two prominent folds of mucous membrane, which extend ou wards and downwards in a diverging manner. These constitul the palato-glossal and palato-pharyngeal arches (anterior and posteric pillars of the fauces). Each palato-pharyngeal arch belongs to tt postero-inferior border of the soft palate, and it sweeps outward downwards, and backwards to the lateral wall of the pharynx. 1 is due to the palato-pharyngeus muscle. Each palato-glossal arc belongs to the buccal surface of the soft palate, and it sweeps ou wards, downwards, and forwards to the back part of the side of tt tongue. It is produced by the palato-glossus muscle. Between th diverging palato-glossal and palato-pharyngeal arches on either sid there is a triangular interval, which is occupied by the tonsil. Tt passage which leads from the buccal cavity into the pharynx is calle the oropharyngeal isthmus (isthmus of the fauces). It is somewha


THE HEAD AND NECK


I35i


istricted, and is bounded above by the soft palate, below by the

k part of the dorsum of the tongue, and on either side by the

[ato-glossal arch.

Structure. —The soft palate is composed of a double fold of mucous imbrane, which contains between its two layers an aponeurosis, iscles, and many racemose glands, with bloodvessels and nerves, e mucous membrane on the buccal surface has a median raphe, iich is continuous with that on the mucous membrane of the hard late, and along which the originally separate halves of the soft late unite. On the buccal surface and along the postero-inferior rder it is covered by stratified squamous epithelium, but on the aryngeal surface by ciliated columnar epithelium. The glands.



Greater Palatine Artery


Palate pharyngeus __


Pnlato-glossus


Posterior Wall of Pharynx


Palatal Raph6


- Uvula

Palato-pharnygeal Arch —-Palato-glossal Arch

— Tonsil


Dorsum of Tongue


biG. 816 .—The Cavity of the Mouth and Oropharyngeal Isthmus.

The jaws are widely separated.


hich are racemose or acinous, are especially abundant on the buccal irface beneath the mucous membrane, where they are closely packed igether. The palatine aponeurosis is attached anteriorly to the Dsterior border of the hard palate, and laterally it becomes continuis with the aponeurosis of the pharynx. It affords attachment to artions of the palatal muscles.

Muscles.— These are arranged in pairs, and are palato-glossus, alato-pharyngeus, musculus uvulae, levator palati, and tensor palati.

Palato-glossus— Origin .—The surface of the palatine aponeurosis, is fibres being continuous across the middle line with those of the pposite muscle.

[ Insertion —The back part of the side of the tongue, where its bres blend with the fibres of the transversus linguas.






1352


A MANUAL OF ANATOMY


Nerve-supply. —The pharyngeal plexus.

The direction of the muscle is outwards, downwards, and forward Action. —(i) To depress the side of the soft palate, and (2) draw the tongue upwards and backwards. The two muscles al‘ approximate the palato-glossal arches. By means of these combine actions, aided by the tongue, the oropharyngeal isthmus is close< and the anterior part of the buccal cavity is shut off from the pharyn at the beginning of the second stage of deglutition.

The muscle forms the lowest layer in tt soft palate, and it gives rise to the mucoi fold, called the palato-glossal arch.

Palato - pharyngeus — Origin. — By tw layers, upper and lower. The posterior (uppei small layer arises from the palatine aponei rosis of the back of the soft palate abov the musculus uvulae, its fibres decussatin with those of the opposite side; and th anterior (lower) large layer arises from th posterior margin of the hard palate, as we as from the palatine aponeurosis, decussatin with its fellow of the opposite side.

Insertion. —(1) The superior and posterio borders of the lamina of the thyroid cartilage and (2) the lateral and posterior wall of th pharynx, its fibres blending with those 0 the stylo-pharyngeus.

The muscle receives an accessory sli] from the lower part of the cartilage of th pharyngo-tympanic tube, which is known a: the salpingo-pharyngeus muscle.

Nerve-supply .—The pharyngeal plexus. The muscle is directed downwards anc backwards.

Action. —(1) To approximate the palatopharyngeal arch to its fellow at the commencement of the second act of deglutition, and (2) to elevate the pharynx.

The muscle gives rise to the mucous fold called the palato-pharyngeal arch.

Musculus Uvulae (Azygos Uvulae)— Origin. — The side of the posterior nasal spine and the adjacent palatine aponeurosis.

Insertion. —The submucous tissue of the uvula, having previously united with its fellow of the opposite side.

Nerve-supply. —The pharyngeal plexus. The direction of the muscle is backwards and downwards.

Action. —To elevate and shorten the uvula.

The muscle is double at its origin, but single at its insertion. It


Fig. 817.—Scheme to show Planes in Composition of Pharyngeal Wall, with Relation of Muscles to Mucous Membrane (Dotted Line).

SUP., MID., INF., upper, middle, and lower constrictors. Sinus of Morgagni is the interval between upper constrictor and skull base; the tube is seen coming through this.




THE HEAD AND NECK


1353


s above the levator palati, and beneath the upper layer of the lato-pharyngeus.

Levator Palati— Origin. —(1) The rough surface on the inferior pect of the petrous part of the temporal bone between the apex d the carotid canal, and (2) the lower and posterior part of the rtilage of the pharyngo-tympanic tube.

Insertion. —The aponeurosis of the soft palate, its posterior fibres coming continuous across the middle line with the corresponding res of the opposite muscle.


Tubal Elevation


Posterior Border of the Vomer

Right Posterior Nasal Aperture Levator Palati




Salpingopharyngeus

Musculus Uvulae

Palato pharyngeus


Tensor Palati


-Medial Pterygoid Uvula

l- Root of Tongue


-- Epiglottis Wall of Pharynx

- Piriform Fossa

Arytenoideus Obliquus

- Arytenoideus Transversus


— Crico-arytenoideus Posterior


(Esophagus


Fig. 818. —The Pharynx opened from Behind.


Nerve-supply. —The pharyngeal plexus.

The muscle is directed downwards, forwards, and inwards.

Action. —To raise the soft palate, and probably to open the pharyngonpanic tube.

The muscle, which is round and fleshy, passes over the upper rder of the superior constrictor and through the pharyngeal apon:osis. At its origin it is closely related to* the membranous portion the pharyngo-tympanic tube.

Tensor Palati— Origin. —The scaphoid fossa at the root of the dial pterygoid plate of the sphenoid; and the ridge running back far as the spine; and the lateral lamina of the cartilage of the iryngo-tympanic tube.







1354


A MANUAL OF ANATOMY


Insertion. —(i) The transverse ridge on the under surface of th horizontal plate of the palatine bone near the posterior border; an (2) the aponeurosis of the soft palate.

Nerve-supply .—A branch from the nerve to the medial pterygoi muscle.

The muscle at first descends vertically as a flat fleshy band betwee the medial pterygoid plate and the medial pterygoid muscle, bein in close contact with the medial surface of the latter. As it approache the pterygoid hamulus it ends in a tendon, which turns round th process, a synovial bursa intervening, and then passes horizontal! inwards, expanding as it does so. From the fact that the muscle i bent around the pterygoid hamulus it has been called the circum flexus palati.

Action. —(1) To make tense the soft palate, and (2) to draw dowr wards and backwards the margins of the cartilage of the pharyngc tympanic tube, and so open the tube during deglutition. (See actio: of levator palati.)

Sensory Nerves. —These are the greater and lesser palatine nerve from the spheno-palatine ganglion, and the tonsillitic branches of th glosso-pharyngeal.

Arteries. —The soft palate is supplied by the following arteries (1) the ascending palatine of the cervical portion of the facial; (2) th palatine branch of the ascending pharyngeal; and (3) the lesse palatine branches of the greater palatine artery from the maxillary which descends in the greater and lesser palatine canals.

Relation of Structures in the Soft Palate. —Supposing the sof palate to be transfixed from its buccal to its pharyngeal surface, th following structures would be pierced: (1) the mucous membran covering the buccal surface, (2) the layer of closely-set racemos glands, (3) the palato-glossus, (4) tensor palati, (5) the lower laye of palato-pharyngeus, (6) the levator palati, (7) the musculus uvula (8) the upper layer of the palato-pharyngeus, and (9) the mucou membrane covering the pharyngeal surface.

Development. —The soft palate is developed from a differentiated portioi of the palatal shelf or plate of the maxillary process of either side. This different! ated portion does not undergo ossification, but acquires muscular tissue. Lik the hard palate, the soft palate and the uvula are developed in two symmetrica halves. The muscular tissue is derived from an upward growth from the wal of the pharynx invading the posterior part of the (maxillary) palate fold. Thi upgrowth makes the ‘posterior pillar of the fauces.’


The Tonsils.

The tonsils are two in number, right and left. Each is situatec in the triangular depression between the palato-glossal and palato pharyngeal arches on either side, and above it is a small recess, knowi as the intratonsillar cleft (supratonsillar fossa), which is the remain: of the inner portion of the second visceral cleft. The tonsil stands ou as an oval enlargement covered by mucous membrane, and it lie;


THE HEAD AND NECK


1355


posite the angle of the mandible, being under cover of it and the jacent portion of the ramus. The organ varies much in size, but an average it measures about 1 inch in length, about f inch from fore backwards, and about \ inch from within outwards. The 3dial surface is pitted with a number of orifices which lead into crypts the interior. The outer surface, which has a fibrous covering, is ated to the superior constrictor of the pharynx, some loose tissue tervening, and lateral to the superior constrictor is the medial erygoid muscle. Two of the tonsillar arteries, the tonsillar and sending palatine, lie between the superior constrictor and medial erygoid. The cervical portion of the facial artery in its course lies little below the outer aspect of the tonsil. The internal carotid tery is situated about 1 inch from it on its outer and posterior aspect. Arteries.—(1) The tonsillar and ascending palatine branches of e facial; (2) the ascending pharyngeal branch from the external rotid; (3) the dorsalis linguae branches from the lingual; (4) the


Fig. 819. —Section through a Crypt of the Tonsil.

iser palatine offsets of the greater palatine artery from the third rt of the maxillary; (5) tonsillar twigs from the internal carotid.

The veins form a plexus on the outer surface of the tonsil, from lich the blood passes into the pharyngeal plexus.

Lymphatics.—These pass to the superior deep cervical lymph mds.

Nerves.—The nerves are derived from (1) the glossopharyngeal, > the lesser palatine branches of the spheno-palatine ganglion, and ) the sympathetic.

Structure. —The tonsils are composed of lymphoid follicles. The follicles i ranged upon the sides of the crypts, which penetrate into the organ, these /pts being lined with mucous membrane covered by stratified squamous ithelium. Lymph corpuscles migrate from the follicles into the crypts, and

ome salivary corpuscles.

Development. —The tonsil of either side is developed from the epithelium the ventral part of the corresponding second visceral cleft. About the fourth 1 nth a depression, known as the sinus tonsillaris, makes its appearance. Solid




1356 A MANUAL OF ANATOMY

epithelial outgrowths or buds then extend from this sinus into the surroundinj mesoderm. These buds subsequently become hollow, the surface of the sinu becomes pitted, and so the crypts on the tonsil are formed. The mesoderm ii relation to the buds and crypts becomes pervaded with lymphoid cells, and ii this manner is formed the lymphoid tissue which constitutes the bulk of the tonsil The intratonsillar cleft indicates the position of the ventral angle of th< second lateral pouch.

The Nasal Cavity.

The nasal cavity extends from the anterior to the posterior aperture of the nose. Anteriorly it opens upon the face, and posteriorly int( the nasal part of the pharynx. The cavity is narrow above, bu


Fig. 820.—Sagittal Section through the Nasal Cavity, Mouth, Pharynx, (Esophagus, and Larynx.

The outer wall of the right nasal cavity is shown.


expanded below. It is divided into right and left halves by the nasal septum, and each half has two walls (outer and inner), a roof, and a floor. The lateral wall is rendered very irregular by three bony scrolls, disposed antero-posteriorly, which bulge into the fossa. These are the superior, middle, and inferior nasal conchae. They overhang deep channels, which are known as the meatus—superior, middle, and inferior respectively.

The superior meatus is confined to the back part of the outer wall,












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id lies between tlie supeiior and middle conchae. It is short and clique, and opening into it there are the spheno-palatine foramen, hich leads from the pterygo-palatine fossa, and the posterior ethoidal sinus, by one or more openings. Above and behind the Lpenor concha is a depression, called the spheno-ethmoidal recess, to which the sphenoidal sinus opens.

The middle meatus is situated between the middle and inferior >nchae, is directed from behind forwards, and is overhung by the iddle concha. Anteriorly it describes a bend, and passes upwards ider coyer of the front part of the middle concha, to be continued to the infundibulum , which leads from the frontal sinus of the corre>onding side. The openings into the middle meatus are (1) the fundibulum, leading from the frontal sinus, with the opening of the iterior ethmoidal sinus * (2) the opening of the maxillary sinus;


Frontal Sinus


Orifice of Naso-lacrimal Duct


Vestibule


Fig. 821.—The Lateral Wall of the Right Nasal Cavity.

The superior and middle conchae and part of the inferior concha have

been removed.

id (3) one or two openings of the middle ethmoidal sinus. These irious openings are concealed by the middle concha. When this is moved a deep curved groove, called the hiatus semilunaris, is seen rected downwards and backwards from the lower end of the inndibulum. Behind and above this hiatus there is a round promince, called the bulla ethmoidalis (see Fig. 821). The opening of e anterior ethmoidal sinus is situated in the vertical portion of the atus semilunaris, and the opening of the maxillary sinus, which is small size, is placed in its horizontal portion, whilst the middle hmoidal sinus opens above the bulla ethmoidalis. In front of the iddle meatus is the region known as the atrium, which communicates teriorly with the vestibule, situated just within the ala of the nostril. The inferior meatus is situated below the inferior concha. Openl into its anterior part, under cover of the inferior concha, is the





A MANUAL OF ANATOMY


1358


lower orifice of the naso-lacrimal duct, which is provided with an im perfect mucous fold, called the lacrimal fold. The orifice is abou ij inches from the anterior nasal aperture. Quite often the superio nasal concha bifurcates posteriorly, and thus encloses a fourth o highest meatus.

The inner wall forms the nasal septum.

The roof, which is narrow, is horizontal in its central part, th anterior portion being sloped downwards and forwards, and th posterior portion downwards and backwards.


Sphenoidal Sinus


Perpendicular Plate of Ethmoid


Frontal Sinus


Nasal Bone


1 Septal Process of Lower Nasal Cartilage


Horizontal Plate of Palatine Bone (in section)


Septal Cartilage


Vomero-nasal Cartilage


Vomer


Palatine Process of Maxilla (in section)


Fig. 822.—The Osseous and Cartilaginous Nasal Septum (Right

Lateral View).


The floor is smooth, and at its anterior and inner part is the incisoi foramen, into which a funnel-shaped portion of the mucous membrane extends. This region represents the wide communication whicl existed in early life between the nasal and buccal cavities.

Each nasal cavity is divided into three regions—vestibular, olfactory, and respiratory. The vestibular region, or vestibule, form: the anterior and lower part near the nostril. It is covered by skin which is provided with hairs or vibrissce. The olfactory region i: situated superiorly, and corresponds to the superior concha and th<


/








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1359


er third of the nasal septum. The respiratory region comprises middle and inferior conchae, the middle and inferior meatus, and corresponding part of the septum.

The Nasal Mucous Membrane. —With the exception of the vestibule, ch is lined with skin, the nasal cavity is provided with a highly sular and sensitive mucous membrane. It is continuous through the terior nasal apertures with the mucous membrane of the nasal part the pharynx; with that of the naso-lacrimal duct, lacrimal sac,

. lacrimal canaliculi, and thence with the conjunctiva; and with t of the various air-sinuses which communicate with the nasal ity. It is thick and spongy over the conchae, especially along the er borders of the middle and inferior conchae, and also on the nasal turn, but over the floor, atrium, and meatus it is comparatively


Fig. 823. _ The Nerves of the Nasal Septum (Hirschfeld and

Leveille).


n. It is freely provided with acinous glands, and contains a certain

ount of lymphoid tissue. •

The epithelium varies in different regions. In the vestibular ion, where the lining membrane is skin, it is of the stratified squamous 'iety; in the respiratory region, as well as in the air-sinuses, it is itified, columnar, ciliated epithelium; and in the olfactory region s non-ciliated columnar epithelium.

Olfactory Mucous Membrane. —In the olfactory region the mucous mbrane is thick and pulpy, and has a yellowish-brown colour, 3 to pigment in the epithelial cells. It contains a copious plexus olfactory nerve-fibres, and many serous glands, which are known the nasal glands (Bowman s glands). The epithelium is thick, and, as 5 been shown, is of the non-ciliated columnar variety, its free surface ng covered by a delicate limiting membrane. The cells of whic








1360


A MANUAL OF ANATOMY


it is composed are of three kinds: (1) Long columnar nucleated cel called the supporting cells, the deep end of each of which is prolong into a branched process. (2) Between these supporting cells the are the olfactory cells, which are elongated and spindle-shaped. Ea contains an almost spherical nucleus, and has a superficial and a de process or pole. The superficial pole extends through the limiti

membrance to the free surface, and pi jects slightly in the form of a tuft delicate hair - like filaments called t olfactory hairs. The deep pole , which a delicate varicose filament, exten towards the mucosa, where it becom continuous with one of the nerve-fibr of the olfactory plexus. (3) In the de part of the epithelium there are in sor places conical cells, the broad ends which rest upon the basement membra (see Fig. 824).

Olfactory Nerves. —These are from f teen to twenty in number on each sic After leaving the inferior surface of t olfactory bulb, they pass through t foramina in the corresponding half of t cribriform plate of the ethmoid bor and so reach the upper part of the nas cavity invested by prolongations of t membranes of the brain. Within t nasal cavity they are arranged in t\ groups, inner and outer. The nerves the inner group are distributed to the mucous membrane of the nas septum over about its upper third. The nerves of the outer group a distributed to the mucous membrane in the region of the superi concha and olfactory sulcus. The nerves form a copious plexus the mucous membrane, and the filaments which issue from this plex become continuous, as has been shown, with the deep poles of t olfactory cells. The olfactory nerves have no medullary sheath.

Nerves of Ordinary Sensation:

1. Upper nasal branches of the

spheno-palatine ganglion.

2. Nasal branches of the nerve of

the pterygoid canal.

3. Lower nasal branches of the

greater palatine nerve.

The upper nasal branches of the spheno-palatine ganglion enter the superi meatus through the spheno-palatine foramen, and are distributed to the muco membrane (1) over the superior and middle conchae, (2) over the upper ai back part of the nasal septum, and (3) within the posterior ethmoidal sinus.

Branches from the nerve of the pterygoid canal pierce the floor of that can; and are distributed to the mucous membrane over the back part of the roof the nasal cavity and the adjacent part of the septum.


4. Anterior ethmoidal nerve.

5. Branches of the anterior superi

dental nerve.

6. Long spheno-palatine nerve.

7. Infra-orbital nerve.



Olfactory _ Hairs ||


Peripheral

Process


Supporting

Cell


Olfactory li Cell ha


Nerve Fibre V. Process


Fig. 824.— Cells of Olfactory Mucous Membrane

(SCHULTZE, FROM QuAIN’S

‘ Anatomy ’)•












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1361


Lower nasal branches arise from the greater palatine branch of the sphenolatine ganglion as that nerve traverses the greater palatine canal. They ter the nasal cavity through foramina in the perpendicular plate of the latine bone, and are distributed to the mucous membrane over the greater rt of the inferior concha, and the corresponding parts of the middle and ferior meatus.

The branches from the anterior ethmoidal nerve are two, septal and lateral, le septal branch is distributed to the mucous membrane over the anterior and >per part of the septum, and the lateral branch to that over the anterior irtions of the middle and inferior conchae, and over the outer wall in front these.

Upper nasal branches of the anterior superior dental nerve are distributed to e mucous membrane over the anterior part of the inferior meatus and the !jacent part of the floor of the nasal cavity.

The infra-orbital branch of the trigeminal supplies the vestibule.

Anterior Ethmoidal Arterv


Fig. 825. —The Arteries of the Nasal Septum (Hirschfeld and

Leveille).

It will be noticed that, with the exception of the anterior ethmoidal branch of te naso-ciliary, all the nerves of the nasal cavity are derived from the maxillary vision of the trigeminal nerve.

The long spheno-palatine nerve arises from the spheno-palatine ganglion, id enters the nasal cavity through the spheno-palatine foramen. It then osses the roof, and so reaches the septum, upon which it descends with a rward inclination, occupying the groove on the outer surface of the vomer.

then passes downwards to the anterior part of the hard palate, the left nerve aversing the anterior incisive canal, and the right nerve the posterior incisive nal. As the long spheno-palatine nerve lies upon the nasal septum it furnishes anches to its mucous membrane.

Arteries of the Nasal Cavity. —These are derived from the following sources:

1. The spheno-palatine. 4. The anterior ethmoidal.

2. The greater palatine. 5 - The posterior ethmoidal.

3. The artery of the pterygoid canal. 6. The superior labial.

The spheno-palatine artery is the principal artery of the nasal cavity. Arising am the third part of the maxillary, it enters the cavity through the sphenoilatine foramen. Most of its branches are distributed to the outer wall; but

86






1362


A MANUAL OF ANATOMY


one, called the posterior septal branch, accompanies the long spheno-palati nerve. This branch gives offsets to the septum, and enters the incisive forame where it anastomoses with a branch of the greater palatine artery, which ascen from the palate in the incisive canal.

The greater palatine artery arises from the third part of the maxillary. . it traverses the greater palatine canal it gives off two or three branches whi accompany the lower nasal branches of the greater palatine nerve throu, foramina in the perpendicular plate of the palate bone, to be distributed to t back part of the inferior concha and the adjacent parts of the middle and i ferior meatus.

The artery of the pterygoid canal, arising from the third part of the maxillai traverses the pterygoid canal, and furnishes a few twigs which accompany t branches of the corresponding nerve, and supply the back part of the roof the nasal cavity and the adjacent part of the septum.

The anterior and posterior ethmoidal arteries are branches of the ophthalm The anterior ethmoidal enters the nasal cavity along with the anterior ethmoid


Posterior Lateral Nasal Branches


Anterior EthmoiiJal


Posterior Ethmoidal

Posterior Septal Branch (cut) Spheno-palatine


Ascending Branch of Greater Palatine


Soft Palate


Fig. 826. —-The Arteries of the Lateral Wall of the Right Nasal Cavity, (after Hirschfeld and Leveille).

nerve, and furnishes branches to the anterior and upper part of the septur the front part of the outer wall, and the anterior portions of the middle ar inferior conchae. The posterior ethmoidal gives nasal branches which enter tl nasal cavity through some of the foramina in the cribriform plate of the ethmoii and are distributed to the roof and upper part of the septum.

The superior labial artery, a branch of the facial, gives off a septal branc, which supplies the anterior part of the septum and the columna nasi.

The veins form a free plexus, especially over the inferior concha and tl lower margin and back part of the middle concha. The vessels which can away the blood from the plexus correspond to the various arteries, and the principal destination is threefold—namely, (1) the pterygoid plexus, (2) th superior ophthalmic vein, and (3) the anterior facial vein. The ethmoidal vein which open into the superior ophthalmic vein, communicate with the intracrani; anterior meningeal veins and with the commencement of the anterior faci< vein by means of twigs which pass through minute apertures in the front* process of the maxilla, and, it may be, through a small foramen in the nas; bone. In those cases where the foramen caecum is pervious it transmits a









THE HEAD AND NECK 1363

issary vein which passes between the intracranial superior sagittal sinus 3 the veins of the roof of the nasal cavity.

The lymphatics of the atrium and vestibule pass to the submandibular lymph nds. The principal lymphatics pass to (1) the retropharyngeal glands; (2) the ip facial lymph glands; and (3) the superior deep cervical lymph glands, e lymphatics of the air-sinuses end in a similar manner.

The lymphatics of the nasal fossae communicate with lymphatic spaces ich are related to the olfactory nerve-filaments; and these lymphatic spaces turn communicate with the intracranial, subdural, and subarachnoid spaces.


Development of the Nose (pp. 83-88).


The cavity of the mouth in the embryo is separated from the lower surface the fore-brain and its derivatives by a layer of mesoderm which thickens titinuously. The nasal cavities are developed in this mesodermal layer, and as are not parts of the common mouth cavity', they open into this cavity by ertures which lengthen as the mesoderm thickens, and of which the greater rtions are secondarily closed by the palate folds, the unclosed parts forming e definite posterior nasal apertures.

The first indications of the olfactory organ are the two olfactory areas, ley consist of thickened ectoderm, and are placed on the ventral aspect of e anterior cerebral vesicle, on either side of the mesial nasal process of the mto-nasal process, and on the cephalic side of the orifice of the stomodaeum ig. 54).

Each olfactory area soon becomes depressed and forms the olfactory pit. le depression is due to the growth of mesoderm; on the inner and outer sides is forms inner and outer nasal folds respectively, continuous in front but open hind. The outer fold is the longer, and the maxillary process, growing inards across this, comes into contact with the inner fold, with which it fuses, bus the pit becomes a shallow fossa. Its posterior end is closed by the junction maxillary and inner nasal processes, and the epithelial fusion between these akes the hucco-nasal membrane, separating it from the mouth. The membrane oses what is, potentially, a primitive posterior naris ; it is stretched as this ■ows, and finally breaks and disappears. .

The subsequent development of the proportionately full-sized cavity from tis small beginning has been described on p. 85, etc., to which the reader is


ferred. . .

The lower conchal mass is present at an early stage, being made by the mmal projection of the lower edge of the outer nasal fold. It is added to by idition of maxillary mesoderm as the fossa increases in length backwards, le middle and upper nasal conchce become evident later as the cavity grows ey are present by the end of the second month. The upper mass is described derived from the upper part of the inner wall, migrating across the roof, ie ontogenetic evidence of this is very doubtful. The cartilaginous bases of ie masses are derived from the cartilaginous capsule. In foetal life there is marked tendency for the two upper masses to show longitudinal subdivisions, ving the appearance of the presence of half a dozen or more conchae, but the Dpearance is deceptive, as these are only surface formations, and are usua y

st by the time of birth. . , „ ,

The maxillary sinus can be recognized in the third month as a depression l the outer wall. It extends very slowly, so that at birth it only makes a ivity a few millimetres wide in the inner part of the maxilla.

A cartilaginous nasal capsule is built Up round the two cavities as t ey ctend up. It is deficient below, where the elongated aperture is placed, e s lateral plate has its lower edge turned in to make the cartilaginous asis o ie lower nasal concha. The other nasal conchae are based on ingrowths from s inner aspect. It presents the septal cartilage centrally, forme m e 1C lesoderm between the two cavities. The vomer develops as a paire ossi ca on in the mesoderm along the lower or free edge of the septal cartilage.


1364


A MANUAL OF ANATOMY


palatine bone ossifies on the deep surface of the capsule, and the maxilla structures superficially. The premaxilla and incisive part of the palate devel in the region of the primitive palate. The capsule is in contact with the bo of the sphenoid above and behind, and a wing-like process here, the orbi sphenoidal process, is related with the lesser wing.


Fig. 827.


The two upper figures show the lower aspects of the projecting heads of embry of 4 mm. and 7 mm. (From reconstruction models.) The change position of the olfactory region is due to the growth of the telencephah in the 7 mm. specimen. This not only advances the front of the he; beyond the site of the olfactory fields, but also, as a result of increase breadth, turns them more on to the lower aspect. A and B in the low figures are sections through the olfactory fields of the two embryos, showii formation of olfactory pits and fronto-nasal process. C and D are diagrar rnatic sections to illustrate the further changes. The maxillary process are indicated by interrupted lines to show where they will come into po: tion, as in D. ONF, INF, lateral and medial nasal folds; FNP, fronto-nas process.

The Paranasal Sinuses. —The frontal, ethmoidal, sphenoidal, and maxilla! sinuses are developed as evaginations of the nasal mucous membrane, whi( extend into spaces formed by absorption within the respective bones. The ma toid air-cells are developed as evaginations of the tympanic mucous membran which is continuous with the nasal mucous membrane through the pharyngt tympanic tube and nasal part of the pharynx.

Olfactory Organ. —The true olfactory organ is situated in the upper par or olfactory region, of each nasal cavity. The olfactory epithelium, which cove:




THE HEAD AND NECK 1365

ie mucous membrane of this region, is developed from the upper part of the orresponding olfactory pit.

External Nose. —The dorsum and tip of the nose, and the columna nasi, are eveloped from the portion of the mesial nasal process which lies between the lobular processes. The upper and lower nasal cartilages are derived from the irtilaginous core of the corresponding lateral nasal process. The anterior asal aperture of each side represents, as stated, the external orifice of the



Fig. 828. —Antero-posterior Sections of Heads of Embryos of

16 and 28 Mm.


corresponding olfactory pit, but it is modified by secondary extensions of maxillary mesoderm round its margins.

The Vomero-nasal Organ (Organ of Jacobson). —The vomero-nasal organ is rudimentary in man, but is well developed in reptiles.* It takes the form of a blind pouch, which is situated in the lower and anterior part of the nasal septum on either side. The minute orifice

  • There is some doubt as to whether the rudimentary structure of man is

really vestigial of that of the lower forms.



















1366


A MANUAL OF ANATOMY


of the pouch lies above the recess or depression of mucous membrane which projects slightly into the upper end of the incisive canal. Th pouch extends upwards and backwards in the nasal septum for a ver short distance, and ends in a blind extremity. The vomero-nas; (subvomerine) cartilage lies underneath it. The vomero-nasal orga does not seem to perform any function in man. In those animal: however, in which it is well developed it receives two nerves, one c which is olfactory, the other being derived from the spheno-palatiu ganglion. Moreover, its epithelial lining is similar to that of the o factory region of the nasal cavity, inasmuch as it contains olfactor cells, the deep poles of which are continuous with olfactory filaments In such animals it acts as a supplementary organ of smell.


Fig. 829.—View, from below and behind, of the Roof of the Mouth of an Embryo of 16 Mm. (Sixth Week).

Showing the palate folds reaching the fronto-nasal process, the evident shaj of this process, though covered by a layer of maxillary mesoderm, and tl growth of the labial extension of the mesoderm, only just meeting its fello in the middle line. This will become much thicker and vertically deepe hiding the fronto-nasal form altogether. The interrupted lines indicathe extension upward of the upper level of the posterior nasal apertures.

Development of the Vomero-nasal Organ. —This organ is developed as diverticulum of a portion of the ectoderm of the olfactory pit. The diverticulu: projects upwards and backwards into a recess situated laterally within tl lower and anterior part of the septal nasal cartilage just above the upper er of the incisive canal; it marks the meeting of the paraxial and visceral mesodern in the septum.

The Pharynx.

The pharynx is situated behind the posterior nasal apertures, tl oropharyngeal isthmus, and larynx, and it extends from the basik region of the base of the skull to the level of the lower border of tl cricoid cartilage of the larynx, where it becomes continuous with tl oesophagus. It is a musculo-aponeurotic tube about 5 inches lon| and it attains its greatest width between the base of the skull an



THE HEAD AND NECK


1367


e hyoid bone. Below the latter level it narrows, and is flattened )m before backwards, so as to assume the form of a transverse cleft, cept during the act of deglutition.

Relations. —Posteriorly it rests upon the bodies and discs of the rvical vertebrae as low as the sixth, and the prevertebral muscles vered by the prevertebral fascia. Between it and the last-named scia is the retropharyngeal space, which is occupied by connective ssue, but this is so loosely arranged that no obstacle is offered to Le movement of the tube, and a post-pharyngeal abscess can readily ffuse itself. Anteriorly it communicates with (1) the nasal cavities trough the posterior nasal apertures, (2) the pharyngo-tympanic


Sinus of Morgagni


Lateral Pterygoid Muscle Styloid Process


Superior Constrictor - .4 _ Muscle


Middle Constrictor Muscle


Inferior Constrictor Muscle


--Head of Mandible

-Spheno-mandibu lar Ligament

.Ramus of Mandible

_,Stylo-phar. Muse.

.Stylo-hyoid Lig.

f_Medial Pterygoid

Muscle

__.Greater Horn of

Hyoid Bone

-’Angle of Mandible

Ah--- .-Median Pharyngeal

Ms Raphe


Fig. 830.


Oesophagus


-The Posterior Wall of the Pharynx and Adjacent

Structures.


ubes, (3) the buccal cavity through the oropharyngeal isthmus, and 4) the larynx. On this aspect its attachments are effected by means )f the constrictor muscles in its walls. Laterally it is related to the irincipal bloodvessels and nerves of the neck, and comes into contact vith the styloid muscles and the process from which they arise. Superiorly it is attached to the basilar region of the base of the skull.

r nferiorly it is continuous with the oesophagus. .

The wall of the pharynx consists of the following four strata,

rom without inwards: (1) the pharyngeal portion of the buccopharyngeal fascia, (2) the muscular coat, (3) the pharyngo-basi ar
ascia, and (4) the mucous coat.








1368


A MANUAL OF ANATOMY


Bucco-pharyngeal Fascia.—This is an offshoot of the prevertebrs layer of the deep cervical fascia along the medial aspect of the carotii sheath. In front it becomes continuous with the fascia covering th buccinator muscle. In association with this fascial stratum there ar many veins upon the posterior and lateral walls of the pharynx, whicl constitute the pharyngeal venous plexus.

Muscular Coat.—This is composed on either side of the three cou strictor muscles—inferior, middle, and superior—the stylo-pharyngeus

and the palato-pharyngeus (including th salpingo-pharyngeus).

Inferior Constrictor— Origin .—(i) The sid of the cricoid cartilage at its posterior part (2) the inferior horn of the thyroid cartilage and (3) the outer surface of the lamin behind the oblique line.

Insertion .—The median raphe on the pos terior wall of the pharynx, where it meet its fellow of the opposite side.

The lower fibres of the muscle are hori zontal, but the upper fibres pass upward and backwards more and more obliquel} and the highest fibres of the two muscle meet in the raphe to form a peak, which i about an inch below the basilar part of th occipital bone. The lower border of th muscle overlaps the upper end of the oesc phagus. The recurrent laryngeal nerve an inferior laryngeal artery pass upwards be


Fig. 831.—Scheme to show neath the lower border behind the cricc


Planes in Composition of Pharyngeal Wall, with Relation of Mus

SUP., MID., INF., upper, middle, and lower constrictors. Sinus of Morgagni is the interval be


thyroid joint. The upper border, which i very oblique, overlaps the lower portion c cles to Mucous Mem- the middle constrictor, and the interne brane (Dotted Line). laryngeal nerve and the superior laryngee

artery, on their way to pierce the thyro-hyoi membrane, pass between the two muscle anteriorly.

, . . . Middle Constrictor— Origin. —(1) The oute

and Skull base; the tube border of the greater horn of the hyoid bon is seen coming through over its entire length, (2) the lesser horr this. and (3) the hyoid extremity of the style

hyoid ligament.

Insertion .—The median raphe on the posterior wall of the pharym where it meets its fellow of the opposite side.

The muscle is fan-shaped, and its fibres consequently diverg very much as they pass round to reach the raphe. The inferior fibre descend very obliquely, and are overlapped by the upper fibres c the inferior constrictor, the internal pharyngeal nerve and superic laryngeal artery passing to the thyro-hyoid membrane between th




THE HEAD AND NECK


1369


0 muscles anteriorly. The middle fibres pass more or less transrsely. The superior fibres ascend obliquely, and reach the basilar rt of the occipital bone. They overlap the lower portion of the perior constrictor, and the stylo-pharyngeus muscle and glossoaryngeal nerve pass between the two. The lingual artery lies perficial to the muscle at the greater horn of the hyoid bone.

Superior Constrictor— Origin. —(1) The lower third of the posterior rder of the medial pterygoid plate, and the pterygoid hamulus ocess of the sphenoid bone; (2) the posterior aspect of the pterygo


Fig. 832. _Dissection showing the Cheek, Pharynx, Submandibular

Region, and Larynx (Right View).

landibular ligament, along which it meets the buccinator muscle, ]) the posterior extremity of the mylo-hyoid line of t e mandibe, I-) the mucous membrane of the mouth; and (5) the side o e ongue.

Insertion .—The median raphe on the posterior wall of the pharynx diere it meets its fellow of the opposite side. A few °f t e ig es bres are inserted into the pharyngeal tubercle on the under sur ace

f the basilar part of the occipital bone. .

The muscle is four-sided. The fibres for the most part pass horiontally, but the lower fibres radiate in a downward direction, whi st he upper fibres curve backwards and upwards. The lower portion





1370


A MANUAL OF ANATOMY


of the muscle is overlapped by the upper part of the middle constricto the stylo-pharyngeus muscle and glosso-pharyngeal nerve passir between the two. Between the upper, concave border and the bas of the skull there is an interval occupied by the pharyngo-basik fascia, which is here stronger than elsewhere, and so compensates f( the absence of muscular fibres. This interval is semilunar, and known as the sinus of Morgagni.

Nerve-supply of the Constrictor Muscles.—The nerves are derive from the pharyngeal plexus, which is formed by the pharyngeal branc


Fig. 833. —Sagittal Section through the Nasal Cavity, Mouth, Pharynx, (Esophagus, and Larynx.

The outer wall of the right nasal cavity is shown.


of the vagus, the pharyngeal branches of the glosso-pharyngeal, an sympathetic filaments. The motor fibres of the plexus are derive from the pharyngeal branch of the vagus, but their ultimate source i the cranial root of the accessory nerve. The inferior constrictor musd also receives twigs from (1) the external laryngeal branch of tb superior laryngeal nerve, and (2) the recurrent laryngeal nerve as i passes beneath the lower border of the muscle.

Action.—The constrictor muscles are concerned in the act of d( glutition. The superior constrictor and upper portion of the midd] constrictor act upon the nasal part of the pharynx—that is, the con













THE HEAD AND NECK


I 37 i


irtment of the pharynx which lies above the soft palate—and is in mmunication with the nasal cavities through the posterior nasal jertures. They narrow the nasal part of the pharynx in the lateral rection, and this movement, in conjunction with the action of the ilato-pharyngeal arch, shuts off the cavities, thus preventing relrgitation into and through the nasal cavities. The lower portion of ie middle constrictor and the inferior constrictor diminish the calibre the oral part of the pharynx. Coming into action during the second age of deglutition, they grasp the bolus of food and press it downwards to the oesophagus. The constrictor muscles contract rapidly, and order from above downwards.

For a description of the stylo-pharyngeus and palato-pharyngeus uscles (including the salpingo-pharyngeus), see pp. 1323 and 1352.

Pharyngo-basilar Fascia (Pharyngeal Aponeurosis).—This is situated Tween the muscular coat and the mucosa. Interiorly it is weak and distinct, but superiorly it acquires greater firmness and density, specially where it is attached to the basi-occipital, the apex of the strous part of the temporal bone, the adjacent portion of the pharyngounpanic tube, and the medial pterygoid plate of the sphenoid bone.

receives an accession of strength in the median line from a strong

imdle of fibres which descends from the pharyngeal tubercle on the nder surface of the basilar process of the occipital bone, and which irms the raphe of the pharynx.

Interior of the Pharynx.—The mucous membrane, which forms ie deepest stratum in the pharyngeal wall, is of a papillary laracter, and has the following important continuations: (1) with ie mucous membrane of the pharyngo-tympanic tube, and thence ith that of the tympanic cavity; (2) with that of the nasal cavities irough the posterior nares; (3) with that of the cavity of the mouth irough the oropharyngeal isthmus; (4) with that of the larynx through ie superior laryngeal aperture; and (5) with that of the oesophagus, d its upper and back part it is richly provided with lymphoid tissue, i be noticed presently, and in the submucous tissue there are many cinous glands of a mucous character.

The soft palate projects into the cavity of the pharynx in a downward and backward direction, and divides it into two regions, upper nd lower. The upper region is known as the nasal part of the pharynx, nd is in communication with the nasal cavities and pharyngo-tympanic iibes. It also communicates with the lower region. by means of tie pharyngeal isthmus. The lower region is subdivided into two arts, oral and laryngeal. The buccal part is limited above by the 3 ft palate, and below by the inlet of the larynx, and it communicates dth the cavity of the mouth through the oropharyngeal isthmus, he laryngeal part is situated behind the larynx, with which it ommunicates, as well as with the oesophagus interiorly.

The Nasal Part of the Pharynx.—This is entirely respiratory in motion, and is therefore always patent. It measures a little more fan an inch from above downward, and about 2 inches from side to


^372


A MANUAL OF ANATOMY


side, while from before backward it is about f inch. It is bounded front by the posterior nasal apertures and the posterior border of t] vomer; behind, by the vertebral column; above, by the basilar pa of the occipital and part of the body of the sphenoid; and below 1 the soft palate, which can be elevated and depressed. Four openin communicate with it. The anterior wall has the oval openings the posterior nasal apertures leading from the nasal cavities, ai separated from each other by the posterior border of the vomer. Ea< opening in the recent state measures about i inch from above dow wards, and about \ inch from side to side. Through it, on the out wall of the corresponding nasal cavity, are seen the posterior par


Posterior Border of the Vomer


Tubal Elevation


Right Posterior Nasal Aperture / Levator Palati


Salpingo pharyngeus


Musculus Uvulas Palatopharyngeus


1 WL— . Tensor Palati


- Medial Pterygoid Uvula

- Root of Tongue


-pL -Epiglottis

_ Wall of Pharynx

_ Pyriform Fossa .. Arytenoideus Obliquus . Arytenoideus Transversus

A Crico-arytenoideus Posterior


CEsophagus


Fig. 834.—The Pharynx opened from Behind.

of the middle and inferior nasal conchae, covered by mucous membram and above and below the inferior nasal concha are seen the posteri( parts of the middle and inferior meatus. The orifice of the pharyng' tympanic tube is situated on each lateral wall behind and external 1 the corresponding posterior nasal aperture, and on the same lev as the posterior end of the inferior nasal concha. It is somewhc triangular, and has, above and behind, a prominent round bordf formed of cartilage covered by lymphoid tissue, called the tub . elevation. Behind the tubal elevation there is a deep pouch on tl lateral wall of the nasal part of the pharynx, called the pharynge recess (fossa of Rosenmuller), which is a secondary widening of til











THE HEAD AND NECK


1373


of of the primitive pharynx. The mucous membrane extending

tween the pharyngeal recesses at the upper and back part has a

imber of folds containing a large amount of lymphoid tissue, which institute the naso-pharyngeal tonsil. When enlarged, this mass is ible to obstruct the orifices of the pharyngo-tympanic tubes, and ten the posterior nasal apertures, and is known as adenoids. At le lower part of the naso-pharyngeal tonsil there may be seen a small edian recess, called the pharyngeal bursa, which leads upwards and ickwards towards the pharnygeal tubercle on the basilar part of the xipital bone.

The mucous membrane is covered by ciliated columnar epithelium.

The Oral Part of the Pharynx.—This part is situated between the )ft palate and the inlet of the larynx. Anteriorly it communicates ith the cavity of the mouth, through the oropharyngeal isthmus, elow which the root of the tongue forms its anterior wall. Each iteral wall shows the palato-pharyngeal arch, the interval between le two arches corresponding to the pharyngeal isthmus. In front E each arch is a triangular depression which lodges the tonsil.

Laryngeal Part of the Pharynx.—This part is situated behind the trynx. Anterior to it there are the epiglottis, the inlet of the larynx, n either side of which is a recess called the pyriform fossa, and the osterior parts to the arytenoid and cricoid cartilages, with the muscles dated to them. It communicates with the larynx anteriorly and tie oesophagus interiorly.

The mucous membrane of the buccal and laryngeal portions is Dvered by stratified squamous epithelium.

Blood-supply.—The arteries of the pharynx are derived from the scending pharyngeal branch of the external carotid, the ascending alatine and tonsillar branches of the cervical part of the facial artery, nd the greater palatine and pharyngeal branches of the maxillary.

The veins form a copious pharyngeal plexus, which is disposed pon the lateral and posterior walls of the pharynx. It communicates uperiorly with the pterygoid venous plexus, and receives tributaries 'om the soft palate, tonsils, and pharyngo-tympanic tubes. Interiorly tie blood is conveyed from it into the internal jugular vein.

Lymphatics.—The lymphatic vessels from the upper part of the harynx pass to the deep facial lymph glands, which are associated rith the lateral walls of the tube, and those from the remaining part ass to the upper group of deep cervical lymph glands. Some of the ^mphatics from the upper part pass to the retropharyngeal lymph lands of its own side, each of which lies upon the upper part of the orresponding longus capitis muscle.

development of the Pharynx and of the Pharyngeal Pouches or Visceral Grooves

and Visceral Arches (see Chapter II.).

The pharynx is developed from the anterior or cephalic part of the fore-gut.

On the ventral wall or floor of this part certain grooves are found at an arly stage running more or less transversely, and separated from one another •y thick and transversely directed masses of mesoderm; these are the visceral


1374


A MANUAL OF ANATOMY


arches, and the grooves are known as visceral grooves (clefts). Each groo\ runs out to the lateral part of the cavity, where it terminates in a deepe pharyngeal pouch, which can again be divided into dorsal and ventral part: each of these being the seat of distinct developments. On the outer aspect < the embryo the arches are visible, except in the case of the fifth and sixth, an the external grooves between them, lined with ectoderm, are at first in conta( with the entodermal linings of the corresponding lateral pharyngeal pouche: This contact is soon lost, save in the case of the first (external meatus).

As growth proceeds, the arches (and grooves) are placed (see Fig. 835) moi obliquely as they are followed back. They run medially into a central long tudinal prominence, the hypobranchial eminence, especially in the case of tt


Fig. 835.—A, external pharyngeal arches, 4 mm. B, floor of early pharyn exposed from above. C, shows on left the adult formations, their arc! origins being indicated on right. D, indicates remnants of skeletal structure of arches. Visceral arches are numbered in Roman figures. M, R, Meckel and Reichert's bars. On left, in C, the forward growth of third arch : shown not only in tubo-tympanic part, but in back of tongue, across tonsi fossa, and in pharyngeal extension to palate.

third and fourth, and in front of this is the little tuberculum impar, centrall placed in the first groove. The opening of the pulmonary outgrowth is sagittall placed just behind the eminence.

The arches and grooves are numbered from before backwards, the numbe of each groove being that of the arch just in front of it. The first is often terme the mandibular arch, as the lower jaw forms in it; its upper and outer part lie under the head region in front of the ear, and from here a maxillary proC6£ grows forwards from it below the eye to form the upper arcade of the mouth, There are,six arches and five grooves. The first four arches are distinc (see Fig. 49A). The fifth is rudimentary, and is buried with its groove at the bottoy of the fourth pouch. The sixth forms the immediate boundary on each sid of the pulmonary opening. The first four grooves are distinct, the fifth i







THE HEAD AND NECK 1375

uded in the fourth, and no definite groove limits the caudal part of the th arch.

The widest part of the cavity is opposite the second arch. Here is formed ! tubo-tympanic recess from which the tympanic cavity and tube are differentid as the result of forward growth of the third arch over the second. This wth goes over the region of the large second lateral pouch, but leaves the sal or outer part of this in the tympanic cavity, while its ventral part remains the pharyngeal wall and becomes the fossa in which the tonsil will develop, e growth forward of the third arch comes up against the first arch to some

ent, and obliterates its groove so far, but the dorsal part of the first pouch

aains in the tympanic cavity (Fig. 835, C).

The hypobranchial eminence forms the main epiglottic mass; the third arch ning from this becomes the pharyngo-epiglotiic fold, and the fourth forms s ary-epiglottic fold. The third pouch marks the pyriform fossa, while the irth is lost, occasionally indicated as a depression beside the lower margin the cricoid. The sixth arches are joined with an upward growth of the fourth form a paired mass standing up behind the epiglottis; this mass (arytenoid inences) is separated from the epiglottis by a transversely disposed cleft, bounded erally by the ary-epiglottic folds, and hides the sagittal opening from view d makes the supraglottic part of the larynx. The tongue is developed in front the hypobranchial eminence, the tuberculum impar being enlarged to form 5 front part of the organ, while paired growths from the front of the eminence d (?) the central parts of the second arches make its back part behind the bus terminalis.

The ventral part of the third pouch gives origin to the bud from which the miUS is formed. A similar bud from the fourth pouch develops into an ithelial mass embedded in the back of the lobe of the thyroid. The thyroid md proper is formed from a central entodermal downgrowth which takes ice early just behind the tuberculum impar; the situation of this is therefore irked in the adult by the foramen caecum, which is formed by the two masses at make the back of the tongue meeting each other at an angle, and being us applied to the front portion of the organ.

The third pouch and the constituents of the fourth pouch complex give off rtain outgrowths which separate from them through atrophy of the pharynal connection, and which may be divided into dorsal and ventral bodies. Ventral dies from the third pouch make the thymus, shifting caudally; from the irth, make a ‘ rudimentary thymus 5 which remains applied to. the back of e thyroid lobe; from the fifth rudiment, constitute an ‘ ultimo-branchial dy’ which remains in the same situation. Dorsal bodies: from the third, e lower parathyroid, carried down with the thymus; from the fourth, upper rathyroid, remaining more or less in situ ; no dorsal body from the fifth has t been found in human embryos.

At a later stage each visceral arch presents the following four elements:

) an artery; (2) a visceral myotome or muscle-segment; (3) a nerve (or nerves); d (4) a rod of cartilage. The artery is known as a visceral arch artery, and it one of the primitive aortic arches, establishing communications between the rresponding primitive ventral and dorsal aortas.

Myotomes of Visceral Arches. —The visceral myotome in each arch gives rise certain muscles. The myotome of the first arch furnishes (1) the. anterior lly of the digastric ; (2) the mylo-hyoid; and (3) the muscles of mastication— tmely, (a) masseter, ( b ) temporalis, (c) lateral pterygoid, and (d) medial pterygoid.

The myotome of the second arch furnishes (1) the posterior belly of the digastric; ) the stylo-hyoid; and (3) the stapedius. From this myotome are also derived .e muscles Of expression on the face and epicranial region, as well as the platysma. iese muscles migrate during ontogeny over the neighbouring areas.

The myotome of the third arch furnishes the stylo-pharyngeus, and the middle •nstrictor of the pharynx may be regarded as derived from it.

The myotome of the fourth arch (and perhaps that of the fifth arch) may be garded as furnishing the inferior constrictor of the pharynx.


A MANUAL OF ANATOMY


1376

Nerves of Visceral Arches—First or Mandibular (Oral) Arch. —The comm

nerve of this arch is the trigeminal nerve. The mandibular division belongs the mandibular process of the arch, and to its muscles, and the lower teeth one side; the maxillary division belongs to the maxillary process of the arch, a to the upper teeth of one side. The ophthalmic division is not concerned in i supply of the arch; it is a distinct nerve phylogenetically, only supplying parax formations.

Second or Hyoid Arch. —The nerve of this arch and of the first pharyng( pouch is the facial nerve. The auditory nerve may be included.

Third or Thyro-hyoid Arch. — The nerve of this arch and of the secoi pharyngeal pouch is the glosso-pharyngeal nerve.

Fourth Arch. —The nerve of this arch is the superior laryngeal nerve, whi is a branch of the vagus.

Sixth Arch. —The nerve of this arch is the recurrent laryngeal nerve, which a branch of the vagus.

The bar of cartilage in each arch is developed in the mesenchyme, whi forms the core of the arch.

Metamorphoses of the Visceral Arches.

First Visceral or Mandibular Arch. —This arch is situated, as stated, betwe the first pharyngeal pouch and the stomodaeum or primitive oral cavity. ] artery is the first primitive aortic arch; its nerve is the mandibular divisi of the trigeminal nerve; its cartilaginous bar is known as Meckel’s cartilage. T ventral end of this cartilage meets its fellow of the opposite side, and is join to it by connective tissue. The dorsal end is related to the periotic cartilagino capsule, and furnishes an offshoot, called the manubrium.

1. The upper or dorsal end of Meckel’s cartilage, becoming ossified, grv rise to the malleus, and probably the incus.

2. The lower or ventral end of Meckel’s cartilage is ossified in the incis portion of the mandible.

3. The part of Meckel’s cartilage between the upper and lower ends disappea: The membranous investment of the lower or mandibular portion of this part grv rise to the chief part of one-half of the body of the mandible, and the lower h of the ramus as high as the mandibular foramen. The membranous investme of the upper portion, between the periotic cartilaginous capsule and the mandibul foramen, forms the spheno-mandibular ligament.

4. The maxillary process, aided by part of the fronto-nasal process —namel the globular and lateral nasal processes —gives rise to the maxilla (see Develo ment of the Skull).

5- The upper end of the first arch on its superficial surface gives rise to t tragus, and part of the helix of the pinna.

Second or Hyoid Arch. —This arch is situated, as stated, between the fii and second pharyngeal pouches. Its artery is the second primitive aortic arcl its nerve is the facial nerve, with the chorda tympani; and its cartilaginous b is called the hyoid bar, or cartilage of Reichert. This bar ventrally is connect with its fellow of the opposite side by a transverse copula, forming part of t body of the hyoid bone.

The second bar becomes transformed into the following structures:

1. The upper or dorsal segment of the hyoid bar gives rise to the head, net and limbs of the stapes, the foot-piece of that ossicle perhaps being develop* from the cartilaginous capsule of the labyrinth within the fenestra vestibuli.

2. The succeeding segment of the hyoid bar gives rise to (a) the tympar hyal, and (b) the stylo-hyal, which collectively constitute the styloid process the temporal bone.

3. The next portion of the hyoid bar becomes converted into fibrous tissr and forms the stylo-hyoid ligament, which sometimes exists as an epi-hyal born

4. The lower or ventral segment of the hyoid bar gives rise to the cerato-hyt or lesser horn of the hyoid bone.


THE HEAD AND NECK


1377


The second, arch also gives rise superiorly to the antihelix, antitragus , and ule of the pinna; and inferiorly, along with the third arch, possibly helps to

m one-half of the posterior third of the tongue.

Third or Thyro-hyoid Arch— This arch is situated between the second and rd pharyngeal pouches. Its artery is the third primitive aortic arch; its nerve

he glosso-pharyngeal nerve; and its cartilaginous bar is known as the thyro)id bar. This bar is connected ventrally with its fellow by a copula.

A large portion of the thyro-hyoid bar disappears, but its lower or ventral ment gives rise to the thyro-hyal or greater horn of the hyoid bone. The i-hyal or body of the hyoid bone is developed from the copula.

Fourth and Fifth Visceral Arches. —The artery of the fourth arch is the fourth mitive aortic arch, and its nerve is the superior laryngeal nerve, which is a ,nch of the vagus. The artery of the fifth arch is the fifth primitive aortic h, and its nerve a small and transient branch of the vagus. The greater •tions of these two arches disappear; but the lower or ventral ends of their tilaginous bars are by some regarded as giving rise to a small part of the lina of the thyroid cartilage. The lower musculature of the pharynx comes m the cells of the fourth arch, as does also the crico-thyroid .

Sixth Visceral Arch. —The artery of this arch is the sixth primitive aortic h. Its nerve is the recurrent laryngeal. The sixth arch itself, being unferentiated, leaves no traces behind it, but the internal intrinsic muscles of ! larynx are formed from its cells.

The metamorphoses of the pharyngeal pouches have been already described connection with these pouches.

The first external furrow, corresponding to the first internal pharyngeal ich, gives rise, as stated, to the external auditory meatus, and the walls of

upper part of this furrow become differentiated into the component parts

the pinna.

Sinus Cervicalis and Cervical Fistula. —The first or mandibular and second hyoid arches increase more rapidly in all directions than the succeeding hes. The third and fourth visceral arches therefore become overlapped the second or hyoid arch, and now lie at the bottom of a depression. This Dression is called the sinus cervicalis. The lining membrane of the sinus is med by the ectodermic coverings of the overlapped visceral arches. The us is, as a rule, transitory, the second arch atrophying rapidly, and the rd external groove disappearing, while the third arch flattens. The fourth

h is partly covered from behind, a ‘ placodal duct ' being enclosed for a short

le. Otherwise there is no ‘ closing of a cervical sinus ’ in man such as has m described in lower forms.

Morphology of the Visceral Arches and Clefts.— In aquatic animals — e.g., ihes and Amphibia at an early stage, but only in Perennibranchiata pernentlv—these are called the branchial or gill-arches and clefts. The clefts lge in number from five to eight, and they differ from those of Mammals I Birds, inasmuch as they are complete clefts, the closing membrane being sent. They therefore establish free communications between the exterior 1 the fore-part of the alimentary canal, or throat, for the entrance and exit water.

The functional branchial arches are those which are post-oral, commencing

h the second. The second branchial or gill-arch is not, however, a real

tnchial arch in the functional sense, but is opercular, giving rise on either e to the operculum or gill-cover. The real branchial or gill-arches, properly called functionally, are those which succeed to the second, of which the third 1 fourth are conspicuous. I he mucous membrane of the real branchial -hes is folded into parallel lamellae, which are placed close together, and s freely furnished with capillary bloodvessels, the blood being derived from ^ branchial-arch arteries. These lamellae constitute the branchiae or gills. Aquatic respiration consists in the passage of currents of water containing pgen through the complete gill-clefts into the pharyngeal part of the foret. As the water bathes the branchiae, or gills, its oxygen is taken up into the

87


A MANUAL OF ANATOMY


1378

blood within the branchial capillaries, and the carbon dioxide of the capillc blood is yielded up to the water. Thereafter the water is expelled throu the gill-clefts, and is immediately replaced by a fresh current of respiratc water. The branchiae, or gills, of aquatic animals therefore correspond functi( ally to the lungs of Mammals and Birds, whose respiration is aerial.

The Pharyngo-tympanic Tube.

The pharyngo-tympanic tube (Eustachian tube) leads from t tympanic cavity to the nasal part of the pharynx, and is about i| inct in length. It is directed forwards, inwards, and slightly downwan and is composed of two parts, bony and cartilaginous. The bo or postero-lateral part is about \ inch long, and is situated in the anj between the petrous and squamous parts of the temporal bone. T cartilaginous or antero-medial part is about 1 inch in length, and 1 on the groove between the greater wing of the sphenoid and the api< portion of the petrous part of the temporal bone. It is at first narro but gradually enlarges, so as to resemble a trumpet. The narrow( part of the whole tube is at the junction of the bony and cartilaginc parts; this is the isthmus, and the widest part is at the pharyng< orifice. The roof, inner wall, and upper part of the outer wall of t cartilaginous part consist of a triangular plate of cartilage, the margi of which are slightly rolled towards each other. The floor and mt of the outer wall are formed of a dense fibrous membrane. T pharyngeal orifice of the tube is expanded, and is situated on the late: wall of the nasal part of the pharynx behind, and external to, t corresponding posterior nasal aperture, and on the same level as t posterior end of the inferior nasal concha. It is somewhat triangul; and above and behind is the tubal elevation, already described, form by the thick margin of the cartilage, and posterior to this is the phar) geal recess.

The tube is lined with mucous membrane, which is continue with that of the tympanic cavity on the one hand, and of the na part of the pharynx on the other. It is thin in the bony part of t tube, but in the cartilaginous part it is thick, and contains mucc glands and lymphoid tissue. It is covered by stratified columr ciliated epithelium.

Muscles connected with the Pharyngo-tympanic Tube. —The leva palati has an origin from the lower margin of the cartilage of the tul the tensor palati from the outer side of the cartilage, and the salpinj pharyngeus is attached to the lower and front part of the tube. Duri deglutition the orifice of the tube is opened.

Arteries are derived from the artery of the pterygoid canal, fr( the third part of the maxillary, and the ascending pharyngeal bran of the external carotid.

Nerves. —The nerves come from the tympanic plexus on the ini wall of the tympanic cavity, and the nerve of the pterygoid canal.

Development. —From the tubo-tympanic recess of the primitive phary modified and narrowed by forward growth of the third arch (Fig. 835, C).


THE HEAD AND NECK


1379


The Larynx.

The larynx is the upper part of the respiratory passage, being )dified in structure so as to enable it to act as the organ of voice, is situated in the median line of the neck above the trachea, and it s opposite the fourth, fifth, and sixth cervical vertebrae. Superiorly opens into the laryngeal portion of the pharynx, and interiorly into e trachea. It is covered in front by the integument and the deep rvical fascia, and the laryngeal portion of the pharynx lies behind On either side it is in relation with the upper part of the lobe the thyroid gland, the sterno-hyoid, omo-hyoid, sterno-thyroid, d thyro-hyoid muscles, and the common carotid artery.


Epiglottis

Superior Horn of Thyroid . —

Cartilage / .

Cuneiform Cartilage _i_ Comiculate Cartilage !j—


Axytenoideus Obliquus — Arytenoideus Transversus--'

Crico-arytenoideus Posterior Crico-thyroid Joint


Cricoid Cartilage—— " Trachea


Wu>. •••


SEI!

ll '!)

f 1 »•

tail,

(1 Ml

‘lull


?ig. 836. —The Intrinsic Muscles of the Larynx (Posterior View).


Structure.—The larynx consists of a framework of cartilages, some which are connected by joints and ligaments; it is provided with ecial muscles, spoken of as intrinsic ; and it is lined with mucous embrane.

Cartilages are nine in number, three being single and three arranged pairs. The single cartilages are The epiglottis, the thyroid, and the icoid; and the three arranged in pairs are the arytenoid, corniculate, id the cuneiform.

The epiglottis is a leaf-like plate of yellow elastic fibro-cartilage, tiich is placed between the base of the tongue and the inlet of the rynx. Its lower part forms a stalk which is attached to the receding igle of the thyroid cartilage, just below the thyroid notch on its







1380


A MANUAL OF ANATOMY


upper border, by means of a fibro-elastic band, called the thyr epiglottic ligament. Above it has a broad, round, free margin. Ea< lateral border is free above, but its lower part is contained within t] ary-epiglottic fold of mucous membrane. The anterior or lingu surface is free over its upper part, where it faces the base of the tongr and is covered by mucous membrane. This membrane is prolong! on to the base of the tongue as the glosso-epiglottic fold, which medially placed. It is also prolonged from the sides of the epiglotl on to the lateral walls of the pharynx as the pharyngo-epiglottic fold On either side of the glosso-epiglottic fold, between it and each pharyng epiglottic fold, there is a depression or fossa, which is known as t] vallecula. Lower down than these folds the anterior surface is co nected to the back of the upper border of the body of the hyoid boi by an elastic, semilunar membrane, called the hyo-epiglottic ligamer


Thyroid Notch


- Superior Horn of Thyoid Cartilage

Superior Thyroid Tubercle

• Oblique Line of Lamina Laryngeal Prominence ' Inferior Thyroid Tubercle

' Inferior Horn


Cricoid Cartilage Crico-thyroid Ligament


Fig. 837.—The Thyroid and Cricoid Cartilages of the Larynx

(Anterior View).


Above the upper border of the thyroid cartilage the anterior surfa< is attached to the back of the body of the hyoid bone and of the thyr hyoid membrane by dense connective tissue. The posterior or lary geal surface is free over its whole extent, and is covered by mucoi membrane. It is concave from side to side, and concavo-convt from above downwards. The lower convexity forms the tuberc (cushion). When the mucous membrane is removed, the epiglott presents a number of small glandular pits.

Development.— The epiglottis is developed from the hinder part of the hyp branchial eminence.

Thyroid Cartilage. —This cartilage is composed of two flat quadi lateral laminae false), which meet in front by their anterior border but diverge widely behind. The angular projection formed by the union is called the laryngeal prominence (pomum Adami). The unic is confined to about the lower half of each anterior border, and the




THE HEAD AND NECK


1381

left superiorly a deep triangular cleft called the thyroid notch. The ►sterior border, of greater length than the anterior, is round, and yes attachment to fibres of the palato-pharyngeus and stylo-pharynus muscles. At either extremity it is prolonged into a projection, e superior horn and inferior horn respectively. The superior horn yes attachment to the lateral thyro-hyoid ligament, and the inferior irn, which is slightly incurved, is faceted on its inner aspect to ticulate with the cricoid cartilage. The superior border is for the ost part convex, and near its back part is a slight eminence, called e superior thyroid tubercle. The inferior border is almost horizontal, id has an eminence about the junction of the posterior third with the terior two-thirds, called the inferior thyroid tubercle. It gives tachment to the median portion of the crico-thyroid ligament and e crico-thyroid muscle. The outer surface of the lamina is marked


Laryngeal Prominence


Fig. 838.—The Thyroid and Cricoid Cartilages of the Larynx

(Lateral View).


an oblique line, which extends downwards and forwards from the perior to the inferior tubercle. This line gives insertion to the irno-thyroid, and origin to the thyro-hyoid muscles. It divides the ter surface into two unequal parts—an anterior three-fourths and posterior fourth, the latter giving origin to fibres of the inferior nstrictor muscle. The inner surface of the lamina is smooth, slightly ncave, and covered by mucous membrane. In the median line, hind the laryngeal prominence, there is a vertical depression known the receding angle. Beginning just below the thyroid notch on e upper border and passing downwards, this region gives attach^nt to the following structures: the thyro-epiglottic. ligament, the stibular ligaments, and the vocal ligaments, in association with which 5 the fibres of the thyro-arytenoid muscles.

Development of the Thyroid Cartilage. —The thyroid cartilage represents ' ventral portions of the skeletal cartilages of the fourth (and ? fifth) visceral lies of either side, which become united by a median plate.



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A MANUAL OF ANATOMY


Cricoid Cartilage.—The cricoid cartilage is situated below tl thyroid cartilage, and forms the lower part of the larynx. It bea some resemblance to a signet-ring, and it consists of two parts—s anterior arch and a posterior lamina.

The arch is narrow from above downwards as well as from sic to side. The inferior border is horizontal, and is connected with tl first ring of the trachea by a fibro-elastic membrane. The superi border is connected with the inferior border of thyroid cartilage t the crico-thyroid ligament.

The lamina is quadrilateral, broad, and deep. Its depth is owii to the rapid elevation of the superior border of the arch as it pass backwards. The inferior border is connected laterally with the fir

ring of the trachea by a fibro-elastic membran and medially, where the tracheal rings are d ficient, to the same membrane. The superi border has a median notch, and on either side «  this an oval convex facet for articulation wil the base of the arytenoid cartilage. The posteri surface is divided into two depressed areas by median vertical ridge, which gives attachment the longitudinal muscular fibres of the oesophagi! The depressed area on either side of this medic vertical ridge gives origin to the crico-arytenoidei posterior.

The outer surface of the cricoid cartilage pr sents posteriorly a circular facet for articulatic with the inferior horn of the lamina of the thyroid cartilage. Tl upper sloping border of this part gives attachment along its inn margin to the lateral portion of the crico-vocal membrane.

The internal surface of the cricoid cartilage is lined with the mucoi membrane of the larynx.

Development. —The cricoid cartilage, like the rings of the trachea, is develop! in the mesoderm of the respiratory tube, in the sixth arch.

Arytenoid Cartilages.—These cartilages are placed above the crico cartilage posteriorly. Each has the form of a three-sided pyrami and measures about -J inch in height, and about J inch in width the base. The apex looks upwards, and is curved in a backward at inward direction. It is surmounted by the corniculate cartilag The base looks downwards, and is slightly concave and faceted articulate with the superior border of the cricoid cartilage posteriori Two of the three angles of the base project. The anterior ang] somewhat pointed, is directed straight forwards to form the voc process. It gives attachment to the vocal ligament. The extern angle, thick and somewhat round, has an inclination backwards well as outwards, and is known as the muscular process. Anterior it gives insertion to the crico-arytenoideus lateralis, and posterior to the crico-arytenoideus posterior. The surfaces are antero-laten


For Articulation with Arytenoid Cartilage


Fig. 839.— The Cricoid Cartilage of the Larynx (Posterior View).



THE HEAD AND NECK


1383


sterior, and medial. The antero-lateral surface, a little above the cal process, attaches to the vestibular ligament, and above and

eral to the vocal process the thyro-arytenoideus muscle. The

sterior surface is triangular and concave, and gives attachment to portion of the arytenoideus transversus. The medial surface faces

fellow of the opposite side, and is covered by mucous membrane,

forms the posterior part of the lateral boundary of the rima glottidis. le borders are anterior, posterior, and lateral. The anterior border parates the medial from the antero-lateral surface, and terminates low in the vocal process. The posterior border separates the medial )m the posterior surface. The lateral border separates the antero-lateral )m the posterior surface, and ends below in the muscular process.

The thyroid and cricoid cartilages usually retain their cartilaginous con:ion up to about the twentieth year. In the case of the thyroid cartilage fification proceeds from the inferior horn, there being a special osseous nucleus the region of the laryngeal prominence.


Fig. 840. —The Right Arytenoid Cartilage and Corniculate Cartilage (Lateral Aspect Enlarged).

The anterior part and lower margin of the cricoid cartilage remain cartipnous for some time, but the remainder undergoes ossification simultaneously ith the thyroid cartilage.

Ossification of the arytenoid cartilages takes place at a later date than in e case of the two preceding cartilages.

Corniculate cartilages (cartilages of Santorini) are two small, somehat conical nodules of yellow elastic cartilage which cap the apical arts of the arytenoid cartilages, their direction being backwards and iwards. Each lies within the ary-epiglottic fold of mucous membrane.

Cuneiform cartilages are two nodules of yellow elastic cartilage, Inch are situated, one on either side, in the ary-epiglottic fold of iucous membrane at its back part, not far from the corniculate irtilages.

Development. —The arytenoid cartilages are formed in the sixth arches, id the ary-epiglottic folds from the fourth. The corniculate cartilages are I shoots of the arytenoid cartilages. The cuneiform cartilages are derived from

ie epiglottis.


1384


A MANUAL OF ANATOMY


Ligaments 0! the Larynx—Thyro-hyoid Membrane.—This is

broad membranous sheet, which passes between the superior borde of the thyroid cartilage and the back of the upper border of the bod of the hyoid bone, as well as the deep border of each greater horr Its central and lateral portions are strong, and are composed large! of elastic tissue. The central portion is known as the median thy re hyoid ligament, its lower attachment being to the border of the thyroii cartilage. The lateral portions, round and cord-like, are very elastic and are known as the lateral thyro-hyoid ligaments. Each extend from the superior horn of the thyroid cartilage to the tip of the greate horn of the hyoid bone, and enclosed within it, towards its upper pail there is a small nodule of cartilage called the cartilago triticea Between the upper median portion of the thyro-hyoid membrane ari( the concave posterior surface of the body of the hyoid bone there i a synovial bursa. It is to be noted that the superior attachment 0


the thyro-hyoid membrane is such as to enable the upper part of the thyroid cartilage, when raised, to be received within the outline 0: the hyoid bone. The central portion of the membrane is subcutaneous but on either side it is covered by the thyro-hyoid muscle. Beneatf the posterior border of this muscle the internal laryngeal nerve anc superior laryngeal artery pierce the membrane.

Crico-vocal Membrane.—This membrane is composed of an anterioi and two lateral portions. The anterior portion or crico-thyroid ligameni portion, elastic and triangular, is attached by its base to the lowei border of the thyroid, and by its apex to the upper border of the cricoid, close to the mid-line. It is subcutaneous in the median line except that it is crossed by the crico-thyroid branch of the superioi thyroid arteries. Through this portion laryngotomy may be performed. The lateral part of the crico-vocal membrane is connectec
















THE HEAD AND NECK


1385

elow with the upper border of the lateral part of the cricoid cartilage, uperiorly it is not connected with the thyroid cartilage, but passes eep to its lamina into the larynx, where it expands in an inward irection, and extends from the back of the lamina of the thyroid artilage in its lower part, close to the receding angle, to the under spect of the vocal process of the arytenoid cartilage. Between these oints it becomes continuous with the vocal ligament. The lateral ortion of the crico-thyroid membrane (within the lamina of the thyroid artilage) is covered by the crico-arytenoideus lateralis and thyrorytenoideus.

Vestibular Ligaments (Superior Thyro-arytenoid Ligaments).—These Drm two small fibrous bands, one at either side, which lie within the dds of mucous membrane, called the vestibular folds (false vocal cords). Lach is attached in front to the receding angle of the thyroid cartilage mmediately below the attachment of the thyro-epiglottic ligament, nd behind to the antero-lateral surface of the arytenoid cartilage little above the vocal process.

Vocal Ligaments (Inferior Thyro-arytenoid Ligaments).—These nportant ligaments, covered by mucous membrane, constitute the ocal folds (true vocal cords), and each is continuous with the upper •art of the expanded lateral portion of the crico-vocal membrane. Lach is composed of yellow elastic tissue, and with its fellow is attached 1 front to the receding angle of the thyroid cartilage at its centre nd behind to the vocal process of the arytenoid cartilage. Its inner order, which is covered by mucous membrane, is free and clearly efined. In its front part there is a very small nodule of elastic artilage.

Crico-thyroid Joint.—This belongs to the class of synovial joints.

'he articular surfaces are the facet on the inner surface of the inferior orn of the thyroid cartilage, and that on the outer surface of the ricoid cartilage posteriorly. The joint is surrounded by a capsular gament, and this is lined with a synovial membrane. The moveaents allowed are as follows: (1) rotation of the thyroid cartilage round n axis passing transversely through both joints; and (2) gliding, in diich the cricoid moves upwards and backwards, or downwards and Drwards, this movement partaking somewhat of a swinging character.

The recurrent laryngeal nerve ascends close behind the cricohyroid joint before entering the larynx.

Crico-arytenoid Joint.—This belongs to the class of synovial oints. The articular surfaces are the convex facet on the superior 'order of the cricoid cartilage posteriorly, and the concave under urface of the base of the arytenoid cartilage. The joint is surrounded y a capsular ligament, and this is lined with a synovial membrane, he movements allowed are as follows: (1) rotation, in which the rytenoid cartilage rotates on a nearly vertical axis, the effect being 0 invert or evert the vocal process; and (2) gliding in a lateral direction,

1 which one cartilage moves inwards towards its fellow, or outwards way from its fellow.


1386


A MANUAL OF ANATOMY


The corniculate cartilages are usually connected to the arytenoit cartilages by fibrous tissue, but in some cases there is a synovia articulation.

Prelaryngeal Lymph Glands.—One or two glands may lie upon tin median portion of the crico-vocal membrane in the interval betweei


Root of Tongue



Epiglottis


Ary-epiglottic Fold


Vestibular Fold Ventricle Vocal Fold Cuneiform Cartilage


Vocal Process of Arytenoid Cartilage


the crico-thyroid muscles. Thei afferent vessels are derived fron

(1) the infraglottic portion of th larynx, the lymphatics from whicl pierce the crico-vocal membrane

(2) the beginning of the trachea and (3) the upper part of the isthmu of the thyroid gland. Their efferen vessels pass either to the inferio deep cervical lymph glands, or t< the pretracheal glands as an inter mediate gland-station.

The Cavity of the Larynx.—Tb inlet of the larynx is situated be hind and below the epiglottis. I is triangular, being wide in fron and narrow behind, and its plan is sloped obliquely downwards an( backwards. Above and in front i n ls bounded by the epiglottis, am behind by the fold of mucous membrane which stretches between the arytenoid cartilages. On either side are the prominent ary-epiglottic folds, which extend from the tips of the arytenoid cartilages to the sides of the epiglottis and contain muscular fibres. Each of these folds, close to the arytenoid cartilage, contains the corniculate cartilage, which gives rise to a slight elevation, and a little in front of this another slight elevation is produced by the cuneiform cartilage. Between the arytenoid cartilage and the back part of the aryepiglottic fold medially and the back


Rima Glottidis Corniculate Cartilage

Fig. 842. — The Inlet of the Larynx and Adjacent Parts.


Epiglottis


Vestibule


Lamina of Thyroid Cartilage Middle Part


Cricoid Cartilage


Lower Part


Trachea


part of the lamina of the thyroid Fig. 843. —Vertical Transvers cartilage laterally there is a depression, Section of the Larynx, shov opening upwards, called the pyriform ing the Posterior Surface c

fossa. This is important, because unless Organ^Marshaix) ALF ° F ™ an instrument intended for the interior (Marshall).

of the larynx is kept carefully to the mid-line it will enter the foss and be pressed against its floor, just below the mucous membrane ( which the internal laryngeal nerve passes on its way to the larynx.













THE HEAD AND NECK


1387


The cavity of the larynx begins at the inlet, and ends on a level with he lower border of the cricoid cartilage. It is divided into three ompartments by means of two antero-posterior folds of mucous nembrane, which project into it from each lateral wall. The upper >air of folds are called the vestibular cords, and the lower pair the r ocal folds. The upper compartment is known as the vestibule of he larynx, and it extends as low as the vestibular folds. It is wider bove than below, and its anterior depth exceeds the posterior. The niddle part is situated between the vestibular folds above and the meal folds below. On either side is a recess, called the sinus of the arynx (ventricle). This is bounded above by a vestibular fold, and >elow by a vocal fold. Its outer wall is covered by fibres of the hyro-arytenoid muscle. At the anterior part of the sinus there is


Fig. 844. —Sagittal Section of the Larynx and Trachea, showing the Vocal Folds and Sinus of the Right Side.


1 small valvular aperture, which leads to a diverticulum of the ventricle, called the saccule of the larynx. This extends upwards Detween the vestibular fold and the lamina of the thyroid cartilage, reaching as high as the upper border of the latter. On its medial aspect there are some muscular fibres, which are known as the compressor sacculi laryngis.

The lower part of the larynx is compressed from side to side above, but becomes circular inferiorly, where it opens into the trachea.

The vestibular folds (false vocal cords) are two folds of mucous membrane, which extend at either side from the receding angle of the thyroid cartilage immediately below the attachment of the thyroepiglottic ligament to the antero-lateral surface of the arytenoid cartilage a little above the vocal process. Each contains some fibrous









1388


A MANUAL OF ANATOMY


tissue, forming the vestibular ligament. The vestibular folds ar widely separated from each other by an interval known as the rim vestibuli [false glottis), so that the vocal folds are visible on lookin into the larynx from above.

The vocal folds (true vocal cords) are concerned in the productioi of the voice. They are prominent folds at either side, which ar rather less than an inch in length, and extend from the receding angl of the thyroid cartilage to the vocal process of each arytenoid cartilage Each cord consists of the vocal ligament, which is continuous with th upper part of the expanded lateral portion of the crico-vocal membrane

and is composed of yellow elastic


Thyroid Notch


Lamina of Thyroid Cartilage / JMljift fif

/J


Thyro-arytenoideus


Vocal Fold '


Crico-arytenoideus

Lateralis


Arytenoid Cartilage

Crico-arytenoideus Posterior


Arytenoideus


tissue. The mucous membran< covering the fold is thin, anc firmly adherent to the elastii tissue of the ligament, and it has ; characteristic pearly white colour The vocal folds are much nearei to each other than the false, s( that the latter are not visible when the larynx is viewed froir below.

Rima Glottidis.—The rima glottidis, or true glottis, is the narrov fissure by which the upper anc lower parts of the larynx communicate with each other, and il


Tig. 845. Dissection of the Larynx, fUp narrowest nart of f-fie ravhv showing the Muscles, Vocal Folds 1 + • narro ^ e ^ P art °* tne cavl y and Rima Glottidis (Superior 1S elongated from before backView) . wards, and is narrow in front at

. the receding angle of the thyroid

cartilage, but wider behind, where it is closed by the interarytenoid ° d °1 mucous membrane. It is divisible into an intermembranous, part and an inter cartilaginous part. The intermembranous part is nari ow, and is bounded on either side by the vocal cord. Its length is rather less than an inch, and it forms about two-thirds of the entire aperture. The intercartilaginous part is wider than the intermembranous part, and is bounded on either side by the inner aspect oi the base of the arytenoid cartilage. It is about J inch in length, an ^orms about one-third of the length of the entire aperture.

The shape of the rima glottidis is subject to alteration, and has to be considered under three conditions:

( I ) During quiet respiration it has the form of an elongated triangle, the apex being in front at the thyroid cartilage, and the base behind at the mterarytenoid fold of mucous membrane. (2) During a deep inspiration the rima is widely dilated, and assumes a diamond shape, the widest part being opposite the tips of the vocal processes of the aiytenoid cartilages, where the lateral angles of the diamond are placed, the posterior angle at the interarytenoid fold of mucous mem







THE HEAD AND NECK


1389


irane being truncated. (3) While talking, and especially in singing igh notes , the vocal folds become so closely approximated as to be ►ractically parallel, and the rima glottidis assumes the form of a narrow

hink.

Mucous Membrane of the Larynx.—This is continuous above with he mucous membrane of the pharynx, and below with that of the rachea. Above the level of the rima glottidis its subjacent attachment is loose on account of the presence of submucous areolar tissue, articularly near the ary-epiglottic folds, a condition which favours


Epiglottis and its Tubercle


Sinus of Larynx,


Vestibular Fold


Vocal Fold Cuneiform Cartilage Corniculate Cartilage ■""* __ Tip of Arytenoid Cartilage





r iG. 846. —The Inlet of the Larynx and the Rima Glottidis, as seen by the Aid of the Laryngoscope under Different Conditions.

(The Figures on the left side are copied from Czermak.)

A, Ordinary quiet inspiration C, Vocalization, especially in singing high notes

B, Very deep inspiration R.G. Rima glottidis


he occurrence of oedema, but over the laryngeal surface of the epiglottis it is firmly attached. Over the vocal folds it is very thin, md is so firmly connected to the vocal ligaments that oedema cannot >ass this point. The membrane is covered by ciliated columnar pithelium, except (1) near the margin of the ary-epiglottic folds, vhere it is of the stratified squamous variety, as in the laryngeal )ortion of the pharynx and the cavity of the mouth; and (2) over the X)cal folds, where it is also of the stratified squamous vaiiety. Bodies esembling the taste-buds of the tongue are met with on the laryngeal surface of the epiglottis, the inner surfaces of the arytenoid cartilages








1390


A MANUAL OF ANATOMY


and of the ary-epiglottic folds, and over the margins of the vestibula folds.

The mucous membrane contains a large number of acinous mucou glands, the ducts of which open freely on the surface, except over th vocal folds, where there are no glands. They are arranged in the follow ing groups: (i) epiglottic glands, which are very numerous, and occup; the pits on the laryngeal surface of the epiglottis; (2) arytenoid glands in front of the arytenoid cartilages, and in the adjacent portions 0 the ary-epiglottic folds; (3) along the vestibular folds; and (4) in th wall of the laryngeal saccule, where they are very numerous.

It is of practical importance to remember that an opening mad in the crico-thyroid space enters the larynx below the vocal folds


Epiglottis

Superior Horn of Thyroid Cartilage

Cuneiform Cartilage Corniculate Cartilage

Arytenoideus Obliquus Arytenoideus Transversus

Crico-arytenoideus Posterior Crico-thyroid Joint


Cricoid


Fig. 847. —The Intrinsic Muscles of the Larynx (Posterior View).

consequently, in those cases in which suffocation is threatened b} a foreign body impacted in the upper part of the larynx, the simpb operation of laryngotomy or incising the crico-thyroid space wil usually give relief.

Intrinsic Muscles. —-These are the muscles by which the cartilages are moved and the condition of the vocal folds determined. They art the crico-thyroideus, crico-arytenoideus posterior, crico-arytenoideus lateralis, thyro-arytenoideus, arytenoideus, and aryepiglotticus. The arytenoideus is a single muscle, but all the others are arranged ir pairs.

Crico-thyroideus — Origin .—The antero-lateral part of the cricoic cartilage.







THE HEAD AND NECK


I 39 i


Insertion .—The lower margin of the lamina of the thyroid cartilage, id the front of the inferior horn.

Nerve-supply .—The external laryngeal branch of the superior ryngeal nerve.

The fibres are directed upwards and backwards in a diverging Lanner, the posterior being horizontal and the anterior oblique, hese two sets of fibres are often distinct.

Action .—To approximate the front parts of the cricoid and thyroid irtilages in the following manner: the posterior horizontal fibres raw the cricoid cartilage backwards, and the anterior oblique fibres


Fig. 848.—The Intrinsic Muscles of the Larynx (Lateral View).

The greater part of the right lamina of the thyroid cartilage has

been removed.


levate the anterior part of the cricoid cartilage. As a result of this aovement the posterior part of the cricoid cartilage, carrying the .rytenoid cartilages on its upper border, is depressed and carried >ackward. Thus the vocal folds are put upon the stretch, and the uuscle is a tensor of the fold.

Between the two muscles anteriorly there is a triangular interval ibout ^ inch wide, in which the central portion of the crico-vocal nembrane is visible, this portion being crossed at its centre by the

rico-thyroid arch of arteries. In this region, just above the cricoid
artilage, laryngotomy may be performed.





















1392


A MANUAL OF ANATOMY


Crico-arytenoideus Posterior (see Fig. 847)— Origin. —The posterior

surface of the cricoid cartilage on one side of the median vertical ridge.

Insertion. —The posterior aspect of the muscular process of the arytenoid cartilage.

Nerve-supply. —The recurrent laryngeal nerve.

The fibres of the muscle are directed upwards and outwards, the highest being short and nearly horizontal, the middle being oblique, and the lowest almost vertical.

Action. —To draw the muscular process of the arytenoid cartilage backwards, thereby swinging the vocal process outwards, the result of which is to open the rima glottidis. The muscle is, therefore, a dilator of the rima glottidis.

The muscle is separated from its fellow by the median vertical ridge on the back of the cricoid cartilage.

Crico-arytenoideus Lateralis (see Fig. 848)— Origin— The lateral portion of the cricoid cartilage along its upper sloping border, extending as far back as the crico-arytenoid joint.

Insertion. —The anterior aspect of the muscular process of the arytenoid cartilage, and the adjacent portion of the antero-lateral surface.

Nerve-supply. —The recurrent laryngeal nerve.

The fibres of the muscle are directed backwards and upwards.

Action. —To draw the muscular process of the arytenoid cartilage forwards, thereby swinging the vocal process inwards, the result of which is to narrow the rima glottidis. The two muscles therefore approximate the vocal folds, and come into action in speaking. When the crico-arytenoidei posteriores et laterales act together they prevent rotation, and thus indirectly assist the arytenoideus in approximating the arytenoid cartilages, and so the rima glottidis is closed. The crico-arytenoideus lateralis is covered laterally by the lamina of the thyroid cartilage and the upper fibres of the crico-thyroideus, and medially by the lateral expanded portion of the crico-vocal membrane.

Thyro-arytenoideus.— This muscle consists of two parts, lateral and medial.

Lateral Part— Origin. —(1) The lower half of the inner surface of the lamina of the thyroid cartilage, and (2) the outer surface of the lateral portion of the crico-vocal membrane.

Insertion. —The front of the muscular process and the adjacent part of the outer border of the arytenoid cartilage, a few of the fibres passing round the cartilage to become continuous with the arytenoideus. The uppermost fibres of this part pass upwards and backwards to the ary-epiglottic fold, and thence to the epiglottis, under the name of the thyro-epiglotticus.

Medial Portion — Origin. — (1) The receding angle of the thyroid cartilage, and (2) the anterior part of the vocal fold. The most medial fibres of this portion, known as the vocalis muscle, spring from the anterior part of the vocal fold.


THE HEAD AND NECK


1393


Insertion .—The outer surface of the vocal process of the arytenoid rtilage, and the neighbouring part of the antero-lateral surface.

The fibres pass from before backwards, some of them having a

  • ht inclination outwards, and the highest backwards.

Nerve-supply .—The recurrent laryngeal nerve.

Action —(1) Medial Part.—To draw forwards the arytenoid cartilage, d the posterior part of the cricoid cartilage, swinging the latter in upward and forward direction, e result of this action is to relax 3 vocal folds by approximating the ctenoid cartilage to the thyroid carti(e. This part of the muscle is, srefore, the antagonist of the cricoyroideus. It is to be borne in mind, wever, that one factor in relaxation the vocal folds must of necessity be istic recoil. The fibres representing 3 vocalis muscle act by rendering lse that part of the vocal, fold which in front of them, and relaxing the rt behind them.

A very important action of the idial part of the thyro-arytenoideus, len it is acting in conjunction with 3 crico-thyroid, is accurately to approximate and straighten the cal fold. A loss of accurate fitting of the fold of one side against

fellow is one of the first signs of incipient paralysis of the recurrent •yngeal nerve from pressure or stretching, and, when it happens on e left side, suggests an intrathoracic aneurism or new growth. The tion of the vocalis part of the thyro-arytenoideus is to tighten a rtion of the vocal fold, and may be concerned in the production of e falsetto voice.

(2) Lateral Part.—In virtue of its insertion into the muscular process the arytenoid cartilage, this portion will draw forwards that process, e effect of which is to swing inwards the vocal process. The fibres own as the thyro-epiglotticus have been supposed to assist in pressing the epiglottis.

The outer portion of the muscle lies within the lamina of the thyroid rtilage. Its lower border touches the crico-arytenoideus lateralis, d its upper fibres lie on the outer wall of the sinus and saccule. The tier portion of the muscle is in close contact with the outer side of e vocal fold.

Arytenoideus.—The arytenoideus muscle lies across the posterior rfaces of the arytenoid cartilages. It consists of two parts—superial and deep. The superficial part is composed of two decussating ndles, each of which is known as the arytenoideus obliquus; and e deep part constitutes the arytenoideus transversus.

Arytenoideus Obliquus.—Each of these muscles, which has the

88


Fig. 849. — Scheme to show Actions on the Arytenoid Cartilage of Lateral and Posterior Crico-arytenoids (CAL, CAP) and Thyro-aryTENOID (TA).





1394


A MANUAL OF ANATOMY


form of a narrow oblique bundle, arises from the back of the muscu process of the arytenoid cartilage. Its direction is upwards a inwards, and at the median line it decussates with its fellow of 1 opposite side, thus X. Having reached the summit of the oppos arytenoid cartilage, a few of the fibres end, but the majority en

the corresponding a:


Fig. 850. —Skeletal Structures of Larynx, with Crico-thyroid Muscle in Position.


epiglottic fold. Being inforced by a few fib from the summit of 1 arytenoid cartilage, i fibres now constitute i ary - epiglotticus muse which passes forwai within the ary-epiglot fold to be inserted ir the side of the epiglotl Associated with the ai epiglotticus there are th< fibres of the lateral porti of the thyro-arytenoide which are known as 1 thyro-epiglotticus.

Nerve-supply .—The current laryngeal nerve.

Action .—The two mi cles, having the arytem


cartilages within their embrace, draw these cartilages together, which action they are aided by the arytenoideus transversus a ary-epiglotticus muscles, and the inlet of the larynx is narrowed.

Arytenoideus Transversus.—The fibres of this muscle extend trai versely from the posterior surface and outer border of one arytenc cartilage to those of the other.

Nerve-supply .—The recurrent laryngeal nerve.

Action .—To draw the arytenoid cartilages together, and th approximate the vocal folds, and even close the rima glottidis.

The arytenoideus transversus muscle, clothed with mucous me: brane anteriorly, bounds the rima glottidis posteriorly; and its sup ficial or posterior surface is in contact with the decussating arytenok obliqui muscles.

Compressor Sacculi Laryngis is a thin layer of muscular fibres the medial side and upper end of the saccule of the larynx. The fibi are related superiorly to those of the ary-epiglotticus, which are cc tained within the ary-epiglottic fold.

Summary of the Actions of the Laryngeal Muscles.—The intrin muscles of the larynx, by regulating the condition of the rima glottid contribute to vocalization, and modify the pitch of notes. In so doi they lengthen, so as to render tense, or shorten, so as to relax, t vocal folds; and they also bring the folds together, or draw th(







THE HEAD AND NECK


1395


art. In other words, the intrinsic muscles bring about tension and vallelism of the true vocal folds, or give rise to the opposite conions—namely, relaxation and divergence.

Tension is effected by the crico-thyroidei muscles (see p. 1390). Convergence of the vocal folds is effected by the crico-arytenoidei erales and the arytenoidei.

Relaxation of the vocal folds is brought about by the thyro-aryloidei muscles, which draw the arytenoid cartilages, along with the sterior part of the cricoid cartilage, forwards. The vocal folds are the same time shortened by their own elastic recoil. The fibres of 3 thyro-arytenoideus muscle, known as the vocalis, act by producing

al variations in tension.

Divergence of the vocal folds and opening of the rima glottidis is

ected by the crico-arytenoidei posteriores, which draw the muscular Dcesses of the arytenoid cartilages backwards and inwards, the result which is to rotate the vocal processes outwards.

Function of the Epiglottis.—The epiglottis is never folded down like id. The superior aperture of the larynx is closed during deglutition the action of the arytenoideus transversus and the lateral portions the thyro-arytenoidei. The arytenoideus transversus approximates e arytenoid cartilages, and the lateral portions of the thyro^tenoidei draw the arytenoid cartilages forwards until their apical rts come into contact with the tubercle of the epiglottis.

The sphincter-like action of the ary-epiglottici upon the inlet of the •ynx must also be taken into account.

Nerves.—The nerves of the larynx are the superior and recurrent ■yngeal, both of which are branches of the vagus.

The superior laryngeal nerve divides into two branches, external d internal. The external laryngeal nerve, which is comparatively lall, supplies the crico-thyroideus, and also gives twigs to the inferior nstrictor muscle of the pharynx. The internal laryngeal nerve is isory, passes deep to the posterior border of the thyro-hyoid muscle, d enters the larynx by piercing the thyro-hyoid membrane in comny with the superior laryngeal artery, above which it lies. Crossing e floor of the pyriform fossa, where a ganglion is situated upon it, breaks up into branches, some of which ascend to the ary-epiglottic Id and epiglottis, a few of them passing as far as the posterior suiface the tongue close to the mid-line. The other branches descend supply the laryngeal mucous membrane, and one of them joins a

dg from the recurrent laryngeal nerve.

The recurrent laryngeal nerve is the principal motor nerve 01 the rynx. On the right side it arises from the vagus at the root of the ck, and hooks round the first part of the right subclavian artery. 1 the left side it arises from the vagus in the upper part of the thorax,

id hooks round the arch of the aorta.

Having ascended in the groove between the trachea and oesophagus, at the side of the trachea, it passes beneath the lower border ot the ferior constrictor muscle, and ascends upon the cricoid carti age,


1396


A MANUAL OF ANATOMY


lying close behind the crico-thyroid joint. Here it divides into t\ branches, anterior and posterior. The anterior branch ascends und cover of the thyroid cartilage, and is distributed to the crico-ar tenoideus lateralis, thyro-arytenoideus, thyro-epiglotticus, and ar epiglotticus muscles. The posterior branch passes upwards on t' back of the cricoid cartilage beneath the crico-arytenoideus posteri muscle, which it supplies, and then it goes on to end in the arytenoide muscle.

Perhaps the most practically important relation of the recurre laryngeal is the thyroid gland, since it passes just behind the pla where that structure is most firmly attached to the cricoid cartila ; and first ring of the trachea. During removal of one half of tl thyroid the nerve is in great danger of being cut in freeing the glan particularly as it is so often farther forward than its reputed positi< in the groove between the trachea and oesophagus. Its relation the inferior thyroid artery is variable, and branches often pass bo in front of and behind the nerve, though most commonly the arte: is in front. It has been noticed already that, in its course, the ner is in close relation with the paratracheal lymph glands.

The recurrent laryngeal nerve carries some sensory branches the mucous membrane of the larynx below the rima glottidis, and communicates with the internal branch of the superior larynge; The motor fibres of the external branch of the superior laryngeal ai of the inferior laryngeal are derived from the cranial root of the acce sory nerve.

Summary of the Laryngeal Nerves. —The superior laryngeal nerve, throui its internal branch, is sensory, and its external branch supplies the crico-thyroide and in part the inferior constrictor muscle of the pharynx.

The inferior or recurrent laryngeal nerve is chiefly motor, and it suppli

the intrinsic muscles of the larynx, with the single exception of the crico-thyroidev it also supplies a twig to the inferior constrictor.

Arteries. —The arteries of the larynx are the superior and tl inferior laryngeal. The superior laryngeal artery is a branch of tl superior thyroid. It accompanies the internal laryngeal nerve, belc which it lies, and enters the larynx by piercing the thyro-hyoid mer brane. The inferior laryngeal artery is a branch of the inferior thyroi and it accompanies the recurrent laryngeal nerve.

Veins. —The superior laryngeal vein opens into the superior thyroi and the inferior laryngeal vein into the inferior thyroid vein.

Lymphatics. —These are arranged in two sets—superior and inferic ihe superior lymphatics come from the portion of the larynx abo 1 the rima glottidis. Having pierced the thyro-hyoid membrane, th< pass to the upper group of deep cervical lymph glands. The inferi lymphatics come from the portion of the larynx below the rin glottidis. Having pierced the crico-vocal membrane, they pass the lower group of deep cervical lymph glands, having previous traversed the pre- and para-laryngeal lymph glands.

In early life the larynx occupies a higher position than it does


THE HEAD AND NECK


1397


adult, its descent, which is gradual, being completed by puberty, to that period the projection known as the laryngeal prominence lot present. After puberty important changes take place. The tilages increase in size, the laryngeal prominence assumes marked r elopment, especially in the male, and the vocal folds undergo rease in length. These various changes account for the modifications ich the voice undergoes at and after puberty.

Development of the Larynx. —The larynx is developed from the upper part 1 median diverticulum from the ventral aspect of the fore-gut, which diverilum by its lower part gives rise to the trachea. The general development is sn on p. 73. The epiglottis is formed from the caudal part of the hypochial eminence, its pharyngo-epiglottic fold being a remnant of the third h and its ary-epiglottic fold of the fourth arch. The cricoid is formed in sixth arch, as are the internal intrinsic muscles. The thyroid cartilage r elops in the ventral part of the fourth arch, the lower part of the inferior strictor belonging to the dorsal part; the crico-thyroideus is a part of this scle cut off by the downgrowth of the lower thyroid horn to meet the cricoid. 3 vocal folds are formed in the edges of the original sagittal opening in the iryngeal floor; the part of the larynx above the folds is a modification of 3 floor, while the lower part comes from the upper end of the pulmonary growth. The pyriform fossa marks the site of the third lateral pouch.


Prevertebral Muscles.

Longus Capitis (Rectus Capitis Anticus Major) — Origin .—By four art tendons from the anterior tubercles of the transverse processes the third, fourth, fifth, and sixth cervical vertebrae, the same tachment as that of the scalenus anterior.

Insertion .—The inferior surface of the basilar process of the occipital ne, from the pharyngeal tubercle obliquely outwards and forwards r about \ inch.

Nerve-supply. —The cervical plexus.

The muscle is directed upwards and inwards.

Action. —To flex the head and neck.

Relations — Anterior. —The upper part of the common carotid and e internal carotid arteries, the internal jugular vein, the vagus

rve and sympathetic trunk, and the pharynx. Posterior . A part

the longus cervicis, a large portion of the rectus capitis anterior, id the transverse processes of the cervical vertebrae.

Rectus Capitis Anterior (Rectus Capitis Anticus Minor)— Origin.— le front of the lateral mass of the atlas.

Insertion.— The inferior surface of the basilar part of the occipital >ne between the foramen magnum and the outer part of the insertion

the longus capitis. .

Nerve-supply. —The anterior primary ramus of the first cervical

irve.

The muscle is directed upwards and slightly inwards.

A ction. —To flex the head.

Rectus Capitis Lateralis— Origin.— The upper aspect of the exemity of the transverse process of the atlas at its front part.


1398 A MANUAL OF ANATOMY

Insertion. —The inferior surface of the jugular process of tl occipital bone.

Nerve-supply. —The anterior primary ramus of the first cervic nerve.

Relations. — Anteriorly is the internal jugular vein, with the vagi accessory, and hypoglossal nerves close to it, while only a little distam in front is the styloid process, parotid gland, and facial nerve. Po teriorly is the obliquus capitis superior. Laterally are the occipit


Basilar Part of Occiptal Bone


Rectus Capitis Anterior,


Rectus Capitis Lateralis —


Longus Capitis


Scalenus Posterior


Vertebral Artery (third part)


-Longus Cervicis (upper oblique part) Vertebral Artery (second part)


Scalenus Anterior


Scalenus Medius


Longus Cervicis (vertical part)


---Vertebral Artery (first part)

-Longus Cervicis (lower oblique

'• part)


Scalene Tubercle


Fig. 851. —The Right Prevertebral Muscles. The vertebral artery is also shown.


artery, and often the accessory nerve, forming an X, and still mo superficially the origin of the digastric; while medially the vertebr artery comes up through the foramen transversarium.

The muscle passes vertically upwards.

Action. —To incline the head to one side.

Longus Cervicis (Longus Colli). —This muscle consists of thr< portions—superior oblique, vertical, and inferior oblique.

Superior Oblique Portion— Origin. —The anterior tubercles of tt












THE HEAD AND NECK


1399


lsverse processes of the third, fourth, fifth, and sixth cervical tebrse.

Insertion. —The lateral aspect of the tubercle on the anterior arch. The fibres are directed upwards and inwards.

Vertical Portion— Origin. —The fronts of the bodies of the last two /ical and first three thoracic vertebrae.

Insertion. —The fronts of the bodies of the second, third, and fourth /ical vertebrae.

Inferior Oblique Portion — Origin. —The fronts of the bodies of the t three thoracic vertebrae in common with the lower portion of the tical part.

Insertion. —The anterior tubercles of the transverse processes of fifth and sixth cervical vertebrae.

Nerve-supply .—The anterior primary rami of the adjacent spinal ves.

Action. —To flex the cervical part of the vertebral column.

Relations — Anterior. —The pharynx, oesophagus, and retro-pharyn.1 cellular tissue; the common and internal carotid arteries, and ernal jugular vein; the vagus nerve, and the sympathetic trunk;

longus capitis superiorly; and the recurrent laryngeal nerve, inferior

rroid artery, and first part of the subclavian artery infenorly. sterior.— The bodies and discs of the adjacent vertebrae, and their ns verse processes.

Petrous Portion of the Internal Carotid Artery.— This part of the ernal carotid artery is contained within the carotid canal of the trous part of the temporal bone. It is at first directed upwards, i then, describing a bend, it passes forwards and inwards to the amen lacerum, where it enters upon the cavernous part of its course, e vessel is surrounded by a plexus of veins, and is accompanied by 3 internal carotid branch of the superior cervical ganglion of the [apathetic trunk. This branch breaks up into two divisions. One these lies on the outer side of the artery and gives rise to the m'nal carotid sympathetic plexus, whilst the other lies on the inner Le of the artery and goes on to form the medial part of the latter

iXUS

As the artery ascends in the carotid canal it is situated in front , and below, the tympanic cavity and cochlea; as it bends it has the Laryngo-tympanic tube on its anterior and outer side, and as it ,sses forwards and inwards it has the trigeminal ganglion above it, e partition between the two being partly membranous.

Branches.— The petrous portion gives off a carotico-tympamc branch 1, hich enters the tympanic cavity through the posterior wall of the .rotid canal, and it may furnish a petrosal branch to accompany t e

iep petrosal nerve. .. ,

For the cavernous portion of the internal carotid artery, see p. 1109.

Petrous Part of the Facial Nerve.— This part of the nerve extend, om the orifice of the internal auditory meatus, on the posterior irface of the petrous part of the temporal bone, to the stylo-mastoid


1400


A MANUAL OF ANATOMY


foramen, and it traverses (1) the internal auditory meatus, and (2) t] facial canal.

Meatal Portion. —The motor root of the nerve is directed outwarc and is accompanied by the sensory root (pars intermedia of Wrisber^ the auditory nerve, and the internal auditory artery. It is plac< upon the upper and anterior aspect of the auditory nerve, and t] sensory root lies between the two, and here joins the facial nerv At the deep end of the internal auditory meatus the facial ner parts company with the auditory nerve, and enters the faci canal.

Branches. — Two branches connect the facial nerve with the auditoi nerve.

Tympanic Plexus


Iog. 852. Relations of the Petrous Portion of the Internal

Carotid Artery.


Portion in the Facial Canal (Aqueduct of Fallopius). —The directic of this portion of the nerve corresponds to that of the canal. It divided into three stages. In the first stage, which is very short, tl nerve passes horizontally outwards, between the cochlea and vestibul to the inner wall of the tympanic cavity, where there is an enlargemen called the facial ganglion (geniculate ganglion). Here it bends sharph and in the second stage passes backwards, lying above the fenesti vestibuli and enclosed in a very thin-walled bony canal which ma easily be damaged in scraping the inner wall of the tympanic cavit 1 Then it describes another less abrupt curve, and in the third sta{ descends behind the posterior wall of the tympanic cavity to the styl< mastoid foramen, by which it escapes from the facial canal. Tl hiatus for greater superficial petrosal nerve {hiatus Fallopii) leads froi near the beginning of the facial canal to the superior surface of tl





THE HEAD AND NECK


1401


etrous part of the temporal bone. As the facial canal descends it ommunicates with the canal of the pyramidal eminence of the tympanic avity, and below this is another opening, called the posterior canaliulus for the chorda tympani nerve.


Fig. 853.

heater superficial petrosal nerve is seen lying on bone, exposed by removal of dura mater. It enters foramen lacerum, having passed deep to trigeminal ganglion. In the foramen lies by lateral side of internal carotid and its plexus; is joined by a branch from this, and enters interpterygoid foramen.


Branches :

Emm (Greater superficial petrosal (to spheno-palatine ganglion).

facial I Communicating branch to lesser superficial petrosal (to the otic

ganglion | Externa^petrosal (to sympathetic plexus on middle meningeal artery).*

Nerve to the stapedius muscle.

Chorda tympani nerve.

Communicating branch to the auricular branch of the vagus.

The greater superficial petrosal nerve arises from the facial ganglion, ind passes forwards through the corresponding hiatus, by which it eaves the facial canal. It then courses inwards and forwards in a (roove on the anterior surface of the petrous part of the temporal

  • There is grave doubt whether this nerve really exists in the body.





1402


A MANUAL OF ANATOMY


bone, and passes beneath the trigeminal ganglion to the foramei lacerum. In the upper part of this foramen it joins the deep petrosa nerve from the internal carotid plexus to form the nerve of the pterygoi( canal, which passes forwards through the pterygoid canal into th pterygo-palatine fossa, and joins the back part of the spheno-palatim ganglion. The greater superficial petrosal nerve contains some moto fibres, but to a large extent it consists of sensory fibres. These repre sent peripheral branches of the unipolar cells of the facial ganglion the central branches of which give rise to the sensory root of the facia nerve.

A communicating branch passes from the facial ganglion to th lesser superficial petrosal nerve, which latter represents the tympani* branch of the glosso-pharyngeal after it has left the tympanic plexu; on the promontory of the inner wall of the tympanic cavity. IT means of the lesser superficial petrosal nerve this communicating branch reaches the otic ganglion.

The external petrosal nerve is said to pass through an opening just within the orifice of the hiatus for greater superficial nerve, an( to join the sympathetic plexus around the middle meningeal artery.

The nerve to the stapedius muscle arises from the facial nerve ii the descending part of the facial canal opposite the pyramidal eminence of the tympanic cavity. It enters a small canal in the pyramida eminence, and so reaches the stapedius as that muscle lies within th canal.

The chorda tympani nerve arises in the facial ganglion, but is bounc up with the facial nerve in the descending part of the facial canal A little above the stylo-mastoid foramen it leaves the nerve, anc passes upwards and forwards in a recurrent course through a minut< canal, called the posterior canaliculus for chorda tympani nerve, b] which it enters the tympanic cavity. At first it is placed on th posterior wall of the tympanic cavity close to the posterior margii of the tympanic cavity, and to the outer side of the pyramidal eminence The nerve then passes forwards medial to the tympanic membram near its upper margin, lying between its mucous and fibrous layers, s< as to be ensheathed by the mucous membrane. In this part of it: course it passes between the inner aspect of the handle of the malleu and the limb of the incus. Having arrived at the inner end of th petro-tympanic fissure, it leaves the tympanic membrane by passing through the anterior canaliculus for chorda tympani nerve (canal 0 Huguier). It grooves the spine of the sphenoid, and then enters th pterygo-maxillary region, and passes downwards and forwards deep t< the lateral pterygoid muscle, where it receives a communicating twi{ from the otic ganglion, and then joins the lingual nerve at an acut* angle at the upper margin of the medial pterygoid muscle. It shoul( be noted that the chorda tympani lies deep to all the vessels and nerve with which it comes in contact in the pterygoid region. The distribu tion of the nerve has been already described (see p. 1315) The chorda tympani is composed of fibres, which are the peri


THE HEAD AND NECK


I 4°3


iheral processes of the unipolar cells of the ganglion of the facial erve. These represent the fibres which are distributed to the sides nd dorsum of the tongue over its anterior two-thirds. They are herefore regarded as gustatory, and functionally are afferent. They re connected with the fibres of the sensory root by means of the mipolar cells of the ganglion of the facial nerve. The chorda tympani terve, however, also contains secretory fibres of the submandibular nd sublingual glands. The nerve is therefore a mixed nerve.

A communicating branch is given off from the facial nerve just hove the stylo-mastoid foramen, which connects it with the auricular •ranch of the vagus.

Sensory Root of Facial Nerve (Pars Intermedia of Wrisberg).—

"he fibres of this small nerve arise from the unipolar cells of the ganglion if the facial, being the central processes of these cells, the peripheral >rocesses representing the principal fibres of origin of the chorda ympani. The sensory root is at first closely incorporated with motor oot of the facial nerve, and passes from the facial canal into the nternal auditory meatus. Here it separates from the facial nerve, nd lies between it and the auditory nerve. After passing through the irifice of the internal auditory meatus the sensory runs to the lower )order of the pons, where it enters the medulla oblongata, and ends n the nucleus of the tractus solitarius.

The Ganglion of the Facial Nerve (Geniculate Ganglion). —The acial ganglion is situated on the facial nerve in the facial canal it the point where the canal, having reached the inner wall of the ympanic cavity, makes a sharp bend before passing backwards, fike a spinal ganglion and the trigeminal ganglion, it consists of unipolar

ells, each of which has a central and a peripheral process. The

ganglion is the nucleus of origin of the sensory fibres of the facial lerve. The central processes of the unipolar cells form the sensory 'oot of the facial nerve, and the majority of the peripheral processes orm the chorda tympani nerve. Some of the peripheral processes, lowever, pass into the greater superficial petrosal nerve and the

ommunicating branch to the lesser superficial petrosal nerve.

Summary of the Petrosal Nerves. —There are four petrosal nerves—namely, greater superficial, lesser superficial, external, and deep; and there are two deep )etrosal nerves—namely, great and small.

Superficial Petrosal Nerves. —The greater superficial petrosal nerve is described

>n p. 1401.

The lesser superficial petrosal nerve issues from the tympanic plexus on the nner wall of the tympanic cavity, and represents the continuation of the tympanic )ranch of the inferior ganglion of the glosso-pharyngeal nerve. As it traverses 1 canal in the petrous portion of the temporal bone it is joined by a small branch rom the ganglion of the facial nerve. Emerging from this canal through the liatus for the lesser superficial petrosal nerve, it passes through the canaliculus nnominatus, when present, or through the fissure between the petrous portion >f the temporal bone and greater wing of the sphenoid, or sometimes through he foramen ovale, into the infratemporal fossa, where it joins the otic ganglion

lose below the foramen ovale.

The external petrosal nerve (of doubtful existence) is a branch of the ganglion >f the facial nerve. It leaves the petrous part of the temporal bone through


I 4°4


A MANUAL OF ANATOMY


a small opening (inconstant) close to the hiatus for greater superficial petrosa nerve, and joins the sympathetic plexus on the middle meningeal artery.

Deep Petrosal Nerve. —The deep petrosal nerve is a branch of the interna carotid plexus of the sympathetic. It joins the greater superficial petrosa in the upper part of the foramen lacerum medium to form the nerve of th pterygoid canal, which, as stated, passes through the latter canal into the pterygo palatine fossa, and joins the back part of the spheno-palatine ganglion.

The carotico-tympanic nerves from the tympanic plexus are often referrec to as the small deep petrosal nerves, which form a communication with the in ternal carotid plexus by piercing the wall of the carotid canal. There may b< more than one such connection between the two plexuses.

Auditory Nerve in the Internal Auditory Meatus. —This nerve passe outwards in the internal auditory meatus in company with the senson and motor roots of the facial nerve, and the internal auditory artery The motor root of the facial nerve is placed upon its upper and anterior aspect, and the sensory root lies between the two. Two branche: connect the auditory nerve with the facial.

At the deep end of the meatus the auditory nerve breaks up intc two divisions—an upper, called the vestibular, and a lower, called th( cochlear nerve. The vestibular ^nerve has a ganglion, called th(


Fig. 854.—Scheme of the Auditory Nerve (Flower).

C.F. Communicating with Facial E.S.C. To Lateral Semicircular Duct

C. Cochlear Nerve U. To Utricle

V. Vestibular Nerve S. To Saccule

S.S.C. To Superior Semicircular Duct P.S.C. To Posterior Semicircular Duct

vestibular ganglion [Scarpa s ganglion ), situated at the deep end of the meatus, its bipolar cells giving origin to the vestibular fibres. Latei it breaks up into two branches, upper and lower. The superior brand gives branches to the ampullary crests of the superior and latera. semicircular ducts, and to the utricle. These pass through the foramina of the superior vestibular area of the upper fossa of the lamina cribrosa at the deep end of the meatus (see Fig. 126, p. 190). The inferior branch supplies branches to the ampullary crest of the posterioi semicircular duct and to the saccule. The former pass through the foramen smgulare in the lower fossa of the lamina cribrosa, and the latter through the foramina of the inferior vestibular area of the lowei fossa of the lamina cribrosa.

The branches of the cochlear nerve pass through the foramina oi the cochlear area of the lower fossa of the lamina cribrosa.

The Joints of the Atlas, Axis, and Occipital Bone.

Atlanto-axial Joints. —These are three in number, and they belong to the class of synovial joints. One is medially placed, the articular surfaces being the atlantal facet on the anterior surface of the odontoid




THE HEAD AND NECK


1405


cess of the axis and the odontoid facet on the posterior surface the anterior arch of the atlas. This joint belongs to the subision of pivot-joints. The other two are placed one on either 3, the articular surfaces of each being the inferior articular process the atlas and the corresponding superior articular process of the s. These two joints belong to the subdivision of plane-joints. Ligaments. —These are the transverse ligament, the capsular iments, and the accessory ligaments. Besides these there are the Dermost part of the anterior longitudinal ligament and the posterior mto-axial ligament, which are not directly related to any of the ats.

The transverse ligament of the atlas is the transverse portion of the ciate ligament, to be presently referred to, and is a strong band, ich is attached on either side to the tubercle on the inner aspect


Tubercle on Ant erior_ Arch of Atlas


Spine of Axis

Fig. 855._The Articulation between the Anterior Arch of the

Atlas and the Odontoid Process of the Axis.

the lateral mass of the atlas. It is arched backwards behind the Lontoid process, and at the median line it is connected on the posterior pect with the limbs of the vertical portion of the cruciate ligament, etween the ligament and the odontoid process there is an extensive novial membrane, which extends well over each lateral aspect of Le process, so as to come very near another synovial membrane Tween the front of the process and the anterior aich of the atlas.

The capsular ligaments are loose sacs which surround the aiticulaons between the inferior articular processes of the atlas and the

iperior articular processes of the axis.

The accessory ligament on each side extends from the posterior irface of the body of the axis, close to the root of the odontoid projss, to the inner and posterior part of the lateral mass of the a as ee Fig. 857). The direction of each ligament is upwards and out


A MANUAL OF ANATOMY


1406


wards, and it is closely related superiorly to the capsular ligamen which it strengthens internally and posteriorly. The accessory lig ments are auxiliary in function to the alar ligaments, and limit rotatic of the atlas upon the axis.

The uppermost part of the anterior longitudinal ligament (anterii atlanto-axial ligament), broad, thin, and membranous, is attache superiorly along the lower margin of the anterior arch of the atla and interiorly to the anterior aspect of the body of the axis. It continuous below with the anterior longitudinal ligament of the bodi< of the vertebrae, and its central portion is rendered thick by accessoi fibres derived from that ligament.

The posterior atlanto-axial ligament, also broad, thin, and men branous, extends from the under aspect of the posterior arch of tl atlas to the upper borders and adjacent portions of the outer surfac<


External Occipital Crest


Posterior Atlanto-occipital Membrane


Fig. 856. —The Occipital, Atlantal, and Axial Ligaments (Superficial Posterior View).


of the laminae of the axis. It is serially continuous with, and reprt sents, the ligamenta subflava of succeeding vertebrae.

Atlanto-occipital Joints. —These belong to the class of synovis joints of the condyloid type. The articular surfaces are the condyle of the occipital bone and the superior articular processes of the atlas Ligaments. —These are the capsular ligaments and the anteric and posterior atlanto-occipital membranes, the latter two being ir directly connected with the joints.

The capsular ligaments are loose sacs which directly surroun the articulations. Their fibres are attached superiorly round tb margins of the occipital condyles, and inferiorly to the lateral masse of the atlas round the superior articular processes.

The anterior atlanto-occipital membrane, thin and membranous, i attached inferiorly to the upper margin of the anterior arch of tb















THE HEAD AND NECK


I 4°7


tlas, and superiorly to the under surface of the basilar part of the capital bone, close to the front part of the foramen magnum, between he occipital condyles. In the median line it is thickened by fibres diich are attached below to the tubercle on the anterior arch of the tlas, but some of them are prolonged into the thickened part of the nterior longitudinal ligament.

The posterior atlanto-occipital membrane, broad, thin, and memiranous, is attached inferiorly to the upper margin of the posterior rch of the atlas, except in the region of the vertebrarterial grooves, nd superiorly to the lower margin of the foramen magnum behind he occipital condyles. Over each vertebrarterial groove of the atlas his ligament forms an arch which is sometimes ossified (see p. 131), nd beneath which the vertebral artery and suboccipital nerve pass.


MembranajTectoria


Basilar Groove of Occipital Bone v /

\ /

AlarLigameut\ ^'• ' A


Superior Longitudinal Band of Cruciate Ligament


/iav- Sm ,


Transverse Ligament of Atlas


Accessory

Atlanto-axial

Ligament


Atlanto -occipital

Capsule


-Atlanto-axial

Joint

(opened)


Inferior Longitudinal Band of Cruciate Ligament

Spine of Axis

'ig. 857. —Occipital, Atlantal, and Axial Ligaments (Posterior View).


Occipito-axial Ligaments. —These are the membrana tectoria; the lar ligaments; the apical ligament; and the vertical portion of the ruciate ligament.

The membrana tectoria (posterior occipito - axial ligament) is a

>road membranous band which is attached inferiorly to the posterior urface of the body of the axis, where it is continuous with the fibres I the posterior longitudinal ligament of the bodies of the vertebrae, nd superiorly to the posterior part of the basilar groove of the ccipital bone. It covers the odontoid process of the axis and the lar and cruciate ligaments.

The vertical portion of the cruciate ligament consists of superior Ind inferior longitudinal bands. Ihe superior band extends from the •osterior surface of the transverse ligament of the atlas at the mid






1408


A MANUAL OF ANATOMY


line to the posterior part of the basilar groove of the occipital bone between the anterior margin of the foramen magnum and the uppei attachment of the membrana tectoria, under cover of which it lies This band, as it ascends, is in contact with the posterior surface oj the head of the odontoid process. The inferior band extends from the posterior surface of the transverse ligament of the atlas at the mid-line to the posterior surface of the body of the axis above the inferior attachment of the membrana tectoria.

The transverse portion of the cruciate ligament is the transverse ligament of the atlas, already described.

The apical ligament of the odontoid process (middle odontoid ligament) is a narrow round cord which is attached below to the ridge oi


Membrana Tectoria

Superior Longitudinal Band of

Cruciate Ligament . N 1,11 A .in


Anterior Margin of Foramen Magnum \ Odontoid Process of Axis


Basilar Groove of Occipital Bone / Apical Ligament


Anterior Condylar Canal Alar Ligament


Atlantooccipital J oin t (capsule)


Atlanto-axial Joint(opened)


Spine of Axis


Fig. 858. The Occipital, Atlantal, and Axial Ligaments (Deep

Posterior View).


the head of the odontoid process, and above to the anterior margin of the foramen magnum in the mid-line.

This structure has little or no ligamentous function, but is a remnant of the notochordal sheath.


The alar ligaments of the odontoid process (check ligaments)

form two very strong bands which are attached medially to the lateral surfaces on the head of the odontoid process, and laterally to an impression on the inner surface of each condylar part of the occipital bone. The direction of each ligament is outwards and slightly upwards.

Movements-—Atlanto-axial Joints. —The atlas, bearing the head, rotates on the axis, the odontoid process of which serves as a pivot. The extent of rotation is about 30 degrees, and is limited by the alar, aided slightly by the accessory atlanto-axial ligaments. On p. 130 it has been seen that the superior


/



















THE HEAD AND NECK


I 4°9


icular processes of the axis are each divided by a slight transverse impression o two parts—anterior and posterior. When the face is directed straight wards, the inferior articular processes of the atlas are not in accurate contact th the superior articular processes of the axis. Between the contiguous pairs nre is a distinct interval all round. When, however, the atlas is rotated, the terior division of the axial articular process of one side is brought into accurate itact with the corresponding atlantal articular process, and the posterior nsion of the opposite axial articular process into accurate contact with the antal articular process of that side.

Atlanto-occipital Joints. —The movements allowed at these joints are flexion, tension, and oblique movement. Flexion and extension constitute the forward d backward, or nodding, movements. In over-extension (dorsi-flexion) the s terior margins of the superior articular processes of the atlas enter the condylar see of the occipital bone, and locking takes place. In complete forward or ntral flexion the anterior margins of the superior articular processes of the as come into contact with the occipital bone in front of each condyle.


89


CHAPTER XV

THE NERVOUS SYSTEM


The nervous system is arranged in two main divisions, cerebro-spina and autonomic; this last contains the sympathetic and the parasym pathetic.

The sympathetic system consists of two gangliated cords situate* on either side of the vertebral column, and three main prevertebra plexuses: the cardiac situated in the thorax; the epigastric or solar and the hypogastric plexus, the latter two being situated in th abdomen; subsidiary plexuses are associated with these.

The parasympathetic system includes cranial and sacral outflows leaving the cerebro-spinal axis through certain nerves without joininj the sympathetic cords.

The cerebro-spinal nervous sytem or axis consists of the encephaloi and the spinal cord, the former being situated within the crania cavity, and the latter within the spinal canal. The continuity betwee; these two divisions is established through the foramen magnum.

The cerebro-spinal axis is central in position, and is connecte* with the various parts of the body by the cranial and spinal nerves It is composed of two kinds of nervous matter, white and grey. Th white matter consists chiefly of nerve-fibres, and the grey matter c nerve-cells, with their axis-cylinder processes or axons and dendrites the pervading supporting tissue in each case being called neuroglk In the spinal cord the white matter is disposed externally, whilst th grey matter is situated in the interior. In the brain there is the sam arrangement of grey matter in the centre, surrounded by white mattei but a third and more modern layer of cortical grey matter has bee added to the surface of the white, a layer which is unrepresented i the spinal cord.

The cerebro-spinal axis is surrounded by three membranes, c meninges , which, from without inwards, are named the dura matei arachnoid membrane, and pia mater.


THE SPINAL CORD.

Membranes of the Spinal Cord. —The membranes are three: th dura mater, the arachnoid membrane, and the pia mater.

Dura Mater. —This is the most external covering of the cord. I forms a dense fibrous tube, known as the theca, which extends fror the margin of the foramen magnum of the occipital bone to the lowe level of the second sacral vertebra. Inferiorly, where it has becom

1410 1


THE NERVOUS SYSTEM


1411


Frontal Lobe


Temporal Lobe

/. Basilar Artery Vertebral Arteries


[■six


j -— Superior Cervical Sympathetic / Ganglion


1>. Cervical Plexus

■j -Vertebral Artery

i-Middle Cervical Ganglion

Brachial Plexus ist Thoracic Ganglion


4th Intercostal Nerve Anterior Spinal Artery


U_ Thoracic Sympathetic Cord




. Spinal Ganglion


Subcostal Nerve


L-. Lumbar Sympathetic Cord


Lumbar Plexus


Pelvic Sympathetic Cord


^— Sacral Plexus


Ganglion Impar


Eig. 859.—The Cerebrospinal and Sympathetic Systems (Anterior

View) (Hirschfeld and Leveille).



















1412


A MANUAL OF ANATOMY


tapering behind the second sacral vertebra, the theca is perforate by the filum terminale, and from this level the spinal dura mater i prolonged downwards around the filum terminale, with which it blend: Finally, it is attached, along with the filum terminale, to the bac of the first coccygeal vertebra, where it is incorporated with th periosteum. In this situation the spinal dura mater is firmly fixed.

The theca surrounds the spinal cord very loosely, and it is separate from the wall of the spinal canal by an interval, called the extra-dur; space, which is occupied by venous plexuses and loose areolar tissue.

Opposite the intervertebral foramina of each side the theca has series of openings, which are arranged in two parallel rows. Th openings constituting each pair are placed side by side, but are distinc from each other, and they transmit the ventral or anterior and dors; or posterior roots of the spinal nerves. Each of these roots, as it make its exit, receives a tubular sheath from the margin of the corresponds thecal opening, and these sheaths remain distinct as far as the spin; ganglion of the dorsal root. After this the neighbouring sheath form one which blends with the sheath of the corresponding spin; nerve.

The spinal dura mater is maintained in position by several cor nections. (i) Superiorly it is fixed to the margin of the forame magnum of the occipital bone. (2) Opposite the body of the ax: it is firmly attached anteriorly ’ to the posterior occipito-axial ligamen (3) Below the level of the axis it is loosely connected anteriorly wit the posterior longitudinal ligament of the bodies of the vertebrae b fibrous bands. (4) Laterally it is connected with the sheaths of th spinal nerves by means of the tubular sheaths which it gives to th ventral and dorsal nerve-roots. (5) Inferiorly it blends with th periosteum over the back of the first coccygeal vertebra through th filum terminale. Posteriorly it is quite free from connections.

The spinal dura mater differs from the cranial dura mater in th following respects: (1) It is destitute of an outer or periosteal layei (2) it does not send septa into the spinal cord; and (3) it does nc contain venous sinuses.

Blood-supply of Spinal Dura Mater.—The arteries are derive from (1) the spinal branches of the vertebral, intercostal, and lumba arteries; and (2) the lateral sacral arteries, which are branches of th internal iliac artery.

Nerve-supply.—The nerves are partly spinal and partly sympatheth

Lymphatic Vessels.—There are no lymphatic vessels, their plac being taken by perivascular lymph-spaces in connection with th arteries.

Structure. —The spinal dura mater consists of fibrous tissue and some elast: tissue disposed in parallel longitudinal bundles. Its internal and extern; surfaces are covered by endothelial cells.

Subdural Space.—Between the spinal dura mater and the arachnoi there is a narrow cleft-like interval, which is known as the subduri space. It contains a small amount of fluid, and communicates freel


THE NERVOUS SYSTEM


T 4 X 3


Dura Mater (Theca)


—-Arachnoid


h the lymph-spaces or clefts in the sheaths of the spinal nerves, has, however, no communication with the subarachnoid space. Spinal Arachnoid Membrane.—This is a delicate transparent mbrane which loosely surrounds the spinal cord between the theca ernally and the pia mater internally. It is separated from the

ca by the subdural space, and from the pia mater by the sub.chnoid space. Superiorly it is continuous with the cranial arachd, and inferiorly it encloses the cauda equina. On either side it

ms sheaths for the processes of the ligamentum denticulatum as as the inner surface of » theca. The ventral and

sal roots of the spinal
ves also receive sheaths

m it, which accompany un through the openings the theca, but soon cease.

It is of practical importce to remember that the ichnoid membrane usually Is at the lower level of the iond sacral vertebra, and ver extends lower than the ird.

Subarachnoid Space (Ca- , m Subarachnoidale).—This l ice, which is wide, is uated, as stated, between s arachnoid and pia mater, contains cerebro-spinal

id, and its dorsal part is

ntinuous superiorly with Fig - 86 °- Portion of the Spinal Cord,

- rerebello rnednllarv cis- showing the Membranes, Ligamenta o LEiEDEiio-iiiEuuiiaiy Lis Denticulata, and Roots of the Spinal

"na of the cranial sub- Nerves.

ichnoid space, which com micates with the fourth ventricle by the ‘ foramen of Magendie,’ e median aperture of the roof.

The subarachnoid space is partially divided into two compartmts, ventral and dorsal, by ligamenta denticulata, which form inmplete lateral septa. The ventral roots of the spinal nerves traverse e ventral compartment, and the dorsal roots the dorsal compartsnt. The dorsal compartment is partially subdivided into two •rtions, right and left, by means of a third incomplete septum, called e posterior septum. This partition extends from the pia mater as crosses the dorsal median fissure of the spinal cord to the dorsal -rt of the arachnoid at the median line. All the compartments of


Ligamentum Denticulatum

-Anterior Nerve-Root

Posterior Nerve-Root Pia Mater


_ Spinal Cord


Anterior Nerve-Root (cut)


e subarachnoid space communicate freely with each other.

The subarachnoid space has no communication with the subdura ace.













1414


A MANUAL OF ANATOMY


Structure of the Arachnoid Membrane. —The arachnoid consists of fine fibrou tissue arranged in interlacing bundles, the intervals between these bundle being occupied by delicate cellular membranes. Several such layers, intimatel blended together, form the membrane.

Beneath the arachnoid, and constituting a part of it, there is a reticulum c subarachnoid trabeculce. These trabeculae consist, as in the case of the arachnoi proper, of fine fibrous tissue, but the intertrabecular spaces, instead of bein occupied by cellular membranes, contain cerebro-spinal fluid. The trabecula reticulum connects the arachnoid with the subjacent pia mater, and varie greatly in density in different parts.


Spinal Pia Mater.—This is the deepest membrane of the spins cord. It is definitely fibrous and very vascular, and closely invest

the cord. Superiorly it is con


A] Dura Mater (Theca)


. Linea Splendens


Ligamentum Denticulatuir.


Pia Mater


J_L \nterior Nerve-Root


Fig. 86i.—A Portion of the Spinal Cord (Anterior View).

The theca has been laid open, and the arachnoid membrane removed.


tinuous with the cranial pi mater, and inferiorly it is pro longed from the conus medul laris over the upper half of th intrathecal part of the filur terminate. On either side i forms tubular sheaths for th ventral and dorsal roots of th spinal nerves, which blend wit] the sheaths of the nerves.

Along the course of th ventral median fissure of th cord it sends a vascular fob into that fissure. Along th course of the dorsal medial fissure, over which it passes the neuroglial septum occupy ing that fissure is attached t< it. From the deep orifice o the pia mater several septa ar


prolonged into the cord, which carry with them portions of the glia sheath.

The pia mater is separated from the arachnoid by the subarach noid space, and opposite the dorsal median fissure of the cord it i connected with the dorsal part of the arachnoid by the posterio subarachnoid septum.

Blood-supply.—The pia mater derives its arteries from the anterio and posterior spinal arteries, and the neural branches of the latera spinal arteries.

Nerve-supply.—The nerves are derived from the sympathetic system


Structure. —The spinal pia mater consists of two layers—outer and innei The outer layer consists of fibrous tissue, which is disposed for the most part i] parallel longitudinal bundles. The inner layer consists of areolar tissue containing a great many bloodvessels, and its outer and inner surfaces are covered by endcj thelial cells. Between the two layers there are narrow cleft-like lymphati spaces, which communicate with the subarachnoid space, and with lymphati clefts around the arteries of the pia mater.









THE NERVOUS SYSTEM


1415


The spinal pia mater differs from the cranial pia mater in being icker and more adherent to the nervous matter. The greater thick:ss is due to the presence of the outer layer, the cranial pia mater presenting the inner layer of the spinal pia mater.

Linea Splendens.—The pia mater at times presents a glistening >pearance immediately in front of the ventral median fissure. This ea is known as the linea splendens, and it extends along the entire ngth of the cord and along the conus medullaris on to the filum rminale.

Ligamentum denticulatum is a band of pia mater which extends ong the spinal cord on each side opposite the corresponding lateral >lumn. It lies between the ventral and dorsal roots of the spinal irves, and extends from the margin of the foramen magnum to the wer end of the cord. It lies within the subarachnoid space, and


Dura Mater


Fig. 862._Diagram of a Transverse Section of the Spinal Cord

and its Membranes.


A.M.F. Anterior Median Fissure, with Process of Pia Mater P.M.F. Posterior Median Sulcus A.C. Anterior Column L.C. Lateral Column P.C. Posterior Column


A.R. Anterior Nerve-Root P.R. Posterior Nerve-Root G. Spinal Ganglion S.P. Spinal Nerve A.P.D. Anterior Primary Ramus P.P.D. Posterior Primary Ramus


irtially divides that space into two compartments—ventral and orsal

Internally it forms an uninterrupted band which is attached to le pia mater along the lateral column of the cord. Laterally it is enticulated. The denticulations (about twenty-one m number) carry ith them sheaths from the arachnoid, and their pointed outer ends re attached to the inner surface of the theca in the intervals between ich pair of openings for the exit of the ventral and dorsal nerve-roots, he topmost denticulation is at the foramen magnum, lying between le eleventh nerve and the vertebral artery; the lowest is e ween tie last thoracic and first lumbar nerves, at the first lumbar vertebral

iygl

The two ligamenta denticulata act as lateral supports to the spinal °rd. ,. ,

Structure— Each ligamentum denticulatum consists of fibrous tissue, which

continuous with the outer layer of the pia mater.





1416 A MANUAL OF ANATOMY

External Characters of the Spinal Cord. — The spinal cord, o medulla spinalis, which is somewhat cylindrical, is that division o the cerebro-spinal axis which is situated within the spinal canal. I extends from the lower margin of the foramen magnum in the occipita bone to about the level of the disc between the bodies of the firs and second lumbar vertebrae, and it is about 18 inches in length Superiorly it is continuous with the medulla oblongata, and inferiorh it terminates in a tapering portion, called the conus medullaris. Fron the lower end of this cone a slender, glistening thread, called tb

filum terminale, about io inche long, is continued downward between the bundles of lumbar sacral, and coccygeal nerve of either side, which constitut the cauda equina, to be attache< to the back of the first coccy geal segment.

The spinal cord is of smalle dimensions than the spina canal, and is therefore relieve* from pressure during the ordi nary movements of the verte bral column. It is surrounde* by the three membranes alread; described—the dura mater, th archnoid membrane, and th pia mater. Within its theca o dura mater the cord is sus pended by means of the liga menta denticulata, and th nerve - roots as they emerg through the openings in th theca.

The spinal cord varies ii shape in different regions. L the cervical region, as seen ii transverse section, it is trans versely oval, and is slights flattened from before backwards. In the thoracic region it is almos circular, but the transverse diameter exceeds the antero-posterior In the lumbar region it is still more circular than in the thoraci region.

The cord has two swellings, which are known as the cervical an* lumbar enlargements, and are associated with the numerous larg< nerve-trunks destined for the upper and lower limbs. The cervica enlargement extends from near the upper end of the cord to the secon* thoracic vertebra, and its breadth is greatest opposite the sixth cervica vertebra. The lumbar enlargement, which is less conspicuous thai


Fig. 863. —Lumbar and Sacral Portions of Spinal Canal, showing Lateral View of Conus Medullaris, Filum Terminale, and Theca (Testut).





THE NERVOUS SYSTEM


1417


he cervical, extends from the level of the tenth thoracic vertebra o the conus medullaris, and its breadth is greatest opposite the twelfth horacic vertebra.

Filum Terminale.—This delicate glistening thread lies in the nedian line between the lumbar, sacral, and coccygeal nerves of either side, which constitute the cauda equina, and it extends from the apex )f the conus medullaris to the back of the first coccygeal segment.

[t is about 10 inches in length. As low as the back of the body of

he second or third sacral segment it is situated within the theca,

Dut at that level it pierces the theca, from which it receives an investment, md then passes to be attached to the back of the first coccygeal segment, where it blends with the periosteum. The intrathecal portion is known as the filum terminale internum, and the extrathecal portion as the filum terminale externum.

Structure. —The filum terminale internum in its upper half consists of pia mater prolonged from the conus medullaris of the spinal cord. This encloses grey matter, within which, over about the upper third, there is a continuation of the central canal of the cord. The lower half consists chiefly of connective tissue. The filum terminale externum is a mere fibrous filament invested by a prolongation of the theca which blends with it. It is also composed of pia mater prolonged downwards from the conus medullaris, and reinforced by fibres derived from the lower portions of the ligamenta denticulata and linea splendens.

Its lower part is purely fibrous. Fig . 864 ._the terminal

Cauda EQuina.—This is situated witmn Part of the Spinal Cord,

the lower part of the theca. It consists and the Cauda Equina of the roots of the lumbar, sacral, and ~

coccygeal nerves of each side, which are arranged m the form o a leash, and the filum terminale lies in the median line between the two nerve-leashes. On account of the high origins of the individual nerves, relatively to the positions of the intervertebral foramina through which they pass, the direction of the nerves is almost vertical until they reach the level of their respective foramina o exi .

Fissures of the Spinal Cord.—The spinal cord, which is somewhat flattened in front and behind, is incompletely divided into two symmetrical halves by two median formations, anterior and posterior. The anterior median Assure extends into the cord for one-third of its thickness from before backwards, and it contains a o c o le pia



_ Linea Splendens


Cauda Equina Conus Medullaris


If


_Filum Terminale















1418


A MANUAL OF ANATOMY


mater. At the bottom of the fissure the transverse band of nervefibres, called the anterior white commissure , crosses between the two halves of the cord. The posterior median septum is not an actual fissure like the anterior, and does not contain a fold of the pia mater, but is a septum of neuroglia, which extends into the cord for about half its thickness from before backwards. The posterior grey commissure lies at the bottom of the septum. The anterior median fissure is a definite depression, but it is not so deep as the posterior septum.

The posterior septum is marked on the surface by a median sulcus.

Each half of the cord presents a groove along the line of entrance of the fasciculi of the posterior nerve-roots, called the postero-lateral sulcus, but there is no similar groove along the line of emergence of the fasciculi of the anterior nerve-roots, these being spread over an area of some breadth. By means of the postero-lateral sulcus on the one hand, and the area corresponding to the emergence of the fasciculi of the anterior nerve-roots on the other, each half of the spinal cord is divided superficially into three white columns—anterior, lateral, and posterior.

The anterior white column is situated between the anterior median fissure and the most lateral fasciculi of the anterior nerve-roots; the lateral white column is the area between the most lateral fasciculi of the anterior nerve-roots and the postero-lateral sulcus; and the posterior white column lies between the postero-lateral sulcus and the posterior median sulcus. Practically the anterior column represents the region in front of the anterior nerve-roots, the lateral column the region between the anterior and posterior nerve-roots, and the posterior column the region behind the posterior nerve-roots. According to some authorities there are only two columns—namely, antero-lateral and posterior, the former extending from the anterior median fissure to the postero-lateral sulcus, and representing the combined anterior and lateral columns.

In the cervical region the surface of each posterior white column presents a slight groove which is situated nearer the posterior median sulcus than the postero-lateral sulcus. This groove is called the posterior intermediate or paramedian furrow . It contains a septum of pia mater, and in this manner the posterior column of the cord is marked off into two tracts. The medial and smaller tract is called the fasciculus gracilis (postero-median column of Goll), and the lateral and larger is called the fasciculus cuneatus (Burdach’s column, posterolateral column). These two columns extend throughout the cord, but it is only above the level of the mid-thoracic region that they are separated from each other by a septum of pia mater, known as the posterior intermediate septum.

Origin of the Spinal Nerves.—There are thirty-one pairs of spinal nerves, which arise from the sides of the spinal cord. They are arranged in five groups on either side as follows: cervical, eight in number; thoracic, twelve ; lumbar, five ; sacral, five ; and coccygeal, one. Each spinal nerve is attached superficially to the cord by two roots, anterior


THE NERVOUS SYSTEM


1419


nd posterior, the posterior root being the larger of the two. The ortion of the cord from which each pair of spinal nerves arise is spoken f as a segment of the cord. Each root is ensheathed by tubular probations of the coverings of the cord—namely, the pia mater, arachnid, and dura mater, in this order from within outwards—and these heaths ultimately blend with the perineurium. The roots are separated rom each other by the lateral column of the cord and the ligamentum enticulatum, and they pass through separate openings in the theca of

ura mater.

The anterior roots are composed of efferent or motor fibres, and their asciculi emerge from the cord in an irregular manner, being spread ver an area corresponding in breadth to the caput of the anterior

A

2


?IG. 865.—Two Segments of the Spinal Cord, showing the Attachments of the Anterior and Posterior Nerve-Roots, and the Spinal Ganglia.

A, superior view; B, anterior view.

1, 1. Anterior Median Fissure 5 > 5 - Spinal Ganglion

2, 2. Posterior Median Sulcus 6, 6. Spinal Nerve

a, a. Anterior or Motor Nerve-Root 7 , 7 - Anterior Primary Ramus

4, 4. Posterior or Sensory Nerve-Root 8, 8. Posterior Primary Ramus

9, 9. Medial and Lateral Branches of Posterior Primary Ramus

horn of the grey matter in the interior. The posterior roots are composed of afferent or sensory fibres, and their fasciculi enter the cord in a straight line along the course of the postero-lateral sulcus. Each posterior root presents an oval swelling, called the spinal ganglion. These ganglia are for the most part situated in the intervertebral foramina, and immediately beyond each ganglion the anterior and posterior roots unite to form a spinal nerve, which is necessarily a mixed nerve, inasmuch as it is composed of afferent and efferent fibres.

Each spinal nerve breaks up into an anterior and a posterior primary yamus

The upper cervical nerve-roots are short, and pass almost horizontally outwards. The succeeding nerve-roots, however, gradually increase in length, and incline downwards as they pass outwards,











1420


A MANUAL OF ANATOMY


This downward inclination goes on increasing until it becomes almost vertical in the case of the lumbar, sacral, and coccygeal nerves, which constitute the cauda equina. From this disposition it follows that in the majority of cases the superficial origins of the spinal nerves are on a higher level than the intervertebral foramina through which they emerge from the spinal canal.

Relation of the Spines of Vertebrae to the Bodies and to the Origins of the Nerves. —In the case of the cervical and the eleventh and twelfth thoracic vertebra the extremities of the spinous processes correspond to the lower margins of the bodies of the respective vertebrae. In the case of the thoracic vertebra, from the first to the tenth inclusive, the extremity of each spinous process corresponds to some part of the body immediately below. In the case of the lumbar vertebrae the extremity of each spinous process corresponds to the centre of the body of its own vertebra.

Each cervical spinous process is nearly opposite the lower fasciculi of the roots of the nerve below. The spinous process of the seventh cervical vertebra (vertebra prominens) is opposite the roots of the first thoracic nerve. From the third to the tenth thoracic vertebrae the spinous processes correspond to the second root below. The eleventh thoracic spine corresponds to the first and second lumbar nerves. The twelfth thoracic spine corresponds to the third, fourth, and fifth lumbar nerves. The first lumbar spine corresponds to the first, second, and third sacral nerves. (Gowers, from an original investigation.)


Mode of distinguishing the Anterior and Posterior Surfaces of the Spinal Cord.—These surfaces may be recognized by attending to the following points:


Anterior Surface.

1. Linea splendens in median line,

especially in lower part.

2. Anterior spinal artery in

median line.

3. Fasciculi of anterior nerve roots spread over a wide area.

4. Presence of an anterior median

sulcus which can be opened.


Posterior Surface.

1. Ganglion on each posterior nerve root.

2. Arterial anastomotic chain behind and

in front of the posterior nerve-roots.

3. Fasciculi of posterior nerve-roots lie

in a straight line, and enter through postero-lateral sulcus.

4. Presence of a posterior median sulcus

which cannot be opened.

5. Presence of gracile and cuneate fasci culi in upper part.


Internal Structure of the Spinal Cord.—The spinal cord, as seen in transverse section, consists of a central portion composed of grey matter, and an external portion composed of white matter.

Grey Matter.—This is arranged in the form of two irregular crescents, the concavities of which are directed outwards, and the convexities inwards, the latter being connected across the middle line by the grey commissure. The arrangement has been likened to the letter )-(. The grey commissure lies at the bottom of the posterior median sulcus, and presents about its centre the minute opening of the central canal of the cord. The part of the commissure in front of this canal is known as the anterior grey commissure, and the part behind as the posterior grey commissure. In front of the anterior grey commissure there is a transverse band of white matter, called the anterior white


THE NERVOUS SYSTEM


1421


immissure, which lies at the bottom of the anterior median fissure, ach crescent of grey matter consists of two horns, anterior and osterior, the former being in front of, and the latter behind, the grey mnmissure. The anterior horn is broad and blunt, and it stops short f the surface of the cord, being separated from the surface by white latter which is traversed by the fasciculi of the anterior nerve-roots, he blunt extremity of the anterior horn is called the caput cornu, and le portion adjoining the grey commissure, which is slightly constricted,

called the cervix cornu. The posterior horn is for the most part

mg, narrow, and tapering, and its pointed extremity almost reaches tie surface of the cord at the bottom of the postero-lateral sulcus, 'his pointed extremity is called the apex cornu, and it contains a transient substance, known as the substantia gelatinosa (of Rolando), diich forms the cap for the caput cornu posterioris. It contains a


Central Canal


?i G . 866._ Transverse Section of the Spinal Cord in the Upper Thoracic

Region, showing the Arrangement of the Grey Matter and Cells (Semi-diagrammatic) (after Poirier).

small amount of neuroglia, and numerous nerve-cells. The portion idjoining the grey commissure, which is slightly constricted, is called the cervix cornu, and the portion contiguous to the cervix, w 11c is slightly enlarged, is called the caput cornu. The part between the

two cornua is called the body. ' ,

About the centre of the concavity of the body crescent the grey

matter projects into the lateral column in the form of processes arranged in a reticular manner and enclosing white matter. This network is sailed the processus reticularis, and it is most conspicuous m the cervical region. In the thoracic region, more particular y in 1 s uppei part, the grey matter of each crescent forms a triangular projection which extends laterally for a short distance immediately m front of the processus reticularis, and adjacent to the junction o e an erior

ornu with the grey commissure. This projection is known as the







1422


A MANUAL OF ANATOMY


lateral horn. When followed into the lower cervical and into the lumbar regions it blends with the anterior horn, the thickness of which it increases, but it is again present above the level of the fourth cervical vertebra.

The grey matter has been described, so far, as it would be seen on looking at transverse sections through the cord; under such conditions the use of the term ' horn ’ or ' cornu * is quite appropriate. As it exists in the complete cord, however, the grey matter is in the form of a continuous column , and in considering it in such a way it should be described as possessing anterior, posterior, and lateral ' columns,’ rather than ‘ horns.’

The grey matter varies in amount in different parts of the cord. It is present in largest quantity in the lumbar enlargement, where the large nerve-trunks for the lower limbs arise, and next to this in the cervical enlargement, where the large nerve-trunks for the upper limbs arise.

The horns of the crescents of grey matter vary in shape, as seen on section, in different regions. In the cervical region the anterior


A


Fig. 867. —Transverse Sections of the Spinal Cord in Different

Regions.

A, cervical region; B, mid-thoracic region; C, lumbar region; D, conus

medullaris.

horns are short, broad, and blunt, and the posterior horns are long, narrow, and pointed. In the thoracic region both horns are narrow, though the posterior is more so than the anterior. In the lumbar region both are broad, though the anterior is more so than the posterior. These differences render sections of the spinal cord in the cervical, thoracic, and lumbar regions easily recognizable. As stated, the lateral horn is also a characteristic of the cord in the thoracic region, more particularly in its upper part.

Central Canal.—This minute canal is situated about the centre of the grey commissure, and extends throughout the entire length of the spinal cord. Superiorly it is continued into the lower half of the medulla oblongata, and it opens into the lower part of the fourth ventricle at the calamus scriptorius. Interiorly, near the apex of the conus medullaris it becomes enlarged, and assumes the shape of an inverted ±. This enlargement is known as the ventriculus terminalis. From this point it is prolonged for some distance into the filum terminale, and it ends in a closed extremity. In the cervical and thoracic regions the central canal is nearer the anterior surface of the cord than the













THE NERVOUS SYSTEM


i 4 2 3


sterior, but in the lumbar region it occupies the centre. In the aus medullaris it is near the posterior surface.

The canal is lined with ciliated columnar epithelium, the columnar Is being known as ependymal cells.

The central canal represents the lumen of the neural tube of ectoderm from ich the spinal cord is developed.

White Matter of the Spinal Cord.—The white matter forms the ter part of the cord, and is arranged in three columns—anterior, teral, and posterior. The anterior column is situated between the iterior median fissure and the anterior horn of grey matter, and tends as far as the most lateral fasciculi of the anterior nerve-roots, therefore includes the superficial coating of the anterior horn, where is traversed, over an area of some breadth, by the scattered fasciculi the anterior nerve-roots. The lateral column is situated between the iterior and posterior horns of grey matter, in the concavity of the escent. Its superficial limits are the most lateral fasciculi of the iterior nerve-roots and the fasciculi of the posterior nerve-roots at e postero-lateral sulcus. The posterior column is situated between e posterior median sulcus and the posterior horn of grey matter, its perficial limit being the fasciculi of the posterior nerve-roots at the >stero-lateral sulcus.

The white matter increases in quantity from below upwards, and pta of pia mater and neuroglia fibres pass into it at various points.


Jhief Distinguishing Characters of the Spinal Cord in Different Regions, as

seen in Transverse Sections.


Cervical Region.

Transversely oval.

Anterior Horn, short, broad, and blunt.

Posterior Horn, long, narrow, and tapering.

Formatio Reticularis, well marked.

Lateral Horn, merged into anterior, except above fourth cervical vertebra.

White Matter, large in amount.


Central Canal, nearer the ventral than the dorsal surface.

Postero - intermediate Sulcus and Septum of pia mater, well marked.


Thoracic Region.

1. Circular.

2. Anterior and Posterior

Horns, both narrow, posterior more so than anterior.

3. Formatio Reticularis,

not very distinct.

4. Lateral Horn, con spicuous, especially in upper part

5. White Matter, less in

amount, but large in proportion to Grey Matter.

6. Central Canal, nearer

the ventral than the dorsal surface.

7. Postero - intermediate

Sulcus, absent, but Septum of pia mater recognizable.


Lumbar Region.

1. Almost circular.

2. Anterior and Posterior

Horns, both broad, anterior more so than posterior.

3. Formatio Reticularis,

absent.

4. Lateral Horn, merged

into anterior.


5. White Matter, small

in amount, and Grey Matter, large.

6. Central Canal, in the

centre.


7. Postero - intermediate Sulcus and Septum of pia mater, absent.


I 4 2 4


A MANUAL OF ANATOMY


Minute Structure of the Spinal Cord—Grey Matter.—The grey matter consists of nerve-cells, nerve-fibres, and neuroglia, and is very vascular.

The nerve-cells are present in great numbers, and are multipolar. Each cell sends off at various points several protoplasmic processes, one of which becomes the axis-cylinder of a nerve-fibre, and is called the axis-cylinder process, or axon. The other processes are known as the protoplasmic processes {of Deiters), or dendrites, and, after successive branchings, they terminate in free extremities. There are no anastomoses between the dendrites of the same cell, nor between those of contiguous cells. A multipolar nerve-cell, with its axon and dendrites, constitutes a neuron. The multipolar cells form longitudinal columns of various lengths, and, as seen in transverse sections of the cord, they are arranged in groups which occupy particular regions. These

Central Canal


Fig. 868.— Transverse Section of the Spinal Cord in the Upper Thoracic Region, showing the Arrangement of the Grey Matter and Cells (Semi-diagrammatic) (after Poirier).

cell-columns or groups are three in number—namely, anterior or ventral, in the anterior horn of grey matter; lateral, in the lateral horn of grey matter; and posterior, constituting the thoracic nucleus (or posterior vesicular column of Lockhart Clarke), and being very conspicuous in the medial portion of the cervix of the posterior grey horn in the thoracic region. Besides these main columns or groups, other nerve-cells are present, which are scattered irregularly throughout the other portions of the grey matter.

The anterior or ventral cell-column is situated, as stated, in the anterior horn of grey matter, and extends throughout the whole length of the spinal cord. Its cells are of large size and very conspicuous, and their axons, which are at first non-medullated, become medullated, and then constitute the fasciculi which emerge to form the anterior nerve-roots. These cells are therefore the sources from which the






THE NERVOUS SYSTEM


  • 4 25


Trent or motor nerve-fibres proceed, and the ventral column is nsequently spoken of as the motor column. The ventral or motor 11 s of this column are arranged in two groups, medial and lateral, re medial group occupies the medial part of the anterior grey horn, id the lateral group is situated in its outer part. In the cervical and mbar enlargements of the cord the cells of the lateral group are very imerous, and are arranged in two sub-groups, ventro-lateral and )rso-lateral.

The intermedio-lateral cell-column is situated, as stated, in the teral horn of grey matter, and the cells constitute a column known

the intermedio-lateral nucleus.

The thoracic cell-column is situated in the medial part of the

rvix of the dorsal cornu of grey matter. This extends throughout

le entire thoracic region of the cord, and for a short distance into le cervical and lumbar enlargements. The cells make an elongated jcleus (often termed Clarke’s column), and are of large size. This )lumn exists chiefly in the thoracic portion of the cord, whence the ime thoracic nucleus.

The cells of the grey matter differ as regards their axons, some having short, id others long, axons.

The cells with short axons have their axons confined to the grey matter, which they ramify not far from the parent-cells. They serve to bring contiguis cells into relation with one another.

The cells with long axons are partly root-cells and partly association-cells^ id their axons travel for some distance from the parent-cells. The axons of le root-cells leave the cord in the fibres of the ventral or motor nerve-roots, he axons of the association-cells constitute association-fibres, which are disused in two ways: (1) Some enter the white matter of the same side of the >rd, in which they divide into ascending and descending branches. Eventually iey re-enter the grey matter, and terminate in arborizations at some distance om the parent-cells. (2) Other association-fibres cross to the opposite side 1 the ventral or white commissure. Some of these end in arborizations around le cells of the grey crescent, whilst others enter the white matter, in which ley are disposed as on the side from which they have crossed.

Destination of Axons of Cells of Grey Matter.

Cells of Ventral Horn. —(1) Many axons become the axis-cylinder processes f the efferent fibres of the ventral nerve-roots. (2) Other axons constitute ssociation-fibres, which cross to the opposite side in the ventral 01 white comlissure. After crossing, some end in arborizations around the cells of the entral horn * others enter the white matter; and a few are regarded by some uthorities as entering the ventral nerve-roots of the side to which they have rossed

Cells Of Lateral Horn.—The axons of the cells of the intermedio-lateral nucleus ass to the efferent fibres of the ventral nerve-roots, and they are regarded as irnishing the white rami communicantes of the sympathetic system.

Cells Of Dorsal Horn. —The axons of the cells of the dorsal horn have various irections; (1) Some pass to the ventral horn and ventral 01 white commissure. >) The axons of the cells of the thoracic nucleus pass to the lateral column, and re usually regarded as entering the dorsal cerebellar and ventro-lateral cereellar tracts. (3) The axons of the cells of the substantia gelatmosa pass partly 3 the lateral column, adjacent to the dorsal horn, where they divide into ascenc ig and descending branches, and partly into the posterior marginal bun e o

90


1426


A MANUAL OF ANATOMY


Lissauer. (4) The axons of other cells in the lateral part of the cervix of tb dorsal horn pass to the lateral and ventral horns, the ventral or white commissure and the lateral column. (5) The axons of the cells of the caput cornu posteriori pass to the lateral column of the same side, and a few are regarded as passinj to the opposite side in the ventral or white commissure.

Dorsal or Grey Commissure. —This commissure lies at the bottoir of the dorsal median septum. It consists of (1) grey matter, con taining a few small nerve-cells, and (2) medullated nerve-fibres. Thes( fibres pass across from one side to the other, and later on diverge ir each grey crescent. They serve as association fibres which bring th( cells of opposite sides into relation with one another. This commissun contains the central canal of the cord, which for the most part is nearei the ventral portion of the commissure than the dorsal. The part o: the commissure surrounding the central canal is called the substantia gelatinosa centralis. It consists of neuroglia, a few nerve-cells, anc nerve-fibres; and it is invaded by processes derived from the deep end. c of the ciliated columnar epithelial cells which line the central canal.

Summary of the Gelatinous Substances of the Grey Matter. — These are

(1) The substantia gelatinosa, which forms a cap for the caput cornu posterioris :

(2) the substantia gelatinosa centralis, which surrounds the central canal ©f the cord; and (3) the substantia gelatinosa externa, which forms the glial sheath oj the cord beneath the pia mater.

White Matter. —The white matter of the cord consists of longitudinal medullated nerve-fibres, traversed by septa of the pia mater, and embedded in neuroglia. The fibres have no primitive sheath or neurilemma.

Ventral or White Commissure. —This commissure lies at the bottom of the ventral median fissure, and it is separated from the central canal of the cord by a part of the dorsal or grey commissure. It consists ol medullated nerve-fibres, destitute of a neurilemma, some of which pass transversely, but most of them decussate, entering the commissure ventrally on one side, and leaving it dorsally on the opposite side. The fibres, after crossing, enter the grey crescent and the ventral column. They are derived from (1) the anterior cerebro-spinal tract, (2) the processes of root-cells and of association cells, and (3) the fibres of the spino-thalamic tract, to be presently described.

Fibres of Roots of Spinal Nerves—Ventral or Anterior NerveRoots. —The fibres of the ventral nerve-roots arise within the cord from several sources. (1) Many of them are axons of the medial cells of the ventral horn of grey matter of the same side. (2) Some are axons of the lateral cells of the ventral horn. (3) Others are axons of the cells of the thoracic nucleus of the same side. (4) A few are axons of cells in the dorsal horn of grey matter of the same side. (5) A few are regarded as being axons of the medial cells of the ventral and intermediate grey matter of the opposite side , which cross in the ventral or white commissure. All the axons receive their medullary sheaths near the parent cells, and they form funiculi, which leave the white matter of the ventral column over an area corresponding to the caput


THE NERVOUS SYSTEM


1427


the ventral horn of grey matter, after which each fibre acquires its imitive sheath or neurilemma.

Most of the axons of the fibres of the ventral nerve-roots belong to the ntral (motor) cells of the ventral horn of grey matter of the same side.

Dorsal or Posterior Nerve-Roots.—The fibres of the dorsal nerveots arise from the unipolar (orginally bipolar) cells of the spinal nglia. The single pole or process of each of these cells is T-shaped, le half of the horizontal limb of the T is central, and enters the cord



' IG . 869.— Course of Nerve-Fibres in the Spinal Cord (from Halliburton’s

  • Handbook of Physiology ’ (after Schafer).


P. Cerebro-spinal Tract 1, 2, 3, 4. Anterior Cornual Cells K, A, A, A. Axons of Anterior Cornual Cells M. Muscular Fibre

G. Unipolar Cell of a Spinal Ganglion, giving Origin to a Fibre of a Posterior NerveRoot

B. Peripheral Branch of Fibre S. Skin . .

(lowerC) Central Branch of Fibre, passing into the Spinal Cord

. Descending Branch of Fibre in the Spinal Cord


D. Ascending Branch of Fibre in the Spinal Cord Pi, P2. Posterior Cornual Cells

C (upper C). Cell of Clarke’s Column or Thoracic

Nucleus .

5. Collateral, passing directly to arborize around an

Anterior Cornual Cell (2). >

6. Collateral, with an Intermediate Cell-Station in a

Posterior Cornual Cell (P 2 ).

7. Collateral, arborizing around a Cell ot Clarke s

Column (upper C). ,

8. Continuation of Main Ascending Branch of Fibre.


the dorso-lateral sulcus between the dorsal and lateral coiumns of ilte matter. The other half of the horizontal limb is peripheral, and

sses outwards in the course of the nerve. • ol K 11 n f

Within the cord a few lateral fibres enter the marginal bundle 3sauer, and the dorsal horn of grey matter, but most of them pass -o th e poslero-lateral column (Burdach) close to the dorsal horn of

y matter. Within this column the fibres divide into ^ branches

lending and descending. The descending branches, after a short





1428


A MANUAL OF ANATOMY


course, enter the dorsal horn. These descending fibres are usualh regarded as forming the ‘ comma tract.’ The ascending branches are longer than the descending, and, at various levels, they also enter the dorsal horn. The ascending branches of the fibres of the dorsal roots of the lower spinal nerves enter the postero-medial column.

The ascending and descending branches give off numerous collateral fibrils, which enter the dorsal grey column. These collaterals have the following destinations: (1) The dorsal horn of the same side, and that of the opposite side through the dorsal or grey commissure; and (2) the ventral and lateral horns of the same side. In each case they

come into close relation with the corresponding nerve-cells_ e.g., the

cells of the dorsal horn, including the thoracic nucleus, the ventral or motor cells of the ventral horn, and the cells of the thoracic nucleus in the lateral horn.


Sensory Fibres entering Fasciculus Cuneatus (Burdach) Cells of Posterior Column and Thoracic Nucleus ' Posterior Ro<


Spinal Ganglia. — these are situated on the posterior roots of the spinal nerves in the intervertebral foramina, and outside the theca, though invested by a prolongation from it. Each ganglion is oval, and consists of unipolar nerve-cells. The single pole of each cell divides into two processes, one of which is centripetal and forms part of the posterior nerve-root, whilst the other is centrifugal and passes into the spinal nerve. The pole and its inward and outward processes resemble the letter T. In early life the cells are bipolar.

The fibres of the posterior nerve-roots have their deep origins in the unipolar cells of the spinal ganglia, and they grow into the spinal cord. On the other hand, the fibres of the anterior nerve-roots have their deep origins within the spinal cord, where they arise as the axons of the multipolar nerve-cells of the anterior column of grey matter, and they grow outwards.




THE NERVOUS SYSTEM


1429


Tracts of the Spinal Cord.

Posterior Column. —The tracts of this column are ascending and xending, and they are as follows:

Ascending Tracts. Descending Tracts

Fasciculus gracilis (Fig. 871, 1). Semilunar (comma) tract (Fig. 871, 9). Fasc. cuneatus (Fig. 871, 2). Septo-marginal bundle (Fig. 871, 10).

Postero-lateral tract (of Lissauer)

(Fig. 871, 3).

Lissauer’s tract also belongs to the lateral column.


19

Descending


Ascending.


F IG . 871.— The Tracts of the Spinal Cord.


Ascending.

Fasciculus gracilis (Goll’s column).

. Fasciculus cuneatus (Burdach’s column).

Fasciculus postero-lateralis (Lissauer’s tract). _

|.. Posterior spino-cerebellar fasciculus (Flechsig’s tract).

5. Anterior spino-cerebellar fasciculus (Gower’s tract).

5 . Lateral spino-thalamic tract.

7. Anterior spino-thalamic tract.

1 . Intersegmental tract (fasciculus proprius: ground bundle).


Descending.

9. Semilunar (or comma) tract.

10. Septo-marginal bundle.

n. Lateral cerebro-spinal fasciculus (crossed pyramidal tract).

12. Anterior cerebro-spinal fasciculus (direct pyra midal tract).

13. Lateral intersegmental tract.

14. Anterior intersegmental tract.

15. Sulco-marginal tract.

16. Rubro-spinal tract (Monakow’s bundle).

17. Tecto-spinal tract.

18. Olivo-spinal tract (Helweg’s tract).

19. Vestibulo-spinal tract.


Ascending Tracts. —The fasciculus gracilis (tract of Goll) is situated ose to the posterior median septum. Its fibres are derived from the orsal roots of the coccygeal, sacral, lumbar, and lowei thoracic nerves, hey are at first contained in the cuneate tract, but as they ascend ley are gradually displaced medially, and so foim a special tract, he fibres terminate superiorly in connection with the cells of the

ucleus gracilis of the medulla oblongata.

The fasciculus cuneatus (tract of Burdach) is situated on the lateial ide of the tract of Goll next to the dorsal horn of grey mattei.











1430


A MANUAL OF ANATOMY


Above the mid-thoracic region it is separated from Goll’s tract by the dorsal intermediate or paramedian furrow and a septum of pia mater. Its fibres are derived from the dorsal nerve-roots. Above the mid-thoracic region they are derived from the dorsal roots of the upper thoracic and cervical spinal nerves, and these fibres terminate superiorly in connection with the cells of the nucleus cuneatus of the medulla oblongata. Below the mid-thoracic region the fibres are derived from the lower dorsal nerve-roots, and these, being displaced inwards into the gracile tract, terminate in connection with the cells of the nucleus gracilis.

The postero-lateral fasciculus (Lissauer’s tract) is close to the outer surface of the cord. It embraces the contiguous parts of the posterior and lateral columns, and occupies the region of the dorso-lateral sulcus where the funiculi of the dorsal nerve-roots enter the cord. It lies between the substantia gelatinosa and the surface of the cord. Its fibres are derived from the dorsal nerve-roots, and they ascend close to the substantia gelatinosa , in which they terminate at different levels.

Descending Tract.—The semilunar tract (comma) is situated in the cuneate fasciculus. Its fibres are usually regarded as being derived from the descending branches of the fibres of the dorsal nerve-roots, in which case they are exogenous. The other view, however, is that the fibres are intrinsic or endogenous, and spring from the cells of the dorsal cornu of grey matter.

Antero-lateral Column,—1 he tracts of this column are arranged into descending and ascending, and are as follows:


Descending Tracts.

1. Lateral cerebro-spinal (crossed pyra midal) tract (Fig. 871, 11).

2. Anterior cerebro-spinal (direct pyra midal) tract (Fig. 871, 12).

3. Intersegmental tract (Fig. 871, 13 and

14).

4. Rubrospinal tract (Fig. 871, 16).

5. Vestibulo-spinal tract (Fig. 871, 19).

6. Olivo-spinal tract (Fig. 871, 18).

7. Tecto-spinal tract (Fig. 871, 17).


Ascending Tracts.

1. Dorsal spino-cerebellar tract

(Fig. 871, 4).

2. Ventral spino-cerebellar tract

(Fig. 871, 5).

3. Anterior spino-thalamic tract

(Fig. 871, 7).

4. Lateral spino-thalamic tract

(Fig. 871, 6).

5. Spino-tectal tract (Fig. 871, 6).


Descending Tracts.—The crossed pyramidal or lateral cerebro-spinal tract (fasciculus spinalis lateralis, Fig. 871, 11) is a long descending tract of large size, which is situated deeply in the dorsal part of the lateral column directly in front of the dorsal cornu of grey matter. It is separated from the outer surface of the cord by the dorsal spinocerebellar (or direct cerebellar) tract. It diminishes in size as it descends, and in the lumbar region it becomes superficial. At about the level of the third sacral nerve it ends. The fibres of this tract have their origin in the pyramidal cells of the motor area of the cortex of the cerebral hemisphere of the opposite side. From this origin they descend through (1) the internal capsule of the corpus striatum, (2) the crus


THE NERVOUS SYSTEM


i43i


srebri, and (3) the pons. On leaving the pons they enter the pyramid f the medulla oblongata on the side from which they have arisen, t the lower part of the pyramid they cross to the opposite side and ike up their position deeply in the dorsal part of the lateral column f the spinal cord. The fibres of the crossed pyramidal tract of one de therefore come from the cerebral hemisphere of the opposite side, nd they form the inner and larger part of the pyramid of the medulla blongata, also of the opposite side. As this tract descends, fibres

ave it in each segment of the cord. These fibres enter the ventral

orn of grey matter, and end in close relation with the ventral or lotor cells, the axons of many of which form the axis-cylinder prossses of the fibres of the ventral or motor nerve-roots.

The direct pyramidal or anterior cerebro-spinal tract is of small size, nd is situated in the anterior column, where it lies close to the ventral ledian fissure. It diminishes in size as it descends, and usually srminates about the centre of the thoracic region, but fibres have been raced as low as the fourth sacral nerve. The fibres of this tract, like lose of the crossed pyramidal tract, have their origin in the pyramidal ills of the motor area of the cortex of the cerebral hemisphere, but in his case of the same side. The fibres of the direct pyramidal tract of ne side therefore come from the cerebral hemisphere of the same side, hey pursue a similar downward path as low as the pyramid of the ledulla oblongata of the same side, of which they form the smaller art. They take no part, however, in the decussation of the pyramids, s do the fibres of the crossed pyramidal tract. Their course is directly ownwards into the corresponding half of the spinal cord, where most fthem take up their position in the anterior column close to the ventral ledian fissure. The fibres of the direct pyramidal tract, though they ike no part in the decussation of the pyramids, cross to the opposite ide at regular intervals as they descend in the anterior column of tie cord. The crossing takes place in the ventral or white commissure, nd, having entered the ventral horn of grey matter of the opposite ide, the fibres end, like those of the crossed pyramidal tract of that ide, in close relation with the ventral or motor cells, the axons of lany of which pass to the ventral or motor nerve-roots.

Most of the pyramidal fibres therefore cross from the side on which hey arise to the opposite side. In the case of the crossed pyramidal ract the crossing takes place in the lower part of the medulla obmgata. In the case of the direct pyramidal tract the crossing takes lace in the ventral median fissure of the spinal cord along the course f the tract.

The ground-bundle or intersegmental tracts (fasciculus proprius nterior, Fig. 871, 14; lateralis, Fig. 871, 13; and posterior , Fig. 871, 8) ontain association fibres linking together various parts of the cord, he fasciculus proprius anterior is continued up into the medulla as he posterior longitudinal bundle, but the ground-bundles, as a whole, re regarded as descending tracts.

The vestibulo-spinal tract (fasciculus vestibulo-spinalis, Fig. 871,


1432


A MANUAL OF ANATOMY


ig) is situated in the anterior column, where it lies superficially. It forms a communication between the vestibular structures, through Defiers’ nucleus, with the motor cells of the cord.

The prepyramidal or rubro-spinal tract (Fig. 871, 16) is situated in the lateral column on the ventral aspect of the crossed pyramidal tract. Its fibres are chiefly derived from the red nucleus of the tegmentum or dorsal part of the crus cerebri of the opposite side, and they are regarded as terminating in the dorsal part of the ventral grey matter.

The tecto-spinal tract (fasciculus tecto-spinalis , Fig. 871, 17) runs from the superior corpus quadrigeminum of the opposite side to the motor cells, and lies in front of the rubro-spinal tract.

The bulbo-spinal or olivo-spinal tract, or bundle of Helweg (Fig. 871) 18), is confined to the cervical region of the cord, and is triangular. Its fibres are regarded as arising in the medulla oblongata behind the olive, but their mode of termination is not known. They lie near the surface of the cord external to the anterior nerve-roots.

Ascending Tracts.—The dorsal spino-cerebellar tract, or direct cerebellar tract (of Flechsig) (Fig. 871, 4), is situated in the lateral column. It lies in front of the dorso-lateral sulcus, between the crossed pyramidal tract and the outer surface of the cord.. It commences in the lower part of the thoracic region, and superiorly it traverses the lower part of the medulla oblongata on its lateral aspect, after which it'enters the restiform body, by which it is conducted to the vermis of the cerebellum. Its fibres are usually regarded as being derived from the thoracic nucleus or column of Clarke.

The ventral spino-cerebellar tract, or tract of Gowers (Fig. 871, 5), is situated chiefly in the lateral column, in front of the dorsal cerebellar tract, close to the outer surface of the cord. It is comma-shaped in section, its dorsal part being broad, but as it extends forwards between the funiculi of the ventral nerve-roots it tapers and enters the ventral column superficially. It begins near the lumbar region of the cord. Superiorly it extends through the medulla oblongata and pons, and afterwards passes along the superior cerebellar peduncle into the cerebellum, terminating in the vermis. It therefore takes an indirect course as compared with that of the dorsal spino-cerebellar tract. Its fibres are crossed and are usually regarded as being derived from the thoracic nucleus and posterior horn of the opposite side. The ventral spino-cerebellar tract contains the spino-thalamic and spinotectal tracts.

The spino-thalamic tract (Fig. 871, 6) consists of fibres which arise as the axons of cells of the dorsal grey matter, around which cells the fibres of the dorsal nerve-roots have terminated. The spino-thalamic fibres cross to the opposite side in the ventral or white commissure, thus giving rise to a spinal inferior sensory decussation or spino-thalamic decussation, as distinguished from the superior sensory decussation in the bulb, called the decussation of the fillets, which is produced by the deep arcuate fibres which arise from the cells of the nucleus gracilis and


THE NERVOUS SYSTEM


1433


ucleus cuneatus. The spinothalamic fibres, having crossed in the entral white commissure, ascend in the tract of Gowers, and after raversing the bulb and pons they terminate in the optic thalamus f the side to which they have crossed as a cell-station. It is important d note that there are two sensory decussations —lower or spinal, and pper or bulbar. In unilateral lesions of the spinal cord there would nly be partial anaesthesia on the opposite side; whereas in unilateral

sions of the bulb, involving both the fillet-fibres and the spino-thalamic

bres, there would be complete anaesthesia on the opposite side.

The spino-tectal tract (Fig. 871, 6) is also an ascending tract. Its bres are connected with the cells of the ventral cornu of grey matter, hey ascend in conjunction with the ventral spino-cerebellar tract, and ass through the formatio reticularis of the bulb and pons. After lis they decussate with those of the opposite side, forming the fountain ecussation (of Meynert), which lies between the two red nuclei, to duch nuclei the spino-tectal fibres furnish collaterals. After the ecussation the fibres of either side pass to the corresponding superior illiculus of the corpora quadrigemina.

The tracts of the antero-lateral column may be otherwise arranged s follows:


Ventral Column.

nterior cerebro-spinal tract (descending). (12).

nterior intersegmental (descending)

( 1 4 ) - . ;

ulco-marginal tract (descending)

( 15 ) estibulo-spinal tract (descending)

( T 9);

nterior spino-thalamic tract (ascending) ( 7 ).


Lateral Column.

Lateral cerebro-spinal tract (descending) (11).

Rubro-spinal tract (descending) (16). Tecto-spinal tract (descending) (17). Olivo-spinal tract (descending) (18). Dorsal cerebellar tract (ascending)

( 4 )-.

Anterior spino - cerebellar tract (Gowers, ascending) (5).

Posterior spino-thalamic and spinotectal tracts (ascending) (6). Lateral intersegmental (descending) ( 13 )

The spino-thalamic and spino-tectal tracts (ascending) are contained 1 the ventral spino-cerebellar tract. A part of the postero-lateral isciculus (Lissauer’s tract) lies superficially in the dorsal part of the iteral column, and it has been described in connection with the dorsal olumn.


Association Fibres of Antero-lateral Column—Intersegmental Fasciculi.— The

art of the antero-lateral column which is not occupied by the descending and scending tracts is adjacent to the grey matter, and it constitutes the antero,teral ground-bundle. It is divided into two parts—anterior and lateral.

The anterior intersegmental group is situated in the ventral column in front

the ventral cornu of grey matter, and has been already described.

The lateral group occupies the lateral column ventral and medial to the crossed framidal tract.

The portion of the ventro-lateral ground-bundle adjacent to the grey matter, id almost surrounding it, is known as the limiting zone.

The fibres of the entire antero-lateral ground-bundle are association or ngitudinal commissural fibres, which serve to connect the grey matter of sue


I 434


A MANUAL OF ANATOMY


cessive segments of the spinal cord. They are derived from the cells of the gre matter of the same side, and also of the opposite side, the latter crossing in th ventral or white commissure.

Arteries of the Spinal Canal and Spinal Cord—Arteries of the Spina Canal.—These vessels enter the spinal canal through the intervertebra and sacral foramina. In the cervical region they are branches of th vertebral, deep cervical, and superior intercostal arteries; in th thoracic and lumbar regions they are derived from the dorsal branche of the intercostal lumbar and ilio-lumbar arteries; and in the sacra region they come from the lateral sacral arteries. Within the spina canal each spinal artery divides into three branches—neural or central and anterior and posterior parietal. The neural or central brand pierces the theca of the spinal cord. It supplies the coverings of th cord and the nerve-roots, and it anastomoses with the anterior anc posterior spinal arteries on the cord. This branch is sometimes spokei of as the lateral spinal artery. The parietal branches divide and joii again with one another in such a way that they form five anastomoti( chains in the spinal canal outside the dura mater; of these, one i: antero-median, two antero-lateral, and two postero-lateral.

Arteries of the Spinal Cord.—These are: (i) the anterior spina artery; (2) the posterior spinal arteries, right and left; and (3) th lateral spinal arteries, right and left (neural or central branches jus described in connection with the spinal canal).

The anterior spinal artery is formed by the union of the anterior spinal branches, right and left, of the vertebral arteries. It descend: along the front of the cord in the median line, and is reinforced at regular intervals by the lateral spinal arteries. In this manner ar anterior longitudinal anastomotic chain is formed, which descend: for some distance on the filum terminale.

The anterior spinal branches of the vertebral arteries are seldom of equa size, and often only one is present.

The posterior spinal arteries are two in number, right and left, anc each is a branch of the corresponding vertebral artery. Each vesse descends on the side of the cord in two branches, one being in front of and the other behind the posterior nerve-roots. These are reinforcec by branches from the lateral spinal arteries, and the lateral longitudinal anastomotic chains formed in this manner extend over the entire length of the cord. It will thus be seen that there are five anastomotic chains inside the dura mater in relation to the cord, though they have not quite the same distribution as the extradural; one is antero-median and two on each side postero-lateral. Of these two, one lies in front of and the other behind the posterior nerve-roots.

It is only under very favourable conditions that all these arteries are injected equally.

Veins of the Spinal Column and Spinal Cord—Veins of the Spina) Column.—These veins form two plexuses, extra- and intra-spinal, which for convenience are divided into five groups from behind forward:


THE NERVOUS SYSTEM


1435


) posterior extraspinal, (2) posterior intraspinal, (3) veins of the irtebral bodies, (4) anterior intraspinal, (5) anterior extraspinal.

The dorsal spinous venous plexus is situated deeply upon the supernal surface of the neural arches of the vertebrae under cover of the ultifidus spinae muscle. It receives its tributaries from the integuent and muscles of the back, and it communicates with the posterior ngitudinal intraspinal plexus by branches which pierce the ligamenta iva. In the neck the blood is conveyed away from the plexus by uns which open into the vertebral venous plexus around the vertebral tery of each side; in the thoracic region by veins which join the dorsal ■anches of the intercostal veins; and in the lumbar region by veins hich join the dorsal branches of the lumbar veins.

The veins of the bodies of the vertebrae (venae basis vertebrae) are mtained within the cancellated tissue of the vertebral bodies. They )mmunicate in front with the anterior extraspinal veins, and posteriorly iey terminate in two venous trunks which, emerging through the



Fig. 872. —Schematic Sections to show Positions of Longitudinal

Arterial and Venous Channels.

vo foramina on the posterior surface of each vertebral body, open ito the transverse communicating branch between the two anterior •ngitudinal intraspinal veins.

The anterior longitudinal intraspinal veins form two anastomotic lains, which are situated on the posterior surfaces of the bodies of le vertebrae, one on either side. They communicate with each other pposite the centre of each body by transverse branches which receive le terminal trunks of the venae basis vertebrae. These transverse ranches pass between the posterior longitudinal ligament and the odies of the vertebrae. Superiorly the anterior intraspinal veins )mmunicate with the vertebral and the transverse or basilar plexuses f veins, and laterally an offset passes outwards through each interertebral foramen, which, with that of the posterior intraspinal vein, )rms a plexus around the adjacent spinal nerve.

The posterior longitudinal intraspinal veins are situated in front of le laminae, one on either side, and they are connected at frequent itervals by transverse branches. They communicate with the dorsal




A MANUAL OF ANATOMY


!436

spinous venous plexus by branches which pierce the ligamenta flava. Superiorly they communicate with the marginal sinuses on either side of the foramen magnum and vermiform fossa, which by their union form the occipital sinus. With the marginal sinuses and the anterior intraspinal veins they form a venous ring at the foramen magnum. Laterally each vein sends outwards through the corresponding intervertebral foramen an offset, which, with that of the anterior intraspinal vein, forms a plexus around the adjacent spinal nerve.

The anterior and posterior intraspinal veins are situated between the theca of dura mater and the wall of the spinal canal.

The anterior extraspinal veins form a plexus along the anterior aspect of the bodies of the vertebrae, which is most copious in the neck. On either side it communicates with the vertebral plexus around the vertebral artery in the neck, the intercostal veins in the thoracic region, and the lumbar veins in the lumbar region. It is also connected with the venae basis vertebrae.

Veins of the Spinal Cord.—These vessels lie within the substance of the pia mater, and are disposed as venous chains, one being in front, one behind, and two on either side. The anterior vessel lies over the anterior median fissure beneath the anterior spinal artery; the posterior vessel is also medially placed; and the two lateral vessels are situated one in front of and the other behind the posterior nerve-roots (Fig. 872). Besides these principal chains the veins form a plexus on the surface of the cord. Laterally branches emerge through the intervertebral foramina, which, along with the offsets of the anterior and posterior intraspinal veins, form plexuses around the spinal nerves. From these plexuses the blood is conveyed on either side into the vertebral plexus and deep cervical vein in the neck, and into the intercostal and lumbar veins in the corresponding regions.

Lymphatics.—There are no lymphatic vessels in the spinal cord. Their place is taken by spaces in the outer coat of the arteries, called perivascular spaces, which are in communication with the subarachnoid space.

Development of the Spinal Cord.

The formation of the neural tube from the neural plate and groove is described on pp. 34 and 39. A short general account of the formation of the cord from the tube, and of the spinal nerves, is given on p. 53. Further details are given in the following paragraphs.

The proliferating cells of the early neural tube become confluent and form a syncytium, which is evident in the growing cord to a comparatively late stage. Exhibiting this syncytial character, the ectodermic cells of the wall of the tube undergo proliferation, the wall becomes thickened, and it consists of two kinds of cells—namely, (1) sustentacular or supporting cells, and (2) nervecells proper. The former make the ependyma and neuroglia of the spinal cord, and the latter give rise to the grey and white matter. The loosely arranged syncytial network is known as the myelospongium. This myelospongium becomes condensed internally and externally, and these condensed layers form the internal and external limiting membranes . The wall of the young neural tube is arranged in three layers or zones—namely, (1) inner or ependymal, (2) intermediate or mantle zone, and (3) outer or marginal zone.

The ependymal zone consists of a single layer of elongated cells, connected


THE NERVOUS SYSTEM


1437


th the internal limiting membrane. Their bases are directed towards the nen of the neural tube, and from their apices delicate radial fibres pass outrds to the external limiting membrane. Amongst them there are some concuous cells, called germinal cells. These lie close to the wall of the neural ?e, and by their proliferation they give rise to ependymal cells and neuroblasts, e latter migrate outwards into the mantle zone.

The mantle layer consists mainly of neuroblasts derived from the lining layer ependymal cells, but smaller neuroglial cells are scattered among- these, and ‘ whole is supported by a network of spongioplasm, in which, in fact, the


j. 873.—Three Sections from Different Levels of Cord in Embryo

of 4-9 Mm.

ft lower figure, under higher power, shows nerve-fibres leaving ventro-lateral

wall.

dei may be said to be embedded. Neuroglial fibres develop from the neuroil cells, and extend throughout the thickness of the cord, ramifying and joining Tin the spongy basis.

The marginal zone is the peripheral and outlying part of the spongy netrk, forming a definite layer superficial to the mantle zone. It is a region ich will be occupied by the tracts of nerve-fibres as these form, acting as scaffolding or support for them; it increases enormously in thickness as the r asion by fibres progresses.

As just said, the white matter of the cord is made by nerve-fibres growing


1438


A MANUAL OF ANATOMY


in the marginal zone, the grey matter is formed from the mantle zone, and th ependymal layer, when it has ceased to proliferate and give off the cells of th mantle zone, becomes the lining cell layer of the central canal. The cana itself is the remains of the ventral part of the original cavity of the neural tube

Neuroglial cells have many branches, and are spoken of as glia-cells or spidet cells. The neuroglial fibres are fibrillations of the peripheral protoplasm of th cells, from which they become differentiated.

The neuroblasts lie in groups within the mantle layer, and they give ris to the nerve-cells of the spinal cord. Each cell is primarily unipolar and pear shaped. It has a prominent nucleus, and the body is prolonged into a proces or pole, which represents the axon or axis cylinder process of a nerve-fibre. Sub sequently the pear shape is lost, due to the formation of secondary processes o dendrites, the cell being now multipolar.

Formation of the Cord. —The number of neuroblasts within the mantli zone increases rapidly, the multiplication being due to frequent division of th germinal cells in the ependymal zone.

The division of germinal cells is apparently very extensive and rapid There is doubt, however, as to further addition by division of the nucle within the mantle zone; if there is such division, it is probably amitotic as the occurrence of mitotic figures in this zone is very exceptional.

Whatever may be the origin of all the nuclei, they soon show a tendency t( gather more particularly in dorsal and ventral thickenings on each side. Thu:

there occur longitudinal bulgings on eacl side, showing not only on the oute: surface, but also markedly on the in ternal surface, making the prominence: known as the dorsal (or alar) and ventra (or basal) laminae (Fig. 874) which affeci the form of the contained cavity. Ai interlaminar sulcus runs down the sid( wall of the cavity between these tw( laminae.

A semidiagrammatic sectior across the cord of an embryo ai the end of the first month is given in Fig. 874 to illustrate thes* points. The main collections 0: neuroblasts in the mantle zone make the ventral (V) and dorsa' (D) laminae, separated by the sulcus (IL). A floor-plate, (F) connects the two sides and is composed of a thinner ependymal layer with a fairly thick marginal zone; a roof plate (R) is practically only ependymal. The neural crest, described on p. 53, lies beside the tube on each side, and is represented here by a mass of neuroblasts which will become the posterior root ganglion (G); the interganglionic parts of the neural crest (p. 54) have disappeared by this time, leaving the ganglionic masses in position. Differential disposition of neuroblasts in the mantle zone has begun already.

General Formation. —The neuroblasts of the basal lamina make the cells of the anterior grey column, and the fibres of the afferent roots pass out directly from them. Those of the dorsal lamina are utilized in forming the matter of the posterior grey column. The spinal ganglia send nerve-fibres (posterior roots) into the dorsal region of the cord, the ganglia, as seen, being outside the cord from the beginning. The marginal zone carries fibres from the neuroblasts, and thus increases in depth gradually and continuously; in this way the white matter of the cord is laid down round the grey substance. The cavity, becoming relatively smaller, remains only as the central canal', there is some reason to think


Fig. 874. —Section across Cord, Semi-diagrammatic, about End of First Month.

(Explanation in text.)




THE NERVOUS SYSTEM


J 439


at the dorsal portion of the original cavity is actively obliterated by fusion

tween its walls. The ependymal zone, after its germinal functions have ceased

the end of the second month, becomes the ependymal lining of the canal.

The ventral lamina differentiates ore quickly than the dorsal part, id can be described first. In Fig.

74 it can be seen that a tract of ldei ( b ) is present, having a distinct irso-ventral direction and passing edial to the main ventral or ventroteral neuroblastic mass (a). This tract comes early. Its appearance ggests at first a dorso-ventral igration, but such migration is rtainly not present, and the arngement seems only due to the rection of early fibrils in this tract path, directed towards the floorate, where they cross to the other ie.

This early indication of decussation is of interest. For some fundamental but not very evident reason, the passage of impulses—afferent or efferent —to the opposite side seems to be of basic importance, and a glimpse at the drawings given already will make it clear that the floor-plate is the decussating region; the roof-plate does not seem to provide the necessary marginal zone, and is in fact stretched into a transparent cellular layer higher up, so that the commissural fibres have only the floor-plate for their passage. So far, then, as the primary neural tube extends, all commissural fibres pass ventrally, and the tract b might even be spoken of as a ‘ lateral commissure path ’; such a name, however, would not take account of certain other characters, which might be summed up perhaps in a ‘ path of least resistance,’ so that, for instance, vessels tend to enlarge and lie in this path.

Without labouring the matter further, it will be enough to direct attention to this ' path,’ to which reference will be made from time to time.


Grouping of Ventral Neuroblasts. — Fig. 875 gives tracings from different A els of the cord at 15 mm., showing the modifications found at this period the ventro-lateral group (a of Fig. 874). The groups are not so clearly marked, course, as indicated in the tracings, but are nevertheless quite evident; uC d mC are upper and middle cervical levels, uD and mD are upper and middle












1440


A MANUAL OF ANATOMY


thoracic, and iL and mL are first and middle lumbar levels. The ‘ commissun path ’ already mentioned is shown at b, and the grouping of neuroblasts seems i correspond well with the condition in the adult cord; hence the arrangements i the ventral grey column appear to be attained at an early stage. The group c, i the cervical and upper thoracic sections, increases in size as it is traced upward; It is composed of neuroblasts originating from the ependymal zone at the sam level of origin as. the a group, but separated from this last collection by the pat b ; this suggests that it might be looked on as of the same morphological value a the a group, but of later development. Whether this way of regarding it i justifiable or not, the group is responsible for supplying the hypoglossal nucleu and (possibly) that of the sixth nerve, while the a group, at the hypoglossal leve is apparently taken into the formation of the olive; this will be dealt with in th proper place.

Dorsal Lamina and Associated Formations. —The neuroblasts of the dorsa lamina increase and differentiate slowly, forming a massive but apparent! undifferentiated collection in the second month, when the ventral formation (Fig. 875) are evident. There is at first very little marginal zone over thi dorsal collection, but about the end of the first month the fibrils growing ii from the ganglionic mass, beside the cord, begin to collect as a small bundl (C, Fig. 874) on the dorso-lateral aspect of the neuroblastic mass. This bund! is the earliest sign of the posterior white column, and increases rapidly in size, a the same time extending medially. The bundle is to be identified with thi cuneate fasciculus. The medial extension no doubt helps to form the gracil fasciculus, but this may have some separate formation as well. The postero lateral tract (Lissauer’s zone) begins to form a little later, as the entering fibre; of the posterior root increase in number.

The method of elongation of the posterior horn is not clear; doubtless th< increasing depth of the surrounding white columns has something to do with it but the other factors are not apparent.

The deposition of fibrils within the marginal zone to make the white column! goes on, seemingly, throughout foetal life; they can be recognized in the firs' part of the second month at least, and perhaps earlier than this. It may b( assumed that the shorter fibres are formed first, and occupy the marginal zon< close to the neuroblasts; thus we get the short intersegmental fibres clothing the grey matter. The subsequently developed longer fibres are laid down or these short ones, and the latest developed would be the most superficial; thu; we find long fibres reaching the mid-brain and thalamus, and superficial to these although mixed with them to some extent, fibres running to the cerebellum, a later formation. This, in a general way, agrees with what is known about the position of such tracts in the cord.

The downward-running tracts doubtless follow a comparable regulation ir their disposal, but the matter of decussation is important here. The cerebrospinal fibres, for example, decussate for the most part immediately before entering the cord, and thus pass at once into the b path mentioned above; following this, they reach the space ventral to the posterior horn and Lissauer’s tract, in which they lie as the lateral cerebro-spinal or crossed pyramidal tract. The uncrossed fibres ultimately cross and also enter the b path, from which they reach the anterior horn.

Myelinization. —The tracts are at first made up of axis cylinders alone, and these acquire myelin sheaths subsequently. The time when this occurs differs in the various tracts. The process begins about the fourth or fifth month in the root fibres, and after this appears in the tracts more or less in the order of their formation as laid down above. The pyramidal fibres do not begin to develop their sheaths till about the time of birth, and the process is said to continue until after puberty.

Caudal End of Spinal Cord. —This undergoes certain modifications. It can be seen in Fig. 877 that a tail process, bent dorsally, represents the atrophied remnant, in the early part of the second month, of the large ‘ tail ’ of younger stages. This tail process contains a prolongation from the neural tube; it


THE NERVOUS SYSTEM


1441

smains up to about the 18 mm. stage, when the atrophied filament vanishes, arrying with it the included neural prolongation. Fig. 876 shows two median mgitudinal sections of the end of the cord in embryos of 16 and 35 mm. repectively, the tail remnant being present in the younger specimen, although rst about to disappear. The neural cell-layers in this remnant are continued ito a canal (c), the walls of which are continuous with the ependymal layers f the cord. A second canal (vc) is seen on its ventral side, the cavity of which pens into the central cavity of the cord (the continuity is not very clear in ledian section). The central cavity of the cord ends in a dilated ventricle, diich seems to be a normal condition at this stage. That part of the neural ibe which corresponds with the quondam tail is evidently disappearing, shows regular growth, and is represented by remnants.

In the 35 mm. embryo the tail has gone, and the caudal neural remnant shows coccygeal vestigial cyst {cyst) where the caudal portion has separated, the


toirqinal jone / (ye rtf. comm.)


16 mm


!f- -\coccyK

cyst/ v


Fig. 876. —Median Sagittal Sections of Ends of Cords in Sixth and

Ninth Weeks.

Ependymal tissue shown in black. Description in text.


yrst lying very near the surface. Some nerve-fibres have developed in connection ith this {%/) and pass to the cord itself. Remnants of this canal are seen irther forward, and the ventral canal is seen opening into the ventral part of

le terminal ventricle, as in the younger stage.

After this stage the cord does not grow in length at the same rate as the ertebral column, so that its caudal end gets farther and farther away from the Dccygeal region. Hence, the vestigial cyst remaining in situ with a superficial ttachment, the intervening cell-strands are drawn out in a lengthening conection The main cell masses caudal to the ventricle are drawn up with it, taking the nervous elements found in the upper end of the filum terminate; le rest of the filum is composed of drawn-out pia mater, the included and

fetched nerve-tissue having disappeared.

The coccygeal vestigial cyst enlarges somewhat and develops nerve-tissue )und it, but disappears during the later foetal months; it is a possible cause, y persistence, of certain congenital cysts found near the coccyx.


9i



1442


A MANUAL OF ANATOMY


Membranes of Spinal Cord. —The membranes—namely, pia mater, arachnoid and dura mater (theca)—are developed from the mesoderm which invests th neural tube.

Growth of Spinal Cord. —The cord originally occupies the entire length o the spinal canal of the vertebral column. The vertebral column, however grows more rapidly than the cord, so that at the period of birth the cord does no extend lower than the level of the third or fourth lumbar vertebra. Sub sequently its lower limit is the intervertebral disc between the bodies of th first and second lumbar vertebrae. This produces a change in the course o the lumbar, sacral, and coccygeal nerves. In order to reach the level of th intervertebral foramina through which they emerge from the spinal cana they descend almost vertically, and constitute the bundles of nerves known a the cauda equina.

A linear reconstruction of the coccygeal portion of the cord in a 15 mm embryo is given in Fig. 877. It shows the atrophying tail-remnant, with it included piece of neural tissue, but also shows, proximal to this, a portion o nerve-tube truly coccygeal in nature and position, from which take origii four (? or more) nerves behind the coccygeal nerve. These post-coccygea nerves, which have double roots, join with each other and with the coccygea


Fig. 877. —Linear Reconstruction of Caudal End (15 Mm.), showing thi Prolongation of Cord into the Tail Filament, and the Presenci of Four Nerves beyond the Coccygeal.

The vertebral levels of the spinal nerves are indicated.

nerve in a series of ill-defined loops. They emerge between the rudimentar] vertebrae caudal to the sacrum. The broken-up post-coccygeal portion of th( cord is in part carried up with the persisting coccygeal portion, and in pari left behind; the intermediate part is drawn out with the filum terminale. Som< nervous matter still persists at the upper end of this structure. The post coccygeal nerves atrophy and disappear, but Rauber has described remains of ganglia and nerves beside the upper part of the filum, which may repre sent remnants of the upper post-coccygeal nerves, drawn up with the cord.


THE ENCEPHALON.


The encephalon is the part of the cerebro-spinal axis which if contained within the cranial cavity. It is composed of the medulh oblongata, pons Varolii, cerebellum, and cerebrum. In the embryc it consists of three hollow vesicles.


Encephalon =

Prosencephalon or Fore-brain. Mesencephalon or Mid-brain. Rhombencephalon or Hind-brain.



THE NERVOUS SYSTEM


1443


The subdivisions of the prosencephalon are the telencephalon and he thalamencephalon or diencephalon; the mesencephalon remains mdivided; and the subdivisions of the rhombencephalon are the metncephalon and the myelencephalon.


Fore-brain or Prosencephalon = { ^alamencephalon or Diencephalon. Mid-brain or Mesencephalon = Mesencephalon.

Hind-brain or Rhombencephalon = { Mydenceplulon.


rhe various parts of the encephalon which are developed from these ubdivisions will be made evident from the following table:


Telencephalon


Thalamencephalon

or

Diencephalon

Mesencephalon

Metencephalon

Myelencephalon



Cerebral Hemispheres.

Lateral Ventricles.

Anterior Part of Third Ventricle. Interventricular Foramina.

Olfactory Lobes.

Posterior Part of Third Ventricle.

Optic Thalami and Corpora Geniculata. Pineal Body.

Interpeduncular Structures.

Pituitary Body.

Optic Nerve and Retina.

Corpora Quadrigemina.

Crura Cerebri.

Aqueduct (of Sylvius).

Cerebellum.

Pons (Varolii).

Pontine Part of the Fourth Ventricle.


( Medulla Oblongata (or Bulb).

\ Bulbar Part of Fourth Ventricle.


General Description of the Base and Superior Surface of the

Encephalon.

The inferior aspect of the encephalon is known as the base. In the allowing general description of the parts which it presents the order pursued is, as nearly as possible, from behind forwards and upwards.

The medulla oblongata (or bulb) lies on the under aspect of the

erebellum in the median line, occupying the vallecula which separates

the two cerebellar hemispheres. The surface exposed is the ventral surface, which presents (1) the anterior median sulcus, crossed at its tower part by the decussation of the pyramids; (2) the pyramid, on sither side of this sulcus; and (3) the olivary body, external to each pyramid.

The hemispheres of the cerebellum lie one on either side of the medulla oblongata, and they conceal from view the posterior parts of the cerebral hemispheres and the posterior part of the great longitudinal fissure. They are characterized by the laminated arrangement of their nervous matter, the laminae being curved and separated from



1444


A MANUAL OF ANATOMY


each other by fissures. Posteriorly the hemispheres are separated fror each other by the posterior notch. When the medulla oblongata i raised, and the cerebellar hemispheres slightly separated from each othei the vallecula is fully exposed, and the inferior vermis is seen lyini deeply in it, with the sulcus vallecula on either side of it.

The pons' (pons Varolii) forms a prominent elevation above th medulla oblongata, the surface exposed being the ventral surface. L the median line this surface presents a longitudinal groove, which i


Olfactory Bulb Olfactory Tract


Lateral Sulcus


Optic Nerve


Gyrus Rectus


Subst. Perfor Ant.


Tuber Cinere and Infundibi Corpus Mami


Crus Cerebri


Area Perforal Post.


Fifth Nerve Sixth Nerve

Facial Nerve Pars Intermedia


Auditory Nerve-' Glossopharyngeal Nerve Vagus Nerve

Accessory Nerve


Oblongata


Hypoglossal Nerve


Fig. 878. —The Base of the Encephalon, and the Cranial Nerves. 1, frontal lobe (orbital surface); 2, temporal lobe; 3, cerebellum.


occupied by the basilar artery. On either side the pons becomes th<

middle peduncle of the cerebellum, passing outwards and backwards into the cerebellar hemisphere.

The temporal lobes of the cerebrum are situated in front of the cerebellar hemispheres, and are conspicuous by their prominence. Each terminates anteriorly in a projecting extremity, called the

temporal pole.

The stem of the lateral sulcus lies immediately in front of the













THE NERVOUS SYSTEM


1445


mporal lobe, and is occupied by the middle cerebral artery. At the

iner end of the stem of the fissure is the depression often referred to 5 the vallecula Sylvii or vallecula cerebri.

The frontal lobes of the cerebrum lie in front of the stem of the ,teral fissure. The exposed parts are the orbital surfaces, each of hich is separated from its fellow of the opposite side by the great ingitudinal fissure. Each orbital surface presents a straight fissure, died the olfactory sulcus, which is situated near the great longitudinal ssure, and is parallel to it. This sulcus is occupied by the olfactory •act and olfactory bulb.

The crura cerebri, or peduncles, right and left, appear at the upper order of the pons, and soon diverge from each other as they pass awards and upwards to sink into the cerebral hemispheres.

The optic tract of each side winds round the outer and ventral spects of the corresponding crus cerebri. Its course is forwards and lwards towards its fellow of the opposite side.

The optic commissure, or chiasma, connects the two optic tracts fter their convergence.

The optic nerves, right and left, leave the front of the commissure, nd pass forwards and outwards to the optic foramina.

The interpeduncular space is situated in front of and above the ons. It is somewhat diamond-shaped, and its boundaries are as dlows: posteriorly, the divergence of the crura at the upper border f the pons; anteriorly, the optic commissure; and, laterally, the crus erebri and optic tract from behind forwards. The following parts e within this space, in the order named, from behind forwards: (1) the rea perforata posterior; (2) the corpora albicantia or mamillaria; nd (3) the tuber cinereum, with the infundibulum. The structures ccupying the interpeduncular space form for the most part the floor f the third ventricle.

The area perforata posterior or posterior perforated substance

Drresponds to the posterior median angle of the diamond-shaped intereduncular space, and it lies in a deep depression, called the intereduncular fossa (or fossa Tarini). The grey matter which forms it is erforated by openings for the passage of the postero-medial branches f the posterior cerebral arteries.

The corpora mamillaria are situated directly in front of the area erforata posterior, and present the appearance of small, white, peake bodies lying close to the median line.

The tuber cinereum extends from the mammillary bodies to the ptic commissure, and is composed of grey matter. The infundibulum

connected with the tuber cinereum close behind the optic comlissure, and passes downwards to the posterior part of the pituitary

ody.

The area perforata anterior or anterior perforated substance of each de coincides with the vallecula at the inner end of the stem of the iteral fissure. It lies outside the interpeduncular space, close to the uter aspect of the optic commissure. It consists of grey matter, which


I446


A MANUAL OF ANATOMY


is perforated by openings for the passage of a few antero-medial branches of the anterior cerebral artery, and numerous antero-lateral branches of the middle cerebral artery. These branches are destined for the nucleus caudatus and nucleus lenticularis of the corpus striatum, the grey matter of which nuclei comes to the surface of the brain at the anterior perforated substance.

The medulla oblongata and pons occupy the basilar groove of the interior of the base of the skull; the cerebellar hemispheres occupy the cerebellar fossae of the occipital bone; the temporal lobes of the cerebrum sink deeply into the lateral divisions of the middle fossa of the base of the skull; the orbital surfaces of the frontal lobes occupy the lateral divisions of the anterior fossa; the stem of the lateral fissure faces the posterior border of the small wing of the sphenoid; the optic commissure lies above the olivary eminence and optic groove of the sphenoid; and the olfactory bulb rests upon one half of the cribriform plate of the ethmoid bone. The olfactory bulb and olfactory tract, essential parts of the brain, occupy the olfactory sulcus on the orbital surface of the frontal lobe near the great longitudinal fissure; and the olfactory filaments pass through the foramina of the cribriform plate of the ethmoid bone on their way from the olfactory cells of the olfactory mucous membrane to the olfactory bulb. Posteriorly the olfactory tract divides into two roots, medial and lateral. The medial root curves inwards behind the ‘ area of Broca ’ to the callosal gyrus. The lateral root passes backwards and laterally across the outer part of the area perforata anterior. The triangular area of grey matter, which is situated between the diverging roots of the olfactory tract, is called the trigonum olfactorium. It is sometimes spoken of as the middle or grey root of the olfactory tract. The area of Broca is situated in front of the medial (inner) root of the olfactory tract, and is continuous with the callosal gyrus.

Superficial Origins of the Cranial Nerves.

The first or olfactory nerve is represented by the filaments which, as has been seen already, have their superficial origin from the lower surfaces of the olfactory bulbs and pass through the cribriform plate.

The second or optic nerve is connected with the lateral extremity of the front part of the optic commissure.

The third or oculo-motor nerve emerges through the oculo-motor sulcus on the inner aspect of the crus cerebri, just above or in front of the pons, and close to the posterior perforated substance.

The fourth or trochlear nerve, having emerged from the upper part of the superior medullary velum, makes its appearance in the interval between the crus cerebri internally and the temporal lobe externally.

The fifth or trigeminal nerve consists of two roots, which emerge close together from the lateral aspect of the ventral surface of the pons. The sensory root is large, and the motor root, which is small, lies above and slightly medial to the sensory root.


THE NERVOUS SYSTEM


1447


The sixth or abducent nerve appears at the lower border of the pons ust lateral to the pyramid of the medulla oblongata.

The seventh or facial nerve emerges at the lower border of the pons n front of the restiform body of the medulla oblongata.

The eighth or auditory nerve likewise appears at the lower border of

he pons in front of the restiform body of the medulla oblongata,

[t lies on the outer side of the facial nerve.

The N. intermedins is a small nerve which appears between the facial md auditory nerves. It is regarded as the sensory root of the facial lerve.

The ninth or glosso-pharyngeal nerve emerges, in the form of about fix fasciculi, from the postero-lateral sulcus of the medulla oblongata, Detween the olivary body and the restiform body, immediately below the facial nerve.

The tenth or vagus nerve lies directly below the glosso-pharyngeal nerve, and emerges by several fasciculi from the postero-lateral sulcus Df the medulla oblongata in front of the restiform body.

The eleventh or accessory nerve has several roots which lie below the fasciculi of the vagus nerve. These rise (a) from the medulla nblongata and ( b ) the upper part of the lateral column of the spinal

ord as low as the level of the fifth cervical nerve. The first is the

zranial origin of the nerve, the second its spinal root. They lie below the fasciculi of the vagus nerve, and external to, or in front of, the posterior roots of the adjacent cervical spinal nerves.

The twelfth or hypoglossal nerve emerges by several fasciculi through the antero-lateral sulcus of the medulla oblongata between the pyramid and the olivary body. These fasciculi lie in line with the sixth nerve superiorly.

Arteries at the Base of the Encephalon. —The arteries which supply the brain are the two vertebral and the two internal carotid arteries.

The vertebral arteries incline medially as they ascend on the ventral aspect of the medulla oblongata, and at the lower border of the pons they unite to form the basilar artery. The branches of each vertebral artery to be noted are as follows: (1) the posterior spinal branch , which arises from the main vessel immediately after it has pierced the dura mater, and descends upon the side of the medulla oblongata to the spinal cord; (2) the anterior spinal branch , which arises higher up than the preceding, and passes downwards and inwards on the ventral aspect of the medulla oblongata to unite with its fellow and form the anterior spinal artery ; and (3) the posterior inferior cerebellar branch, of large size, which arises from the main vessel near the pons, and passes backwards round the medulla oblongata to enter the vallecula of the cerebellum.

The basilar artery extends from the lower border of the pons to the upper border, occupying the basilar groove on its ventral surface. It is formed by the union of the two vertebral arteries, and terminates by dividing into the two posterior cerebral arteries. The branches of the basilar artery to be noted on either side are as follows. (1) the


1448 A MANUAL OF ANATOMY

transverse arteries of the pons ; (2) the internal auditory artery , which accompanies the auditory nerve through the meatus auditorius internus; (3) the anterior inferior cerebellar artery , which arises from the basilar about its centre, and passes backwards to the inferior surface of the cerebellar hemisphere; (4) the superior cerebellar artery , which arises from the basilar near its termination, and passes laterally close to the


upper border of the pons, and then round the outer side of the crus cerebri to the superior surface of the cerebellar hemisphere; and (5) the posterior cerebral artery , which arises from the termination of the basilar, and passes laterally parallel to the superior cerebellar artery, and then round the crus cerebri to the inferior surface of the occipital lobe. The posterior cerebral and superior cerebellar arteries are separated from


}




THE NERVOUS SYSTEM


1449


iach other by the third and fourth cranial nerves. The branches of

he posterior cerebral artery are
(1) postero-medial, which pass to the

posterior perforated substance; (2) postero-lateral, which pass round

he crus cerebri; and (3) posterior choroidal, which pass to the upper

Dart of the choroidal fissure.

The internal carotid artery of each side appears at the vallecula

erebri, and there divides into the anterior and middle cerebral arteries.

Near its termination it gives off the posterior communicating artery, which passes backwards to join the posterior cerebral artery. It also pves off the anterior choroidal artery, which passes backwards and Dutwards between the crus cerebri and the uncinate gyrus to the lower and anterior part of the choroidal fissure.

The anterior cerebral artery passes forwards and inwards between the optic nerve and the medial root of the olfactory tract, and enters the great longitudinal fissure.

As it is about to enter that fissure it is connected with its fellow of the opposite side by the anterior communicating artery, which is short, but of fairly large size.

Amongst other branches the following are to be noted arising from the anterior cerebral artery: (1) anteromedial, few and inconstant; and (2) antero-lateral, both of which pass to the anterior perforated substance.

The middle cerebral artery, of large size, sinks into the lateral fissure, which it traverses in an outward ‘direction. Before disappearing into the fissure antero-lateral ganglionic branches are to be noted arising from it, which are arranged in two sets, medial and lateral striate, for the corpus striatum and internal capsule.

Circulus Arteriosus.—This is an important communication between the vertebral and internal carotid arterial systems at the base of the brain, which is situated around the interpeduncular space. It is not actually a circle, though so named, but is a heptagon—that is to say, it has seven angles and seven sides.

Beginning at the median line posteriorly, and proceeding forwards on either side to the median line in front, at the great longitudinal fissure, the component arteries of the circle are: (1) the basilar, (2) the posterior cerebral, (3) the posterior communicating, (4) the internal

arotid, (5) the anterior cerebral, and (6) the anterior communicating.

These communications serve to insure a uniform supply of arterial fiood to the brain in cases of obstruction to one or other of the principal irterial trunks. The communications also serve to equalize the circu

1. Internal Carotid

2. Middle Cerebral

3. Anterior Cerebral

4. Anterior Communicating

5. Posterior Communicating

6 . Posterior Cerebral

7. Basilar

8 . Superior Cerebellar

9. Transverse Pontine xo. Internal Auditory xr. Anterior Inferior Cerebellar

12. Posterior Inferior Cerebellar

13. Vertebral

14. Anterior Spinal

15. Posterior Spinal

16. Anterior Choroid

17. Posterior Choroid

18. Cential or Ganglionic

19. Central or Ganglionic

20. Central or Ganglionic (Postero-mesial)

‘21. Central or Ganglionic (Postero-lateral)

Fig. 880. —The Arteries at the Base of the Brain, and the Circulus Arteriosus.


13 15 14



1450


A MANUAL OF ANATOMY


lation of blood through the different parts of the brain, an arrangement which, though doubtless advantageous, cannot be essential, since one or both of the posterior communicating arteries are often very small and sometimes absent.

Superior Surface of the Brain. —The brain is ovoid superiorly, its greatest breadth corresponding to the positions of the parietal eminences of the parietal bones. In the median line it presents a deep cleft, called the longitudinal fissure, which extends from the front to the


Great Longitudinal Fissjarc


Fig. 88i.—The Cerebral Hemispheres (Superior View). Fissure of Rolando—central fissure.


back, and divides it into two hemispheres, right and left. This fissure is occupied by a process of the dura mater, called the falx cerebri, and the corpus callosum lies at its deep part. In front of the corpus callosum the fissure extends down to, and is visible on, the base of the brain, but behind the corpus callosum it only extends to the level of the tentorium cerebelli, which separates the cerebellum from the posterior parts of the cerebral hemispheres. The fissure, therefore, in this situation is not visible inferiorly until the cerebellum and the tentorium cerebelli have been removed.


/



THE NERVOUS SYSTEM


1451


Each hemisphere is semi-ovoid, its medial surface being flat. The anterior and posterior extremities are rounded, the former being the thicker of the two. The anterior extremity is known as the frontal pole, and the posterior extremity forms the occipital pole. The surface of each hemisphere consists of grey matter, which is spoken of as the cerebral cortex. Superiorly and externally it is convex in adaptation to the concavity of the vault of the cranium. It is broken up into a number of tortuous eminences, called gyri or convolutions, and these are separated from each other by clefts, called sulci or fissures. The surfaces of the gyri which bound the sulci are covered with grey matter, like their exterior. The pia mater closely covers the gyri, and also dips into the sulci, so as to cover the opposed surfaces of the gyri. The arachnoid membrane, however, does not dip into the sulci, but passes over them. The sulci are of various depths, but the average depth is about J inch.

RHOMBENCEPHALON.

1. The Medulla Oblongata.

The medulla oblongata (or bulb) is continuous with the spinal cord, and extends from the lower margin of the foramen magnum of the occipital bone to the lower border of the pons. Its direction is upwards and forwards, and it measures 1 inch in length, f inch in breadth at the widest part, and fully \ inch in thickness. Interiorly its girth corresponds with that of the spinal cord, but it widens superiorly, so that it is somewhat pyramidal. Its ventral surface faces the basilar groove of the occipital bone, and its dorsal surface is directed towards the vallecula of the cerebellum.

The bulb is composed of two symmetrical halves, its bilateral symmetry being indicated superficially by upward prolongations of the ventral or anterior sulcus and dorsal or posterior median septum of the spinal cord. The anterior median fissure extends as high as the lower border of the pons, where it expands slightly and forms a blind recess, called the foramen ccecum. In its lower part this fissure is interrupted and crossed by bundles of nerve-fibres, which are derived from the inner three-fourths of each pyramid, the decussation thus formed being known as the decussation of the pyramids, or motor decussation. The posterior median septum only extends along the lower half of the bulb, and it terminates superiorly at the point of divergence of the margins of the fourth ventricle.

Each half of the bulb presents two grooves. The antero-lateral sulcus is situated between the pyramid and the olivary body, and along this sulcus the roots of the hypoglossal nerve emerge in line with the ventral roots of the spinal nerves. Whilst, however, the latter are spread over a certain area, the hypoglossal roots emerge along a straight line corresponding to the ventro-lateral sulcus of the bulb. This sulcus is not represented on the surface of the spinal cord. The posterolateral sulcus lies on the dorso-lateral aspect of the olivary body. Along


1452


A MANUAL OF ANATOMY


this sulcus, in order from above downwards, there are (i) the roots of the glosso-pharyngeal nerve, (2) the funiculi of the vagus nerve, and (3) the funiculi of the bulbar part of the accessory nerve.

The bulb in its lower half contains a prolongation of the central canal of the spinal cord. This part of the bulb is spoken of as the closed part , and it extends as high as the level of the lower point of the ventricle. In the upper half of the bulb the central canal opens out at this level into the ^fourth ventricle, and the dorsal aspect of the bulb forms the lower,.or bulbar half of the floor of the fourth ventricle. The upper half of. the bulb is therefore spoken of as the open part.


Optic Commissure

Optic Nerve

Infundibulum, - ~

Tuber Cinereum '■» * # „ . „

C Optic Tract

Mamillary Body . /

Third Nerve

Mesial Root of Optic Tract '

Lateral Root of Optic Tract Lateral Geniculate Body


Post.Perforated Subst.


Fourth Nerve


Sixth Nerve


Root of Fifth Nerve Root of Fifth Nerve


Facial Nerve

Pars Intermedia Auditory Nerve - Glosso-pharyngeal Nerve -Vagus Nerve Superficial Arcuate Fibres—

Accessory Nerve-"

First and Second Cervical Nerves;^


Middle Peduncle of Cerebellum

Inferior Peduncle - — Hypoglossal Nerve ..Anterior Median Fissure

Decussation of the Pyramids


Fig. 882. —The Medulla Oblongata, Pons, and Interpeduncular Region. C.C., crus cerebri; P., pyramid; O.B., olivary body.


The surface of each half of the bulb is divided into three areas by the above-mentioned sulci, with the corresponding nerve funiculi. These surface areas are ventral, lateral, and dorsal.

Ventral or Anterior Area.—This superficial area is situated between the median and the antero-lateral sulcus, along which the funiculi of the hypoglossal nerve emerge. It constitutes the pyramid of the bulb. The two pyramids, right and left, represent the motor tracts of the bulb. As regards position, the pyramid is like the anterior column of the spinal cord, and it consists of bundles of nerve-fibres disposed longitudinally. Inferiorly it is somewhat narrow, but it widens superiorly. At the lower border of the pons it undergoes a slight constriction, after which it sinks into the pons. As it traverses the pons its funiculi become separated into several strata, and these are gathered together at the upper border of the pons into the crus cerebri of the corresponding side.





THE NERVOUS SYSTEM


1453


Inferiorly each pyramid is disposed in two parts—medial and lateral. The medial portion represents as a rule the inner three-fourths, and its fibres cross to the opposite side in the lower part of the ventral median sulcus of the bulb. Thereafter they sink deeply into the dorsal part of the lateral column of the spinal cord on the side to which they have crossed, where they constitute the crossed pyramidal or lateral cerebro-spinal tract. The intercrossing of fibres which takes place in the lower part of the ventral median fissure of the bulb is called the decussation of the pyramids, or the motor decussation, and, as stated, it usually involves the fibres of the inner three-fourths of the pyramid.

The lateral portion of the pyramid represents as a rule the lateral fourth, and its fibres take no part in the decussation. The path of most of them is downwards into the anterior column of the spinal cord of the same side, where they lie close to the anterior median fissure of the cord and constitute the direct pyramidal or anterior cerebro-spinal tract. A few of them, however, descend into the lateral column of the same side, and constitute the uncrossed lateral pyramidal tract.

The pyramid of the bulb, therefore, only corresponds topographically with the anterior column of the spinal cord. The direct cerebro-spinal tract of the anterior column of the cord forms the greater part of the lateral fourth of the corresponding pyramid of the bulb; and the crossed cerebro-spinal tract of the lateral column of the cord forms the medial three-fourths of the pyramid of the opposite side. The remainder of the anterior column of the cord sinks deeply into the bulb and lies on the dorsal aspect of the pyramid.

The ventral surface of each pyramid is crossed above the level of the decussation of the pyramids by the anterior superficial arcuate fibres , which emerge from the ventral median fissure and take an arched course outwards and then backwards to the inferior cerebellar peduncle.

The sixth cranial nerve emerges close to the lower border of the pons, immediately lateral to the pyramid, and in line with the funiculi of the hypoglossal nerve as these leave the ventro-lateral sulcus.

Lateral Area of the Medulla Oblongata.— This superficial area is situated behind the funiculi of the hypoglossal nerve. Superiorly the oval eminence, called the olive, is included in it. Inferiorly it has the appearance of being a prolongation of the lateral column of the spinal cord, but this is not the case. The crossed cerebro-spinal tract of the lateral column of the cord sweeps obliquely across to the opposite side, where it forms the greater part of the pyramid of that side. The parts, therefore, of the lateral column of the cord which form the lateral area of the bulb below the olive are (1) the dorsal or direct spinocerebellar tract, (2) the ventral spino-cerebellar tract, and (3) the lateral intersegmental bundle. The dorsal spino-cerebellar tract, as it ascends, soon inclines obliquely backwards to join the inferior peduncle. The ventral spino-cerebellar tract and intersegmental bundle ascend until they reach the lower end of the olive. They then in part sink deeply, and ascend to the pons on the dorsal or deep aspect of the olive. Most


T 454


A MANUAL OF ANATOMY


of the cerebellar fibres, however, remain on the surface, and ascend in the small interval which lies between the outer part of the olive and the funiculi of the glosso-pharyngeal and vagus nerves.


Fig. 883.—A Sketch to show the Disposition of Spinocerebellar Fibres in Lateral Region of Medulla.


The lateral area of the bulb below the olive thus represents the dorsal or direct spino-cerebellar tract, ventral spino-cerebellar tract, and, deeply, the lateral ground-bundle of the lateral column of the spinal cord of the same side (Fig. 883).

Superiorly, as stated, the lateral area presents an oval eminence, called the olive. It lies between the funiculi of the hypoglossal nerve on the one hand, and the funiculi of the glosso-pharyngeal and vagus nerves on the other, with the intervention of some ascending fibres belonging to the ventral spino-cerebellar tract. Its long axis is placed vertically, and in this direction it measures about J inch. Superiorly it is separated from the pons by a deep transverse groove, and interiorly the anterior superficial arcuate fibres arch over its lower part.

At the lower border of the pons, lateral to the upper end of the olive, the facial and auditory nerves make their appearance. The facial nerve is in line


The dorsal fibres (interrupted lines) run to inferior peduncle, therefore have a dorsal tendency as they ascend, covering in the spinal root of fifth nerve, which is making a slight prominence, the tuberculum gelatinosum (T). The ventral fibres (Gowers’ tract) are dotted. The arrows indicate many fibres from other parts (olives, etc.), helping to complete the peduncle. C, G, cuneate and gracile tubercles ; P.R.O., position of pallidorubro-olivarv tract.


closed and open part of the lower and upper.


with the roots of the glosso-pharyngeal nerve. The auditory nerve appears lateral to the facial nerve, and between the two is the small pars intermedia (of Wrisberg ).

Dorsal or Posterior Area of the Medulla Oblongata.—This superficial area is limited in front by the sulcus containing the funiculi of the glosso-pharyngeal, vagus, and bulbar part of the spinal accessory nerves. Posteriorly its lower half extends as far as the dorsal median fissure, and its upper half extends only as far as the lateral boundary of the lower or bulbar half of the floor of the fourth ventricle. Inasmuch as this area belongs to both the bulb, it will be considered in two sections—


Lower Portion of Posterior Area. —This, it has been shown, is limited behind by the dorsal median fissure, and it is in direct continuity with the dorsal column of the spinal cord of the same side, which is composed






THE NERVOUS SYSTEM


  • 455


>f the gracile and cuneate columns. It presents three longitudinal minences—namely, the funiculus gracilis, funiculus cuneatus, and uniculus gelatinosus.

The funiculus gracilis is a prolongation of the column of the spinal ord, and lies close to the dorsal median fissure. The funiculus cuneatus 3 a prolongation of the column of the cord, and lies lateral to the uniculus gracilis, from which it is separated by an upward continuation >f the dorsal intermediate or paramedian furrow of the cord.

At the lower level of the ventricle each of these two funiculi )ecomes enlarged and terminates in a prominence or bulb. The enargement formed by the funiculus

racilis is called the clava, or gracile

ubercle, and that formed by the funi:ulus cuneatus is termed the cuneate ubercle. The two clavae, right and left, ie on either side of the lower angle of he fourth ventricle, and as the bulb >pens out dorsally at this level to form he lower or bulbar half of the floor of he fourth ventricle each clava is dis)laced laterally. An angular interval low separates the two clavae, and the irolongation of the central canal of the pinal cord through the lower or closed >art of the bulb opens into the fourth ventricle in the angle between the two

lavae.

The funiculus gracilis, with its tu>ercle, and the funiculus cuneatus, with ts cuneate tubercle, are to a large exent produced by the collections of grey natter which they contain—namely, the mcleus gracilis and nucleus cuneatus.

The funiculus gelatinosus is situated >n the outer side of the funiculus cuneatus, between it and the funi:uli of the bulbar part of the spinal accessory nerve. It is produced >y the substantia gelatinosa (of the spinal cord), which is close to the urface in the lower or closed part of the bulb. Interiorly the funiculus s narrow, but it widens as it ascends, and superiorly it terminates n an enlarged extremity, called the spinal tract of the trigeminal or uberculum gelatinosum.

The funiculus and tubercle are covered by a thin layer of longiudinal nerve-fibres which represent the spinal or descending sensory oot of the fifth cranial nerve.

Upper Portion of Posterior Area.— This belongs to the upper or open >art of the bulb, and extends as far as the lateral boundary of the ower or bulbar half of the floor of the fourth ventricle. It presents l prominent round tract, called the restiforrn body , which is situated


Fig. 884.—Posterior View of Medulla.

G, C, gracile and cuneate tubercles ; g, c, corresponding tracts; F, gelatinous tubercle; O, obex.







A MANUAL OF ANATOMY


1456

between the lower half of the floor of the fourth ventricle and the funiculi of the vagus and glosso-pharyngeal nerves. Its direction is upwards, outwards, and backwards, and it enters the corresponding hemisphere of the cerebellum. It is otherwise known as the

inferior cerebellar peduncle.

The inferior peduncle succeeds to the funiculus gracilis and funiculus cuneatus of the lower portion of the posterior area of the bulb, but it is quite distinct from these funiculi, and receives no fibres from them. The sources of its fibres will be given in connection with the internal structure of the bulb (see p. 1463). Meanwhile, it is


Fig. 885.—Section through Medulla just above Decussation of Pyramids: Shows the Prominence of Spinal Tract of Fifth Nerve.

F is the dorsal spino-cerebellar tract immediately ventral to this, and G is the

ventral tract.

clear that it constitutes the great tract of connection between the cerebellar hemisphere, the bulb, and the spinal cord.

The restiform body becomes conspicuous above the level of the cuneate tubercle, and forms the lateral boundary of the lower or bulbar half of the floor of the fourth ventricle.

Internal Structure of the Medulla Oblongata. —Each half of the bulb is composed of grey nervous matter and tracts of white nervous matter.

Grey Matter. —The grey matter lies largely in the interior. Over the dorsal aspect of the upper or open part of the bulb, however, it comes to the surface, and covers the lower or bulbar half of the floor of the fourth ventricle.



THE NERVOUS SYSTEM


1457


As compared with the grey matter of the spinal cord, it presents mportant modifications, and its component parts are as follows:

1. Substantia or formatio reticularis.

2. A thick layer of grey matter around the central canal in the

lower or closed part of the bulb.


Fig. 886.—The Decussation of the Pyramids: Scheme representing the Passage of the Various Tracts from the Spinal Cord to the Medulla (L. Testut’s ‘ Anatomie Humaine ’).


a. Pons

b. Medulla Oblongata (anterior aspect)

c. Decussation of the Pyramids

d. Section of the Cervical Spinal Cord

1. Anterior Cerebro-spinal Tract

2. Lateral Cerebro-spinal Tract

3. Sensory Tract


3'. Nucleus Gracilis et Nucleus Cuneatus

4. Antero-lateral Intersegmental Tract

5. Anterior Pyramid

6. Fillet or Lemniscus

7. Posterior Longitudinal Bundle

8. Ventral Cerebellar Tract

9. Dorsal Cerebellar Tract


3. A thick layer of grey matter over the floor of the fourth

ventricle in the upper or open part of the bulb.

4. Substantia gelatinosa (nucleus of spinal tract, N. V.).

5. Nuclei of grey matter.

The modifications undergone by the grey matter of the bulb in ts lower or closed part are brought about by the decussation of the

92


























A MANUAL OF ANATOMY


1458

pyramids. The nerve funiculi of the lateral cerebro-spinal tract of the spinal cord, on one side as they are traced upwards, pass through the base of the ventral grey column of that side, and then cross in the lower part of the ventral median fissure of the bulb to the pyramid of the opposite side, of which they form the inner and larger part. The nerve funiculi of the tract of the other side are disposed in a similar manner. The ventral grey column of either side is thus broken up by the corresponding crossed pyramidal tract. Its basal part remains on the ventral and lateral aspects of the central canal, but its caput is detached and displaced laterally by the pyramid and olive of the same side (see Fig. 887).

The dorsal horn of grey matter is gradually displaced laterally and ventralwards, in the lower or closed part of the bulb, by the funiculus gracilis and funiculus cuneatus. Its basal part remains on the dorsal and lateral aspects of the central canal; its cervix is broken up into a network by intersecting nerve-fibres; and its caput is thereby detached.


Fig. 887.— Schematic Sections showing Decussation of Pyramids with the Destruction of Base of Ventral Grey Column (Testut).

The caput lies close to the detached caput of the ventral grey matter, but does not blend with it.

Substantia or Formatio Reticularis. —The grey matter of the detached caput of the ventral grey cornu is broken up into a network by intersecting nerve-fibres, which run longitudinally and transversely. This reticulum, augmented by the network formed in the cervix of the dorsal grey cornu, constitutes the substantia or formatio reticularis of the bulb. It lies deeply within the bulb, dorsal to the olive and pyramid of the same side, and it consists of grey matter, longitudinal and transverse nerve-fibres, and some nerve-cells.

The funiculi of the hypoglossal nerve, as they pass forwards to the ventro-lateral sulcus of the bulb, divide the formatio reticularis into two parts—lateral and medial (Fig. 891). The lateral portion is situated behind the olive, and is called the formatio reticularis grisea, from the large amount of grey matter, with nerve-cells, which it contains. The medial portion is situated behind the pyramid, and is












THE NERVOUS SYSTEM


1459


illed the formatio reticularis alba. It contains little grey matter nd few nerve-cells.

Central Grey Matter. —The grey matter which surrounds the jntral canal in the lower or closed part of the bulb is derived from le basal portions of the ventral and dorsal grey columns of the upper art of the spinal cord. In the upper or open part of the bulb this mtral grey matter spreads out and forms a thick layer over the wer or bulbar part of the floor of the fourth ventricle. The medial %rt of this layer represents the basal part of the ventral grey horn, id it contains the hypoglossal nucleus. The lateral part represents le basal part of the dorsal grey horn, and it contains vagus, glossoharyngeal, and vestibular nuclei.

The hypoglossal nucleus is frequently spoken of as ' morphologically continuous with ’ or ‘ representing ’ the ventral grey column above the cervical nerves. This continuity, however, is not an actual anatomical fact; it exists only in the site of ependymal zone origin of the neuroblasts concerned in forming the nuclei. The ordinary motor cells of the ventral grey column in the cord have been derived from the lower part of the ependymal zone, from which they have migrated to form the ventral portion of the marginal zone. Later, when the collections of neuroblasts in the ventral horn have already settled into something approaching their final arrangements, a secondary output of neuroblasts frees itself from the ependymal zone in the same region, but does not migrate any further; this, then, might be looked on as of the same ependymal or original value as the ventral cells, although not anatomically continuous with them. It is from this secondary formation, which is found in the cervical and hind-brain regions, that the hypoglossal nucleus is formed; possibly the sixth nucleus owns a like origin, but this cannot be said with certainty. The other nuclei mentioned in the preceding paragraph are not concerned in this development in any way.

Substantia Gelatinosa (Fig. 885).—This caps the detached and splaced caput of the dorsal horn of grey matter. Having increased

amount owing to the presence of root-fibres of the fifth nerves id lying close to the surface, it gives rise to the tuberculum gelatinosum, metimes referred to simplv as the ‘ spinal tract of the fifth nerve.

Nuclei of Grey Matter.— The nuclei, which will be considered in is place, are as follows:

1. Nucleus gracilis.

2. Nucleus cuneatus.

3. Olivary nuclei.

4. Arcuate nucleus.

5. Nucleus lateralis.

The nucleus gracilis is a collection of grey matter within the funiclis gracilis. For the most part it is connected with the grey matter


A MANUAL OF ANATOMY


1460

on the dorsal and lateral aspects of the central canal, and it ma] be regarded as being in large part an extension from the basal par of the dorsal grey cornu. It is elongated, and increases in size a: it ascends. It gives rise to the prominence of the funiculus gracilis and to the clava, and the fibres of the funiculus gracilis, as they ascend terminate at intervals around the cells of the nucleus (see Fig. 885).

The nucleus cuneatus is a collection of grey matter within th< funiculus cuneatus. It is a direct extension from the basal part 0


Fig. 888.—The Formatio Reticularis of the Medulla Oblongata, showi by a Horizontal Section passing through the Middle of the Olivary Body (Demi-schematic) (L. Testut’s ‘ Anatomie Humaine ').


1. Anterior Median Fissure

2. Fourth Ventricle

3. Formatio Reticularis 3'. Reticularis Alba

3". Reticularis Grisea

4. Raphe

5. Anterior Pyramid

6. Lemniscus

7. Inferior Olive with the two

Accessory Nuclei


7'. Peduncle of Olivary Body

8. Hypoglossal Nerve 8'. Hypoglossal Nucleus

9. Vagus Nerve

g'. Terminal Nucleus of Vagus Nerve

10. External Dorsal Vestibular Nucleus

xx. Nucleus Ambiguus

12. Nucleus Gracilis


13. Nucleus Cuneatus

14. Caput of Posterior Cornu 14'. Lower Sensory Root of Fift

Nerve

15. Fasciculus Solitarius

16. External Anterior Arcuat

Fibres

16'. Arcuate Nucleus

17. Lateral Nucleus


the dorsal grey cornu, which lies on the dorsal and lateral aspect: of the central canal. Like the nucleus gracilis it is elongated, anc increases in size as it ascends. It gives rise to the prominence 0: the funiculus cuneatus and to the cuneate tubercle, and the fibre: of the funiculus cuneatus, as they ascend, terminate at interval: around the cells of the nucleus.


Lateral to the nucleus cuneatus there is a small collection of grey matter which is known as the external or accessory cuneate nucleus. It is on a highe: level than the decussation of the pyramids, and it may be regarded as a detachec portion of the substantia gelatinosa.






THE NERVOUS SYSTEM


1461


The olivary nuclei are associated with the olive, and are three in imber—inferior, and two accessory (medial and dorsal).

The superior olivary nucleus is situated in the dorsal or tegmental part of 5 pons, and is not developmentally associated with those now dealt with.


The inferior olivary nucleus, which is the chief nucleus, is situated thin the olive. As seen in transverse sections through the olive, appears (Fig. 889) as a wavy lamina of grey matter, curved in such a inner as to form an incomplete capsule, which encloses white matter.


Nucl. Grac.


Nucl. Cun.

— Fasc. Solitar.

Sp. Nucleus of Trigeminal Sp. Root Fibres of Trigeminal Med. Longit. Fasc. (Post. Longit. Bundle) Nucl. Ambiguus Lateral Nucleus

Ant. Sp. Cerebellar Fasc. (Gowers)

Dorsal Acc. 01 .


ig. 889.—Section through the Lower Half of Inferior Olive (shows also the Medial and Dorsal Accessory Olives).


racile and cuneate nuclei are seen in position, but spinal tract of fifth is separated from surface by fibres passing to inferior peduncle; these are dorsal spinocerebellar and fibres from olive from opposite side; some fibres from olive pass between the nucleus and the nerve tract. Arrows show the direction of fibres on one side. The upper ones come from the dorsal nuclei and fi th nucleus, and run ventrallv to decussate. The lower fibies are running dorsally, and come mainly from opposite olive, and some from same side.


he open part of the capsule is called the hilum, and is diiected )wards the median line, but it stops short of either end of the nucleus.

great many nerve-fibres pass through the hilum, some inwards nd others outwards, and these form what is known as the olivary eduncle. The wavy lamina is traversed by nerve-fibres..

The medial accessory and dorsal accessory olivary nuclei are situated n the medial and dorsal aspects respectively of the inferior or chiet fivary nucleus, from which, however, they are distinct. Each consts of a band of grey matter, and the upper part of the medial xessory nucleus lies opposite the hilum of the chief nucleus.












A MANUAL OF ANATOMY


1462

Structure of Inferior Olivary Nucleus. —The wavy lamina consists of many small nerve-cells and nerve-fibres which traverse it. The axons of the nerve-cells leave the nucleus as nerve-fibres, and pass to the raphe of the bulb. Some of the nerve-fibres which traverse the wavy grey lamina terminate in connection with its cells, and other fibres pass through it (see Fig. 889).

There are at least two fibre tracts (in addition to those passing into the inferior peduncle) which connect the inferior olive with more distant parts of the nervous system, and are recognizable in sections; little is actually known about them otherwise. The smaller one (olivo-spinal or Helweg’s tract) lies on the surface of the lower medulla and cord immediately in front of the ventral spino-cerebellar fibres. The upper tract, much larger and longer, is the tractus pallido-rubro-olivaris, a name describing its apparent connections.

The structure of the two accessory olivary nuclei corresponds to that of the chief or inferior olivary nucleus.

Arcuate Nucleus. —This nucleus (seen in Fig. 889) consists of a lamina of grey matter which lies upon the ventral aspect of the pyramid of the bulb above the level of the decussation of the pyramids, and beneath the anterior superficial arcuate fibres as they arch outwards over the pyramid after emerging from the ventral median fissure. Superiorly it lies over the medial aspect of the pyramid close to the ventral median fissure. It contains small nerve-cells, in connection with which some of the anterior superficial arcuate fibres terminate, whilst others arise as axons of the cells, and many of them pass over the nucleus without entering it.

Fibres of various sorts, which may be termed in general circumolivary, may be found turning over the lower part of the olive. Some are superficial arcuate fibres, as just described, but others may come apparently from the pyramid, and others again, associated with the ponto-bulbar body, may be really of the nature of aberrant pontine fibres.

Nucleus Lateralis. —This is a special collection of nerve-cells in that portion of the formatio reticularis grisea which lies on the dorsolateral aspect of the olive. It is situated deeply between the olive and the substantia gelatinosa (see Fig. 889).

White Matter of the Medulla Oblongata. —The white matter is situated chiefly on the surface. Over the dorsal aspect of the upper or open part of the bulb, however, the grey matter comes to the surface, and covers the lower or bulbar half of the floor of the fourth ventricle. The white matter is disposed in tracts or strands which are chiefly longitudinal, but a few run transversely in an arched manner. The tracts are as follows:

1. Pyramidal tract (cerebro-spinal tract).

2. Dorsal spino-cerebellar tract (direct cerebellar tract).

3. Ventral spino-cerebellar tract (tract of Gowers).


/


THE NERVOUS SYSTEM


1463

4. Restiform body (inferior cerebellar peduncle).

5. Funiculus cuneatus.

6. Funiculus gracilis.

7. Medial or posterior longitudinal bundle.

8. Tecto-spinal tract.

g. Rubro-spinal tract.

10. Spino-tectal tract.

11. Superficial arcuate tract.

12. Deep arcuate tract.

13. Fillet (lemniscus).

14. Vestibulo-spinal tract.

15. Olivo-cerebellar tract.

The pyramid of either side and the decussation of the pyramids rave been already described. It may, however, be again stated Fat the path of their motor nerve-fibres is downwards into the spinal

ord.

The pyramidal tract has descended from the pons.

Posterior (or Direct) Spino-cerebellar Tract. —This tract extends upwards from the lateral column of the spinal cord. It traverses

he lower part of the lateral area of the bulb nearly as high as the

ower part of the olive, and immediately anterior to the tuberculum ^elatinosum, after which it passes backwards and upwards into the inferior peduncle, of which it forms a part (Fig. 883).

Anterior Spino-cerebellar Tract. —This tract, like the dorsal or lirect spino-cerebellar tract, extends upwards from the lateral column if the spinal cord. It is situated chiefly on the dorsal aspect of the ilive, but some of its fibres appear close to the outer side of that body. Whilst the dorsal spino-cerebellar tract passes into the restiform body, and so reaches the cerebellar hemisphere directly, the ventral spino-cerebellar tract is continued upwards into and beyond the pons before reaching the cerebellar hemisphere.

Restiform Body.— The restiform body, or inferior peduncle of the cerebellum, is situated on the dorsal aspect of the bulb in its upper ir open part, the funiculus gracilis and funiculus cuneatus occupying the dorsal aspect in its lower or closed part. It succeeds to the clava ind cuneate tubercle, in which these two funiculi respectively end, but it receives no nerve-fibres from the funiculi. It makes its first appearance in relation to the nucleus cuneatus, and above the cuneate tubercle it is a conspicuous massive bundle, which forms the lateral boundary of the lower or bulbar half of the floor of the fourth ventricle. Its course is upwards, outwards, and then suddenly backwards. It sinks into the corresponding hemisphere of the cerebellum.

This peduncle is composed of fibres which are derived from the

following sources:

1. The olivo-cerebellar fibres of the inferior olivary nucleus of the opposite

side

2. The posterior cerebellar tract of the lateral column of the spinal cord of

the same side.


  • 4^4


A MANUAL OF ANATOMY


3. The anterior superficial arcuate fibres from the nucleus gracilis and

nucleus cuneatus of the opposite side.

4. The posterior arcuate fibres from the nucleus gracilis and nucleus

cuneatus of the same side.

5. Vestibular fibres from the vestibular nuclei of the vestibular division of

the auditory nerve.

The restiform body, from its composition, serves as an important means of connection between the cerebellar hemisphere superiorly and the medulla oblongata and spinal cord inferiorly.

Funiculus Cuneatus and Funiculus Gracilis. —These tracts are prolonged upwards from the posterior column of the spinal cord. As stated, each contains a grey nucleus, around the cells of which the corresponding sensory nerve-fibres terminate at intervals as they ascend. Towards the clava and cuneate tubercle the fibres become few and are spread over the clava and cuneate tubercle, finally ending in connection with the cells of the grey nuclei which give rise to these prominences (Fig. 885).

Posterior Longitudinal Bundle. —The fibres of this bundle ( fasciculus longitudinalis medialis ), when followed downwards into the anterior column of the spinal cord on the same side, represent the fibres of the ventral intersegmental tract. As these fibres are followed into the lower part of the bulb they form a bundle, which lies close to the median raphe and directly dorsal to the corresponding pyramid. This strand represents the longitudinal bundle in the lower part of the bulb. The deep arcuate fibres, to be presently described, pass obliquely through it to the median line, where they decussate with those of the opposite side. This decussation takes place in the interval between the right and left dorsal longitudinal bundles. Having now reached the other side, the deep arcuate fibres take an upward course, close to the median line, as the medial lemniscus. The dorsal longitudinal bundle and fillet are therefore now closely related to one another in the lower part of the bulb, both lying dorsal to the pyramid, the fillet lying close to the raphe.

In the upper part of the bulb the two tracts become distinct. The posterior longitudinal bundle is displaced dorsalwards during the formation of the fillet, and it comes into contact with the grey matter on the floor of the fourth ventricle, whilst the lemniscus lies on the dorsal aspect of the pyramid.

The posterior longitudinal bundle is prolonged into the ventral column of the spinal cord on the same side, where it is represented, as has been said, by the ventral intersegmental fibres.

A ventral or anterior longitudinal bundle (tecto-spinal tract) is described as lyi n g on the ventral aspect of the dorsal or posterior longitudinal bundle. This bundle, however, is not well defined. It descends into the anterior column of the spinal cord, and is accompanied by the ponto-spinal tract, the fibres of which spring from the cells of the formatio reticularis of the pons.

Arcuate Tracts. —These tracts form two goups—superficial and deep.


THE NERVOUS SYSTEM


1465


The superficial arcuate fibres are arranged in two sets—anterior md posterior.

The anterior superficial arcuate fibres arise from the nucleus gracilis and nucleus cuneatus of the opposite side, and a few arise from the arcuate nucleus of the same side. At the median line they decussate with those of the opposite side, and emerge at the ventral median fissure, where many of them arch over the medial and ventral aspects of the pyramid. Others pierce the pyramid, whilst some emerge at the ventro-lateral. sulcus between the pyramid and olive. The fibres now pass outwards and dorsalwards, some arching over the lower part of the olive, and finally enter the restiform body.

The posterior superficial arcuate fibres arise from the nucleus gracilis and nucleus cuneatus of the same side, and they enter the restiform body also of the same side.


Trigem. N.

Oblique Fasc.

Facial N.

Aud. N. Flocculus

Circumoliv. Fasc.


Basilar Groove


Pyramid


Fig. 890. —Front Aspect of Pons and Medulla, showing Oblique Fibres

of Pons and Arcuate Fibres on Medulla.


The deep arcuate fibres are disposed in two sets—lemniscal and olivo-cerebellar. The lemniscal deep arcuate fibres arise from the nucleus gracilis and nucleus cuneatus of the same side. They sweep forwards and inwards (Fig. 889) towards the raphe, passing obliquely through the dorsal longitudinal bundle. At the median line they decussate with those of the opposite side above the level of the decussation of the pyramids. Having reached the opposite side, the deep arcuate fibres change their course, and now pass upwards The ascending tract thus formed constitutes the medial lemniscus (or medial fillet).

The decussation which takes place between the deep arcuate fibres in the median line, immediately above the. decussation of the pyramids, is called the decussation of . the lemnisci (decussatio lemmscorum), or the superior sensory decussation, as distinguished from






1466


A MANUAL OF ANATOMY


the inferior sensory or spino-thalamic decussation, which takes place in the spinal cord.

The olivo-cerebellar deep arcuate fibres arise from the inferior olivary nucleus of one side. Emerging through the hilum, they pass across the median line to the opposite side. They then pass over or through the inferior olivary nucleus of that side, on the dorsal aspect of which they are collected into a distinct tract. This tract, arching backwards, applies itself to the restiform body on its deep aspect, and is thereby conducted to the cerebellar hemisphere. Its fibres terminate in the cortex of the vermis and cerebellar hemisphere. The olivo-cerebellar arcuate fibres constitute the olivo-cerebellar tract, which connects the inferior olivary nucleus of one side with the cerebellar hemisphere of the opposite side.

Lemniscus. —The lemniscus (or fillet), as seen in the bulb, is a wellmarked tract of fibres which lies on the dorsal aspect of the pyramid close to the raphe. As just stated, its fibres are derived from the lemniscal deep arcuate fibres of the opposite side. In the lower part of the bulb the fillet and posterior longitudinal bundle are closely related. In the upper part of the bulb, however, as already said, the posterior longitudinal bundle is displaced dorsalwards by the developing fillet, and the fillet, now distinct from the longitudinal bundle, lies on the ventral aspect of that bundle, and on the dorsal aspect of the pyramid. The ventral region of the bulb is thus traversed by four longitudinal tracts, all of which lie close to the median line. These tracts are related to each other in the following order from before backwards (ventro-dorsally):

Pyramid.

Fillet.

Tecto-spinal.

Posterior longitudinal bundle.

Olivo-cerebellar Tract.— This tract has already been described in connection with the olivo-cerebellar deep arcuate fibres.

Raphe of the Medulla Oblongata. —The raphe of the bulb occupies the median plane above the decussation of the pyramids, and is composed of fibres which, for the most part, cross obliquely from one side to the other. These fibres represent (1) the anterior superficial arcuate fibres, (2) the lemniscal deep arcuate fibres, and (3) the olivocerebellar deep arcuate fibres. A few fibres pass ventro-dorsally, and some are disposed longitudinally. The fibres are therefore arranged in an intersecting manner.

Central Canal of the Medulla Oblongata. —The central canal of the spinal cord is prolonged upwards through the lower or closed part of the bulb. As it ascends it is gradually displaced backwards, first by the decussation of the pyramids, and afterwards by the decussation of the lemnisci. It is surrounded by a thick layer of grey matter, which is derived from the basal portions of the ventral and dorsal grey horns of the spinal cord, Superiorly, at the level of the obex,


/


THE NERVOUS SYSTEM


1467


it opens into the lower part of the fourth ventricle in the angle between the two diverging clavse. The grey matter which surrounds the canal is now spread out, and forms a thick covering over the lower part of the ventricular floor, as has been said already.

Areas of Flechsig. —These areas involve the whole substance of the bulb, and are mapped out by the funiculi of the hypoglossal and vagus nerves. Seen in transverse section, these funiculi lie near each other as they arise from their nuclei in the grey matter of the lower part of the floor of the fourth ventricle. As the funiculi of the hypoglossal nerve pass forwards and those of the vagus nerve outwards they diverge from each other, and the substance of the bulb is thereby divided into three segments, which constitute the areas of Flechsig — ventral, lateral, and dorsal (see Fig. 891).


Fig. 891. —Plan to illustrate the Three Areas of Flechsig, showing the

Main Structures in Each of These.


The ventral area lies between the raphe of the bulb and the funiculi of the hypoglossal nerve. Throughout its thickness this area contains the following structures:

The pyramid and arcuate nucleus (Fig. 891, P).

The lemniscus, decussating (L).

The posterior longitudinal bundle (B).

The formatio reticularis alba.

The lateral area lies between the funiculi of the hypoglossal nerve and those of the vagus nerve. Throughout its thickness this area contains the following structures:

The olive and inferior olivary nucleus.

The nucleus lateralis (NL).

The nucleus ambiguus (to be afterwards described) (NA).

The formatio reticularis grisea.

The dorsal area is the region behind the funiculi of the vagus nerve. Throughout its thickness this area contains the following structures:

The inferior peduncle.

The upper part of the cuneate nucleus (C).

The descending root of the vestibular nerve ^ 'po be afterwards

The fasciculus solitarius (S) \ described.

The spinal root of the fifth cranial nerve (V) )

The substantia gelatinosa (G).





1468 A MANUAL OF ANATOMY

Course of Chief Nerve Funiculi of Spinal Cord through Medulla Oblongata. Spinal Cord. Medulla Oblongata.

Posterior Column.

Column of Goll (fasciculus gracilis).

Column of Burdach (fasciculus cuneatus).

Lateral Column.

(Crossed) lateral cerebro-spinal tract.

Anterior cerebro-spinal tract.

Dorsal (or direct) spino - cerebellar tract.

Ventral (or indirect) spino-cerebellar (tract of Gowers).

Prepyramidal or rubro-spinal tract.

Lateral intersegmental.

Anterior Column.

Anterior cerebro-spinal tract.

Tecto-spinal tract.

Ventral intersegmental.

Anterior marginal bundle (of Lowenthal).

Development of Medulla Oblongata.— The bulb is developed from the myelencephalon, which is the caudal division of the rhombencephalon.

2. The Pons.

The pons (Varolii) is situated above the medulla oblongata, and between the hemispheres of the cerebellum. With the exception of the inferior peduncles, all parts of the medulla oblongata are prolonged into it. The pons presents two surfaces (ventral and dorsal) and two borders (upper and lower). The ventral surface (Fig. 890) rests upon the upper part of the basilar groove of the occipital bone and the dorsum sellae of the sphenoid. It is convex from side to side, and from above downwards, and has a transversely striated appearance, due to the disposition of its superficial fibres. Along the median line it presents the basilar groove, which extends from the lower to the upper border, and lodges the basilar artery. On either side of this groove the ventral surface is rendered prominent by the prolongation upwards of the pyramids of the medulla oblongata, and the basilar groove is chiefly due to this circumstance. The sensory and motor roots of the fifth nerve, lying close together, appear on the lateral aspect of the ventral surface, the small motor root being the upper of the two. The portion external to these two nerveroots constitutes the middle peduncle of the cerebellum. It is composed of the transverse fibres of the pons, which pass backwards and laterally into the corresponding cerebellar hemisphere.


Funiculus gracilis and nucleus

gracilis.

Funiculus cuneatus and nucleus

cuneatus.


Inner three - quarters of opposite pyramid.

Outer one-quarter of pyramid of same side.

Lateral area below olive, and inferior peduncle.

Lateral area below olive, and formatio reticularis.


Outer one-quarter of pyramid of same side.

Posterior longitudinal bundle.


THE NERVOUS SYSTEM


1469


The dorsal surface is directed towards the cerebellum. It presents a triangular area which is covered with grey matter. This area is continuous with the dorsal surface of the upper or open part of the medulla oblongata, and it forms the upper or pontine part of the floor of the fourth ventricle. On either side it is bounded by the superior peduncle of the cerebellum as it passes upwards and inwards.

The upper border is slightly depressed at the centre, and on either side of the median depression it slopes outwards and downwards towards the middle peduncle of the cerebellum. The crura cerebri, right and left, sink into the pons at the upper border.


Internal Structure of the Pons. —dhe pons is composed of a large ventral and a small dorsal part.

Ventral Part.— This portion consists of (1) bundles of transverse fibres, (2) bundles of longitudinal fibres, and (3) a large amount ot


grey matter. , , ,, £ •

The bundles of transverse fibres intersect the bundles of longitudinal fibres, and on either side they are collected into e mi e peduncle of the cerebellum, which enters the corresponding cerebellar hemisphere. Some of the transverse fibres arise in, e cot ex of the cerebellum as the axons of the cells of Purkinje, an 1 terminate in the pons in arborizations round the cells of the nucleus pontis, mostly on the opposite side to that on which they arise Other transverse fibres arise in the pons as the axons of of the nucleus pontis on one side. They then cross to the other







I 47 °


A MANUAL OF ANATOMY


Corpora Mamillaria


side, and enter the cerebellar hemisphere of that side, where they terminate in arborizations in the cortex. The fibres, therefore, of which the middle peduncle of the cerebellum is composed may be regarded as being of two kinds—namely, efferent and afferent. The efferent fibres arise in the cerebellar cortex and terminate in the pons, whilst the afferent fibres arise in the pons and terminate in the cerebellar cortex.

The bundles of longitudinal fibres in each half of the ventral part of the pons are derived from the breaking up of the crusta or basis

pedunculi of the corresponding crus cerebri, which enters the pons at its upper border. Most of these bundles are collected together at the lower border of the pons, and form the pyramid of the medulla oblongata on the same side. Certain of the fibres of the basis pedunculi, however, terminate in the pons as follows: (i) some end in arborizations around the cells of the motor nucleus of the fifth cranial nerve, the nucleus of the sixth cranial nerve, and the nucleus of the seventh cranial or facial nerve ; and (2) others end in arborizations around the


Basis Pedunculi Cerebri --* 31 ; Locus Perforatus Posterior


Right Pyramidal Tract

Transverse Fibres of Pons

Middle Peduncle of Cerebellum


minL

Decussation of the Pyramids Ard :

■ f

Fig. 893.—Dissection of the Pons, showing the Course of the Pyramidal Tracts of the Medulla Oblongata (Hirschfeld and Leveille).

P., right pyramid; O.B., right olivary body.


cells of the nucleus pontis, all of the same side.


The fibres to cranial motor nuclei may run a more aberrant course, leaving the basis pedunculi in the mid-brain and running in the tegmentum of the pons to decussate and reach their objectives. Some also run a recurrent course, leaving the pyramid below the pons and turning upwards deeply.

The grey matter of the pons, which is large in amount, occupies the intervals between the intersecting transverse and longitudinal bundles, and contains small multipolar nerve-cells. It is known as the nucleus pontis, and is continuous with the arcuate nuclei of the medulla oblongata.

Corpus Trapezoides or Trapezium. —The trapezium is a fairly thick layer of transverse fibres on either side, which have no connection with the corresponding middle peduncle of the cerebellum. The fibres are situated in the lower part of the pons dorsal to the pyramidal bundles. Within the trapezium are large multipolar cells, which constitute the nucleus of the trapezium. The fibres of the trapezium arise chiefly as the axons of the cells of the ventral cochlear




THE NERVOUS SYSTEM


1471


mcleus, and also of the dorsal cochlear nucleus (or tuberculum icusticum), in which nuclei the fibres of the cochlear division of the mditory nerve terminate, Some of the fibres arise from the superior )livary nucleus; others are the axons of the cells of the nucleus of

he trapezium; whilst a third set (auditory strice) arise from the
uberculum acusticum of the opposite side. Certain of the fibres


Fig 8q4—Vertical Transverse Section through the Upper Part of the Pons and Fourth Ventricle (from L. Testut’s ‘ Anatomie Humaine,’ after Stilling).


1. Fourth Ventricle

2. Superior Velum

3. Superior Root of Fifth Nerve

4. Nerve-cells which accompany this Root

5. Posterior Longitudinal Bundle

6. Formatio Reticularis

7. Lateral Fissure of Isthmus


8. Section of Superior Cerebellar Peduncle 9,9. Medial and Lateral Portions of the Lemniscus

10, 10. Transverse Fibres of the Pons

11, 11. Longitudinal Fibres of the Pons

12. Raph6

V. Fifth Nerve


the trapezium terminate in the superior olivary nucleus, but the

laioritv cross the median plane, where they decussate with those E the opposite side. Having crossed to the opposite side, they ecome longitudinal, and form a well-marked ascending tract in the orsal part of the pons, called the lateral lemniscus, which lies on the

uter side of the main or medial fillet. . ,

Dorsal or Tegmental Part of the Pons.— This portion is divided ito two symmetrical halves by a median raphe, which is continuous ith that of the upper or open part of the medulla oblongata It insists of formatio reticularis, which is continued upwards from re formatio reticularis of the bulb. The formatio reticularis of the












1472


A MANUAL OF ANATOMY


dorsal part of the pons contains certain tracts of nerve-fibres and nuclei, with which important nerves are connected. These are so complicated that it is convenient to divide the dorsal part of the pons into two regions—lower and upper.

Lower Region. —This region corresponds to the level of the trapezium in the ventral part of the pons, and succeeds the upper end of the bulb. The inferior peduncle of the bulb lies for a short distance on the lateral aspect of this region, but soon passes backwards and sinks into the hemisphere of the cerebellum.

The tracts and nuclei of the formatio reticularis of the lower region, which will be described in this place, are as follows:

1. Spinal sensory root of the fifth cranial nerve.

2. Motor nucleus of the facial nerve.

3. Superior olivary nucleus.

4. Nucleus of the sixth cranial nerve.

5. Posterior longitudinal bundle.

6. Rubro-spinal tract.

7. Tecto-spinal tract.

8. Lemniscus.

The funiculi of the spinal or descending sensory root of the fifth cranial nerve appear ventro-medial to the mass of the inferior cere

Sixth Nucleus


Post. Long. Bundle Facial Nucleus

Corp. Trapez.


Basis Pontis


Fig. 895.—Nuclear Positions in Pons (Schematic).

bellar peduncle. Close to the inner side of this root, and accompanying it in its downward course, there is the inferior sensory nucleus of the fifth nerve, around the cells of which the fibres of the spinal or descending root of that nerve terminate at intervals. The inferior sensory nucleus is an upward prolongation of the substantia gelatinosa, and interiorly it extends to about the level of the second cervical spinal nerve (see Fig. 885).

The motor nucleus of the facial nerve is internal to the funiculi of the spinal root of the fifth nerve. It lies deeply in the lower region of the dorsal part of the pons on the dorsal aspect of the superior


Sensory Nucl. N.V. Motor Nucl. V.

Superior Olive Fifth Nerve











THE NERVOUS SYSTEM


1473


•livary nucleus. The motor fibres of the facial nerve arise as the xons of the cells of this nucleus (see Fig. 896).

The superior olivary nucleus is situated on the ventral aspect of he facial nucleus, and is close to the lateral part of the trapezium, he fibres of which arch round its ventro-lateral aspect. Some of hese fibres terminate in the superior olivary nucleus, whilst others .rise from its cells.

In connection with the superior olivary nucleus three other nuclei are lescribed: (1) an accessory superior olivary nucleus on the medial side of the )rincipal nucleus; (2) a lateral pre-olivary nucleus on the ventral aspect of the >rincipal nucleus; and (3) a medial pre-olivary nucleus on the ventral aspect of he nucleus of the trapezium.

The nucleus of the sixth cranial nerve lies immediately beneath he grey matter of the pontine part of the floor of the fourth ventricle, ind on the lateral side of the dorsal longitudinal bundle which separates he nucleus from the median raphe. It corresponds to that portion


supC- cerebellar peduncle.


facial colliculus _ _

nucleus of--., sixth H.

post- longitudbundie.

stalk of olive"'

median lemniscus


inferior! cerebellar middle j peduncle.

_\jai- vestibular

> x \ nucleus.

TV 7- 5 pinai root of V*- h n. facial nucleus


-facial nerve

^vestibular part ""'of 8th nerve.

. "Corpus trapezoides

""Supr- olivary nucleus

' oibducens nerve

pyramidal tract.

Fig. 896.—Diagrammatic Section through the Pons, to show Deep Origins of Sixth (Red) and Seventh (Black) Cranial Nerves.


f the facial colliculus which lies on the pontine part of the floor of he fourth ventricle directly above the auditory striae.

The medial or posterior longitudinal bundle lies close to the median iphe, and on the medial side of the nucleus of the sixth nerve. Like bat nucleus, it lies immediately beneath the grey matter of the pontine

art of the floor of the fourth ventricle. . , „

The lemniscus (medial, medial fillet) lies, as it <loes in the bulb, entral to the dorsal longitudinal bundle, but m the dorsal part of tl e ons the two strands are separated by a distinct interval occupied

93





  • 474


A MANUAL OF ANATOMY


by the rubro- and tecto-spinal tracts. It will have been noticed tha J in the spinal cord the tecto-spinal tract lies ventral to the rubro-spinal but later on it will be seen that the tectum or quadrigeminal region i: dorsal to the red nucleus. It is therefore clear that somewhere ir their course they must reverse their relative positions, and the rubro spinal become ventral to the tecto-spinal. Where this happens i: not at present clear; indeed, the exact relations of these and man} other tracts, such as the vestibulo-spinal, spino-thalamic, and spino tectal in the upper part of their course, are still under investigation The lemniscus occupies a broad area in that portion of the lowei region of the dorsal part of the pons which is contiguous to the ventra part. The area extends outwards from the median raphe.

Upper Region of the Dorsal Part of the Pons. —This region lies abovt the level of the trapezium in the ventral part of the pons. The tracts and nuclei of this region, which will be described in this place, are as follows:

1. Superior peduncle of the cerebellum.

2. Nuclei of the fifth cranial nerve.

3. Medial or posterior longitudinal bundle.

4. Medial fillet or lemniscus.

5. Lateral fillet or lemniscus.

The superior peduncle of the cerebellum, after emerging from the corresponding cerebellar hemisphere, lies on the lateral aspect of this region, where it forms the lateral boundary of the upper or pontine pari of the floor of the fourth ventricle. Its dorsal aspect is connected with that of its fellow of the opposite side by the superior medullary velum l and ventrally it sinks into the upper region of the dorsal part of the pons.

The pontine nuclei of the fifth cranial nerve are motor and sensory. The motor and main sensory roots are pontine, and the sensory root is prolonged down as the spinal tract, and up as the mesencephalic root.

The motor nucleus is situated close to the superior peduncle of the cerebellum at the lower part of the lateral margin of the upper or pontine part of the fourth ventricle. It lies near the surface, and the axons of its cells form many of the fibres of the motor root of the nerve.

The main sensory nucleus is situated deeply on the outer side of the motor nucleus, and on the ventral aspect of the superior peduncle of the cerebellum. Some of the fibres of the sensory root ascend and terminate in arborizations around the cells of this nucleus.

The lower or spinal sensory nucleus succeeds to the main sensory nucleus, and is a continuation upwards of the substantia gelatinosa. It is elongated, and extends into the upper part of the spinal cord to about the level of the second cervical nerve. It lies on the medial side of the spinal or descending sensory root of the fifth nerve, and the fibres of that root (. spinal tract) terminate at intervals in arborizations around its cells.

The mesencephalic root arises from groups of small cells which are placed in the grey matter of the mid-brain, beside the aqueduct,


THE NERVOUS SYSTEM


1475

extending up as far as the canal of the lower end of the superior

olliculus. Fibres run down from this part, but their actual disposition

n the fifth nerve is not yet settled.

There is some ground for supposing that this part of the nuclear arrangement of the fifth nerve is concerned with the reception of proprioceptive impulses from orbital muscles.

The posterior or medial longitudinal bundle has the same position in the upper region as it has in the lower region. It lies close to the median raphe, and immediately below the grey matter of the corresponding part of the floor of the fourth ventricle.

The main or medial lemniscus, like the main fillet in the lower region, lies in that portion of the upper region of the dorsal part of the pons which is near the ventral part, and it forms a layer of some breadth, extending outwards from the median raphe.

The lateral lemniscus is a strand of fibres which lies on the outer side of the medial fillet, and connects the cochlear nucleus with the opposite inferior corpus quadrigeminum. Associated with the lateral fillet, and lying between it and the medial fillet, there is a collection of nervecelis, called the nucleus of the lateral lemniscus.

Development of the Pons. —The pons is developed from the ventral and lateral walls of the metencephalon, which is one of the divisions of the rhombencephalon. The nuclear matter seems to be derived from the ponto-bulbar body, spreading over the surface of the neural tube.

3. The Cerebellum.

The cerebellum, or small brain, occupies the inferior occipital or cerebellar fossae of the occipital bone. It lies beneath the posterior parts of the hemispheres of the cerebrum, from which it is separated by a septum of the dura mater, called the tentorium cerebelli, and it is behind and above the medulla oblongata and pons. It is composed of white and grey matter, the white matter being situated in the interior, where it constitutes the medullary substance, and the grey matter being spread over the surface of the cortex. In appearance it is laminated or foliated, the laminae being separated from each other by parallel, slightly curved sulci. It is composed of two large lateral portions, called hemispheres, and a connecting median portion, termed the vermis, these parts being much more distinct below than above. When looked at from above it presents in the median line two notches, anterior and posterior. The anterior notch, which is wide, is known as the incisura semilunaris , and it contains the inferior pair of quadrigeminal bodies and the superior cerebellar peduncles. The posterior notch is narrow, and is occupied by the falx cerebelli. The most conspicuous sulcus of the cerebellum is the great horizontal fissure, which extends round the circumference, and passes for some distance into the interior. By means of this fissure the cerebellum is divided into two parts, upper and lower.

Relatively smaller in the new-born child, the cerebellum forms in the adult about an eighth of the whole mass of the brain.


I 47^


A MANUAL OF ANATOMY


The cerebellar surface is marked, as stated above, by the presence of numerous flattened or laminar gyri or folds, each fold being separatee from its neighbours by sulci of appreciable depth. Among these fissures are certain ones which are evident and deeper, and these car be taken to divide the surfaces into lobules or parts, which have some small descriptive value.


The presence of the foliated surface, and of certain striking appearances in different parts of the cerebellum, have led in the past to a wealth of terminology and description which, for the greater part, does not seem to be of much value or utility. Moreover, since these terms have in many instances come dowr from long past periods, they are archaic and fanciful. Thus it seems desirable to replace these with a short account of the cerebellar surface, broadly described, after which the older terms


Anterior Notch (Incisura Semilunaris)

Central Lobule

Anterior Crescentic Lobule

/

Primary Fissure

Posterior Crescentic Lobule


Postero-superior Fissure


f;A^SL Cor P° ,a Q ua drigemina


Postero-superior

Lobule


-Culmen Monticuli


.Preclival Fissure


Postclival Fissure


Postero-inferior Lobule


Clivus Monticuli


Posterior Notch Folium Cacuminis


Fig. 897.—The Cerebellum (Superior View).


and descriptions will be given in small print, for purposes of reference if required. Subsequently a short morphological consideration of the part can be added.

Upper Surface of the Cerebellum. —This surface presents in the median line the upper part of the vermis, known as the superior vermis (see Fig. 897). It extends from the incisura semilunaris to the posterior notch, and it forms a laminated elevation, which is higher in front than behind, the most prominent part being known as the monticulus cerebelli. On either side of the superior vermis the upper surface of each hemisphere inclines downwards to the circumference, and there is no distinct demarcation between it and the superior vermis.

This upper aspect is divided (Fig. 898) by two main fissures, primary and postclival, which are continued across the slight elevation of the superior vermis.


/



THE NERVOUS SYSTEM


x 4 77

The primary fissure (Fig. 898, PR) cuts across the vermis a little behind its highest point, the culmen. From this the fissure is continued with a slight forward curve on each side, to reach the horizontal fissure.

The fissure is termed ‘ primary ’ because it forms the posterior limit, at a fairly early stage, of the morphological entity, the anterior lobe.

The postlunate or postclival fissure (PC) is behind the primary fissure and below it; this is due to the descent of the vermis from the culmen, forming its ‘ declive * behind the primary fissure. The postclival fissure turns forward on each side with a bolder curve towards the horizontal fissure.


Fig. 898. —Upper Aspect of Cerebellum, with Main Subdivisions.

C, culmen; D, declive (or clivus); PR, primary fissure; PC, postlunate (or postclival) fissure; H, posterior end of horizontal fissure.

The anterior lobe lies above and in front of the primary fissure, including the parts of the vermis and lateral lobes as a continuous whole.

The posterior lunate lobe lies between the primary and postlunate fissures, and includes also the central vermis.

The posterior end of the horizontal sulcus (H) appears usually on this aspect of the cerebellum. It fails to reach the vermis, usually running into the postlunate sulcus.

The lobule which is seen on each side below the postlunate and above the horizontal fissure is frequently referred to as the superior crescentic lobule; it is also termed the superior (division of the) ansiform lobe.

The superior vermis is composed of five lobules, named, in order from before backwards, the lingula, central lobule, culmen monticuli, clivus monticuli, and folium cacuminis. The lingula is deeply placed, and consists of about four laminae or folia, which lie over the superior medullary



[478


A MANUAL OF ANATOMY


velum as it extends between the superior cerebellar peduncles. Its laminae may be continued on either side over the superior cerebellar peduncle, and, when this is so, the prolongation is known as the frenulum lingulae.

The central lobule is of small size, and lies at the bottom of the incisura semilunaris. It is separated from the lingula by the precentral fissure, and from the culmen monticuli by the postcentral fissure.

The culmen monticuli forms the summit of the superior vermis. It is composed of several laminae, and posteriorly is separated from the clivus by the preclival fissure.

The clivus monticuli represents the sloping part of the monticulus cerebelii. It is situated behind the culmen monticuli, and is composed of several laminae. Posteriorly it is separated from the folium cacuminis by the postclival fissure.

The folium cacuminis forms the posterior extremity of the superior vermis, and lies at the posterior notch, where it is placed above the great horizontal fissure.


i locculus


Biventral Lobule


Lobulus Gracilis 1 Great Horizontal

Fissure , I

t

Inferior Semilunar Lobule


Amygdala (Tonsil)


Pyramid Tuber Valvulae


-Pregracile Fissure — Mid-gracile Fissure —Post gracile Fissure -•-Small Horizontal Fissure


Fig. 899.— The Cerebellum (Inferior View).

1 he inferior semilunar lobule and the lobulus gracilis constitute the postero inferior lobule. Old terminology used.


The upper surface of each hemisphere is mapped out into lobules, which are continuous with the subdivisions of the superior vermis, with the exception of the lingula. These are called, in order from before backwards, the ala, anterior crescentic lobule, posterior crescentic lobule, and postero-superior lobule.

The ala is continuous with the central lobule, from which it is prolonged for a limited distance round the anterior part of the hemisphere in the region of the incisura semilunaris.

The anterior crescentic lobule is continuous with the culmen monticuli, and represents the anterior subdivision of the upper surface of the cerebellar hemisphere. It is limited posteriorly by a curved sulcus, called the anterosuperior fissure, which is continuous with the preclival fissure (fissura prima), and opens at the circumference into the great horizontal fissure. The right and left anterior crescentic lobules, together with the culmen monticuli, form the lobus culminis (see Fig. 897).

The posterior crescentic lobule is continuous with the clivus monticuli. It is limited in front by the antero-superior fissure, and behind by the postero-superior fissure, the latter being continuous with the postclival fissure, and opening at the circumference into the great horizontal fissure.








THE NERVOUS SYSTEM


1479


The right and left posterior crescentic lobules, together with the clivus monticuli, form the lobus clivi.

The postero-superior lobule (superior semilunar lobule) corresponds to, but is much more extensive than, the folium cacuminis. It is limited in front by the postero-superior fissure, and behind by the great horizontal fissure. The right and left postero-superior lobules, together with the folium cacuminis, form the lobus cacuminis.

Under Surface of the Cerebellum. —The under surface presents in

he median line a deep groove, called the vallecula, which is continuous

Dehind with the posterior notch. Anteriorly it lodges the medulla Dblongata, and lying in the bottom of it there is the lower part of the /ermis, which is known as the inferior vermis. The vallecula separates the two cerebellar hemispheres from each other, and the inferior vermis s separated on either side from the corresponding hemisphere by a furrow called the sulcus valleculce. The under surfaces of the hemi


Fig. 900.—Lower Aspect of Cerebellum, showing the (Inferior) Ansiform Lobe and the Paramedian Lobule or Tonsil; also the Flocculus.


spheres are markedly convex, and are received into the inferior occipital or cerebellar fossae of the occipital bone.

The inferior aspect of the cerebellum (Fig. 900) presents on the lateral lobes, near the margins, the greater part of the horizontal fissure (H). The two additional fissures shown in the figure are of quite secondary importance; the upper one of the two was taken formerly as the lower boundary of the ‘ inferior crescentic lobule (ISL.), but it is not necessary now to subdivide the inferior surface in this way, but rather to term all this curved surface the posterior or posteio-inferior lobe, or the inferior (part of the) ansiform lobe. #

The paramedian lobule or tonsil, however, stands out as a striking formation on each side of the ‘ posterior notch, and is not included in the name given to the rest of the inferior surface. The base of the tonsil is received in a cup-shaped concavity on the inferior and medial surface of the ansiform lobe, from which it is separated by a deep retrotonsillar fissure. The loosely foliated flocculus (FLOCC) is





1480


A MANUAL OF ANATOMY


visible on each side, outside and in front of the tonsil. The flocculus has a white ' stalk/ which is continuous with the inferior medullary vellum, making with this a large part of the bed of the hollow which contains the tonsil. This velum is connected centrally with the

  • nodule/ the terminal piece of the inferior vermis.

The inferior vermis is composed of four lobules, named, in order from behind forwards, tuber valvulse, pyramid, uvula, and nodule.

The tuber valvulae (tuber posticum) forms the posterior part of the inferior vermis, and is composed of several laminae. On either side it is prolonged into the corresponding hemisphere, and becomes continuous with the postero-inferior lobule. It is the only part of the inferior vermis which is prolonged into the cerebellar hemispheres.

The pyramid is situated in front of the tuber valvulae. It presents about four laminae, and is separated by deep sulci from the tuber valvulae behind and the uvula in front, whilst on either side it is separated from the cerebellar hemispheres by the sulcus valleculae. Laterally it is connected with the biventral lobule of the hemisphere by means of a faint ridge, but this lies low in the sulcus valleculae as it crosses.

The uvula is situated in front of the pyramid, and between the amygdalae or tonsils of the hemispheres. It is triangular, the base being directed backwards, and it consists of several laminae. It is separated on either side from the hemisphere by the sulcus valleculae. Laterally its narrow part is connected with the amygdala by a ridge of grey matter, but this lies low in the sulcus valleculae as it crosses. This ridge is notched at intervals, and is called the furrowed band.

The nodule forms the anterior part of the inferior vermis, and is composed of several laminae, which are largely concealed by the uvula. It is connected on either side with the flocculus by a thin semilunar band of white matter, which is the lateral portion of the inferior medullary velum.

The fissures of the inferior vermis are three: postpyr amidal, between the pyramid and the tuber valvulae; prepyramidal (fissura secunda), between the pyramid and the uvula; and postnodular, between the nodule and the uvula.

The under surface of each hemisphere is mapped out into four lobules, which are called, from behind forwards, the postero-inferior lobule, the biventral lobule, the amygdala, and the flocculus.

The postero-inferior lobule is situated at the back part of the under surface of the hemisphere. It is divided into four curved parts by three curved Assures. The anterior two parts are known as the lobulus gracilis, and the posterior two as the inferior semilunar lobule. The right and left postero-inferior lobules, together with the tuber valvulae, form the lobus tuberis.

The biventral lobule is composed of curved laminae, and is somewhat triangular. The pointed end is directed backwards and inwards, and it is connected with the pyramid by a faint ridge, which lies low in the sulcus valleculae. The base is directed forwards towards the flocculus. The lobulus gracilis lies external to it, and the amygdala is on its inner side. The biventral lobule is divided by a sulcus into two portions, outer and inner; hence the name ‘ biventral.’ The right and left biventral lobules, together with the pyramid, form the lobus pyramidis.

The amygdala (tonsil) forms a conspicuous prominence between the uvula and the biventral lobule. It is situated in a depression of the vallecula, which is known as the nidus avis (‘ bird’s nest ’), and its long axis is almost sagittal. It is connected with the narrow part of the uvula by the furrowed band in the sulcus valleculae. The right and left amygdalae, together with the uvula, form the lobus uvulae.

The flocculus (subpeduncular lobule) is a small irregular lobule which


THE NERVOUS SYSTEM


1481

is situated between the front of the biventral lobule and the middle peduncle of the cerebellum. Internally it is connected with the nodule by the lateral portion of the inferior medullary velum. The right and left flocculi, together with the nodule, form the lobus noduli.

In the foetus a structure, known as the paraflocculus, lies behind and to the outer side of the flocculus, and occupies a depression in the petrous bone. In the lower monkeys it persists throughout life, but in man it atrophies after birth.

The fissures of the under surface of each hemisphere are: (1) a continuation of the postnodular sulcus, between the biventral lobule and the flocculus; (2) a continuation of the prepyramidal sulcus, between the am yfl ( lala an< d the biventral lobule; (3) the pregracile, or anterior arcuate sulcus, between the biventral lobule and the lobulus gracilis; (4) the midgracile, or middle arcuate sulcus, within the lobulus gracilis; (5) the postgracile, or posterior arcuate sulcus, between the lobulus gracilis and the inferior semilunar lobule; and (6) the small horizontal sulcus within the inferior semilunar lobule.

Cerebellar Morphology.—Extensive examination of the types and varieties of the cerebellum found in different classes of animals has gradually established the fundamental parts of this organ. It has )een shown to consist essentially of three lobes—anterior, middle, and bosterior—of which the anterior is the most primitive, the middle and posterior appearing in higher forms; in birds both these are present, md in mammals reach a more extensive development, while in man md the higher mammals the middle lobe reaches its most expanded

orm, varying much in the different orders of mammals below these,

[t may be added that the vermis is to be looked on as a more primitive md older part of the organ than the lateral lobes, in which the paired donations exhibit much variety.

The anterior lobe is represented in man by that portion of the cerebellum lying above and in front of the primary fissure; this has received ts name from this relationship, and various names have been given

o the part thus marked off, known now as the anterior lobe. The

obe includes the vermis in this part, as far back as behind the culmen, vhere the fissure cuts through it.

The middle lobe is a simple lens-shaped formation (Fig. 901 a), as

een on the surface in lower vertebrates. In the mammals, however,

t is found to present a simple transverse bar immediately behind the brimary fissure, but behind this it shows medial and lateral parts, of vhich the lateral portions exhibit (Fig. 901 a) two main divisions—an ipper or anterior one, curved on itself, and hence termed the ansiform obule \ and a lower one (continuous with the ansiform lobule) placed beside the median formations, and hence named the paramedian obule.

The posterior lobe is also composed of a median part (posterior nedian lobule) and two lateral portions; these consist on each side of 1 flocculus and paraflocculus, as illustrated in the figure.

The human cerebellum possesses a relatively simple anterior lobe, is pointed out above. There is also a recognizable ‘ transverse bar,’ narking the upper portion of the middle lobe, in the so-called ‘ lobulus Implex ' (posterior lunate lobe or posterior crescentic), which includes


1482


A MANUAL OF ANATOMY


the central declive. It is behind this that the middle lobe is particularly concerned in forming the greater part of the human lateral lobe from the ansiform lobule on each side, while the posterior lobe remains centrally, but degenerates in part in its lateral portions.


Fig. 901A.—Illustrations of Cerebellar Structural Morphology, based

on Figures by Ingvar.

1, higher reptile; 2, bird; 3, mammal; A, M, P, anterior, middle, and posterior lobes; ANS, PM, ansiform and paramedian lobules; F, PF, flocculus and paraflocculus.

The schematic drawings in Fig. 901B may make this transformation clearer. In the first scheme the recognition of the fundamental parts, as already described, is evident and straightforward; the anterior lobe (A) is separated by the primary fissure from the ‘ lobulus simplex,' marked by the upper M; the lower M indicates the lower portion of the


Fig. 901 b.— To illustrate Hypothetical Stages in the Evolution of

Form of Human Cerebellum.

(References as in previous figure.)


middle lobe, with its two lateral pieces consisting of ansiform (ANS) and paramedian (PM) lobules. The overgrowth of the ansiform lobule accounts for the greater part of the lateral lobe (behind the lobulus simplex), as shown in the second figure, while the paramedian lobule remains as the ‘ tonsil.' The great ansiform enlargement is naturally






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1483

in a doisal and lateral direction mainly, so that the paramedian lobule is overlapped, and finds itself on the anterior aspect of the lower and median part of the enlargement.

The posterior lobe, stippled, is seen (as in the primitive forms, Fig. 901A) to have a central and two lateral pieces; these show floccular (F) and parafloccular (PF) enlargements. In the human foetus these ire represented, but the paraflocculus is lost, and the flocculus remains done in the adult condition, connected still with the median part of the posterior lobe.

When estimating the comparative values of the parts of the cerebellum, as above, it must be remembered that the growing thickness of the organ affects not only the lateral, but also the median parts; thus, the vermis is very thick in the middle lobe and fades rapidly in the bosterior lobe, so that this last is turned down and comes to look iownwards and forwards. 1 his is associated with the overgrowth bf the ansiform lobule, whence the paramedian lobule is visible from below and in front, and not from behind, as in the scheme; it is covered behind by the increasing growth of the ansiform lobule extending medially behind it and the buried posterior derivatives.

To sum up shortly: the lateral lobes of the cerebellum are, for their posterior, lateral, and greater part, overgrowths of the ansiform portion of the middle lobe, the tonsil being paramedian. Above this is another part (lobulus simplex, upper crescentic) of the middle lobe, separated by the primary fissure from the simple anterior lobe, the oldest lobe of the organ. The vermis is represented in both anterior and middle lobes as the central portion, thickened very much in these parts, but getting rapidly smaller (and hence reversed, as it were) in the posterior lobe. The flocculus is the remnant of the lateral portion of the posterior lobe.

The vermis in front of the primary fissure is the central part of the interior lobe, behind this fissure, down to and including the declive; t belongs to the upper portion (lobulus simplex) of the middle lobe,

he lower part of which includes the ‘ tuber vermis ' and ends at the

prepyramidal fissure/ The central part of the posterior lobe includes

he pyramid, uvula, and nodule, and it is of interest to note that these

barts are particularly connected (Holmes and Stewart) with the medial iccessory olive, the oldest part of the inferior olivary structures; the arge inferior olive of higher mammals has appeared with the lateral growth of the cerebellum in them, and in less direct connection with

he development of the cerebral cortex.

Peduncles of the Cerebellum.—The peduncles are three in number Dn either side—superior, middle, and inferior—and they are composed bf fibres which enter or leave the central white medullary substance.

The superior peduncles (brachia conjunctiva) are largely composed bf efferent fibres, and are at first concealed from view by the upper br anterior portions of the hemispheres. After they leave the hemi

i 4 8 4


A MANUAL OF ANATOMY


spheres they pass upwards on the lateral aspects of the dorsal surface of the pons in a converging manner towards the quadrigeminal bodies (or colliculi of mid-brain). They form the lateral boundaries of the upper part of the floor of the fourth ventricle, and by their convergence they project slightly over that part of the ventricle, so as to take part in its roof. The superior medullary velum extends between the two peduncles, and closes the interval between them. On reaching the inferior pair of quadrigeminal bodies the two peduncles pass beneath them and enter the mesencephalon, where their course will be subsequently described (see p. 1553). Most of the fibres of each superior peduncle are derived from the corresponding nucleus dentatus, but a few come from the grey matter of the cerebellar cortex. In addition to these there are the fibres of the ventral (or indirect) cerebellar tract (of Gowers).

The middle peduncles are of large size, and are formed by the transverse fibres of the pons, these being gathered together on either side into a large bundle, which passes backwards and laterally into the white central medullary substance of the corresponding hemisphere. The fibres of each middle peduncle are both afferent and efferent. The afferent fibres arise in the pons from the cells of the nucleus pontis of the opposite side, and terminate in arborizations around the cells of the cerebellar cortex. The efferent fibres arise from the cells of the cerebellar cortex of the same side, and terminate in arborizations around the cells of the nucleus pontis, mostly on the opposite side.

The inferior peduncles are principally composed of afferent fibres, which are derived chiefly from the dorsal (or direct) cerebellar tract and the olivo-cerebellar tract of either side. The fibres of the dorsal cerebellar tract terminate in the cortex of the superior vermis on both sides of the median line. The fibres of the olivo-cerebellar tract , which are derived from the inferior olivary nucleus of the medulla oblongata on the opposite side, terminate in the cortex of the vermis and cerebellar hemisphere. The superficial arcuate fibres, which form part of the inferior peduncle, are connected with the cortex of the vermis and cerebellar hemisphere. There are also fibres connecting the vermis with the vestibular nerve, thus forming the direct sensory cerebellar tract (see p. 1623).

It should be noted that the inferior peduncle comes up from below to a position between the other two, the middle peduncle being external and the superior internal. Having reached this position, the inferior peduncle suddenly bends backwards and passes into the cerebellum.

White and Grey Matter of the Cerebellum.—In the hemispheres and vermis the white matter is situated in the centre as the medulla, and the grey matter is disposed superficially as the cortex. The white matter in the interior of the vermis is occasionally termed the corpus trapezoides. When sagittal sections of a hemisphere are made, the mass of white matter in the centre is seen to send offshoots into the lobules. From the sides of these offshoots secondary processes are given off, and these in turn furnish tertiary processes, the white


THE NERVOUS SYSTEM


1485

latter in all cases being covered by grey matter. When the section 5 made across the direction of the laminae or folia the appearance •resented is like the trunk and branches of a tree; hence the name rbor vitce cerebelli is applied to it (see Fig. 902).

Nuclei.—The corpus dentatum (Fig. 902) is a collection of grey latter which is situated within the white matter of each hemisphere, nd is very like the inferior olivary nucleus in the olivary body of the aedulla oblongata. It is composed if a wavy grey lamina, disposed n the form of a capsule, which ncloses white matter. The capsule >resents an opening or hilum at its ipper and inner part, and through his a large number of the fibres >f the superior cerebellar peduncle merge from the interior.

There are three other nuclei on

ach side as follows
(1) the nucleus

imboliformis, close to the inner

ide of the hilum of the corpus

lentatum; (2) the nucleus globosus, nternal to the preceding ; and 3) the nucleus fastigii, or rooflucleus, situated in the vermis, dose to the median line, and contiguous to its fellow of the opposite dde.

Commissural and Association Fibres.—The commissural fibres pass

horn the white matter of one hemisphere to that of the opposite hemisphere. They traverse the vermis in two sets, superior and inferior. Die association fibres are confined to each side, and they connect idjacent laminae, passing across the bottom of the fissures which separate them.

Medullary Vela.—These are thin laminae or curtains of white matter, and are two in number, superior and inferior.

The superior medullary velum (or valve of Vieussens) is continuous with the white matter of the vermis. It extends between the converging superior cerebellar peduncles, bridging over the interval between them, and becoming continuous with their inner margins. Superiorly it extends to the inferior pair of quadrigeminal bodies, and inferiorly it passes into the corpus trapezoides or white matter of the vermis. It forms a large portion of the roof of the upper part of the fourth ventricle, and its dorsal surface supports the lingula of the superior vermis. From the upper part of the superior medullary velum a band of white fibres, called the frenulum veil, passes to the lower part of the median longitudinal groove which separates the lateral pairs of quadrigeminal bodies. Immediately below the inferior pair of quadrigeminal bodies the fourth pair of cranial nerves emerge from the superior medullary velum on either side of the frenulum veli. The


Fig. 902.—Anteroposterior Section through Lateral Lobe, showing Dentate Nucleus.


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A MANUAL OF ANATOMY


tract of Gowers (ventral spino-cerebellar tract), after having traversed the formatio reticularis of the medulla oblongata and the dorsal part of the pons, passes into the superior medullary velum, and then descends in the superior cerebellar peduncle to the cerebellum.

The inferior or posterior medullary velum is a thin lamina of white matter which consists of three parts—median and two lateral, right and left.

The median part supports dorsally the nodule of the inferior vermis. It is a prolongation of the white matter of the vermis, and lies on the upper or ventral aspect of the nodule, to which it is adherent. As it leaves the white matter it is contiguous to the superior medullary velum, but the two laminae take different directions. As they diverge they make the cerebellar recess or apex of the roof of the fourth ventricle.


Layer of Purkinje's Cells


Fia Mater


_ Molecular Layer


Granular Layer


White Medullary Substance


Fig. 903. —Structure of a Lamina ■the Cerebellum (magnified).


of


The superior medullary velum passes upwards between the dorsal parts of the superior peduncles of the cerebellum. The median part of the inferior medullary velum passes ventralwards and then downwards. It is succeeded in a downward direction by the ependymal epithelium and pia mater (tela chorioidea inferior), which form a large portion of the lower part of the roof of the fourth ventricle. The middle part of the inferior medullary velum forms the upper portion of


the lower part of the roof of the fourth ventricle.

Each lateral part of the inferior medullary velum extends laterally to the corresponding flocculus in the form of a semilunar band. The ventral surface of this band is directed towards the fourth ventricle, and the dorsal surface is related to the amygdala or tonsil. One border of the band is free and concave, whilst the other is continuous with the white matter of the corresponding cerebellar hemisphere.

The inferior medullary velum forms a part of the lobns noduli, the other parts being the nodule and the two flocculi.


Minute Structure of the Cerebellar Laminae. —Each lamina or folium of the cerebellum consists of (1) a central part or core of white matter, which is an offshoot from the white medullary substance; and (2) an external part or cortex of grey matter.

Grey Cortex. —The grey cortex is composed of two layers, an outer molecular layer and an inner granular layer. Between these two layers there is a stratum of characteristic large cells, called the cells or corpuscles of Purkinje.

The cells of Purkinje are pyriform or flask-shaped, and are situated, as just stated, between the molecular and granular layers. The narrow or superficial end of each cell projects into the molecular layer, and the broad or deep end rests








THE NERVOUS SYSTEM


1487


1 the granular layer. From the broad or deep end of each cell a single axon isses off, which enters the granular layer, where it soon becomes medullated, id then forms a nerve-fibre of the white medullary substance. The axon of urkinje’s cell gives off a few collateral recurrent branches, some of which end 1 the granular layer, whilst others enter the molecular layer.

From the narrow or superficial end of each cell one or two dendrons are given ff. These divide and subdivide at frequent intervals in the molecular layer like the antlers of a deer.' The dendritic processes so formed are arranged 1 an arborescent manner, and are distinct from those of adjacent cells. They ermeate the molecular layer as far as the surface.

The molecular layer consists of a few nerve-cells and many nerve-fibres.

The nerve-cells are situated partly in the inner or deep portion of the lolecular layer, and partly in its outer portion.

The inner cells are known as the basket-cells, and they lie in the vicinity of tie cells of Purkinje. Each basket-cell has several dendritic processes which imify in all directions. In addition to these processes there is an axon, which prings from the side of the cell and takes a transverse course. It gives off a umber of collaterals which pass towards the bodies of the cells of Purkinje. 'hese collaterals terminate by ramifying very freely around the cells of Purkinje s well as around the axons of these cells for a short distance. The minute srminal ramifications form a close basket-work, which encloses the ceil of hirkinje and its axon for a short distance.

The outer cells of the molecular layer are small, and each has several denritic processes and an axon. Each axon springs from the side of the cell, nd, taking a transverse course, it ends in numerous ramifications.

The fibres of the molecular layer are derived from the following sources: 1) The dendritic processes, and the recurrent collaterals of the axons of the ells of Purkinje; (2) the dendritic processes and axons of the outer cells; (3) the .endritic processes of the inner or basket cells; (4) the axons of the granule-cells >f the granular layer; (5) the fibres of Bergmann, which represent the processes I glia-cells in the granular layer; (6) the dendrons of the cells of Golgi; and 7) some fibres from the white medullary substance of the lamina.

The granular layer consists of (1) nerve- and glia-cells, and (2) fibres.

The nerve-cells are of two kinds—namely, granule-cells and cells of Golgi.

The granule-cells are small and very numerous. They are closely packed ogether, and impart to this layer a granular appearance. Each has several [endrons and one axon. The dendrons soon ramify, and the dendritic processes erminate in minute clusters within the granular layer, which are closely related o the granule-cells. The axon of each granule-cell passes into the molecular ayer, where it ramifies, its branches diverging and being closely related to the [endritic processes of the cells of Purkinje.

The cells of Golgi lie near the cells of Purkinje, and are larger than the granuleells. They are stellate, and each has several dendrons and an axon. The lendrons enter the molecular layer, in which they ramify. The axon ramifies r ery freely in the granular layer. The cells of Golgi may be regarded as associaion cells.

The glia-cells are situated close to the cells of Purkinje, and lie between the mter granule-cells. The superficial processes enter the molecular layer, and onstitute the fibres of Bergmann, which pass as far as the pia-matral covering if the lamina. Their deep processes pass between the granule-cells of the

ranular layer, and some of them enter the white medullary substance.

The fibres of the granular layer are derived from the following sources: 1) The axons of the cells of Purkinje; (2) the moss-fibres of Cajal; (3) the denIritic processes of the granule-cells; (4) the ramifications of the axons of the

ells of Golgi; (5) some of the deep processes of the glia-cells; and (6) some fibres

rom the white medullary substance.

White Matter.—The white matter of a cerebellai lamina is an >ffshoot of the principal white medullary substance, and composed


A MANUAL OF ANATOMY


1488

of nerve-fibres. (1) Some of these are the axons of the cells of Purkinje, and these enter the white matter. (2) Others pass through the granular layer into the molecular layer, where they divide into branches which are closely related to the more deeply placed dendritic processes of the cells of Purkinje. (3) A third set terminate in the granular layer, where they divide into branches which present moss-like swellings, furnished with short delicate filaments. These fibres are known as the moss-fibres of Cajal.

Development of the Cerebellum. —The cerebellum is developed from the dorsal laminae of the metencephalon, where this forms the front limb of the pontine flexure. In its growth it extends into the roof-plate.


4. The Fourth Ventricle.


The fourth ventricle (ventriculus quartus) is situated behind (1) the upper or open half of the medulla oblongata or bulb, and (2) the pons. It has two walls—ventral and dorsal.

Ventral or Anterior Wall.—This wall is usually referred to as the floor. It is formed by (1) the dorsal surface of the upper or open

half of the bulb, and


Fig. 904.— Diagram to show the Composition of Floor and Roof of Fourth Ventricle.


SMV, IMV, upper and lower medullary vela.


(2) the dorsal surface of the pons between the converging superior peduncles of the cerebellum. In shape it is rhomboidal, the bulbar and pontine parts being triangular and having their bases applied to each other. The floor is sometimes spoken of as the fossa rhomboidea (see Fig. 892).

The lower end is tapering, and lies between the clavae of the funiculi graciles. In this situation the cavity of the ventricle is continuous with the central canal of the spinal cord after that canal has


traversed the lower or closed half of the bulb. The upper end is somewhat tapering, and lies between the converging superior peduncles of the cerebellum. In this situation the cavity of the ventricle is continued into the aqueduct (of Sylvius), which traverses the mesencephalon and opens superiorly into the third ventricle.

The floor is widest across its centre, which is on a level with the upper ends of the ' restiform bodies ’ of the bulb. The cavity of the ventricle is here prolonged on either side round the outer aspect




THE NERVOUS SYSTEM 1489

[ the corresponding restiform body towards the olive. This probation is known as the lateral recess.

An opening in the lateral part of this recess, involving the wering pia mater and opening into the subarachnoid space, is known 5 the lateral aperture of the fourth ventricle.

The floor is covered by a thick layer of grey matter, which is mtinuous with the central grey matter of the lower or closed half [ the bulb. This grey matter is covered by ependyma, the epithelial ills being continuous with those which line the central canal of the unal cord.

The floor is traversed in the median line by a slight longitudinal roove, which divides it into two symmetrical longitudinal halves.


Fig. 905.—Dorsal View of Mid- and Hind-Brains with Thalamus

(Cerebellum Removed) .

iach half is crossed at its widest part by bundles of white fibres, ailed auditory stricB. They wind round the upper part of the restiorm body, and pass transversely across the corresponding half of he floor as far as the median longitudinal groove, into which they ink. They belong to the cochlear division of the auditory nerve, in onnection with which they will be described.

The floor is divided into two parts, lower and upper, by the striae

if either side.

Lower or Bulbar Part.— The bulbar part is formed by the dorsal urface of the upper or open part of the bulb. It is bounded on either ide by fi) the clava of the funiculus gracilis, (2) the cuneate tubercle if the funiculus cuneatus, and (3) the restiform body, in this order

94






1490


A MANUAL OF ANATOMY


from below upwards. The lower end constitutes, as stated, a tapering point which carries a small ridge of grey matter, the obex, at its extremity. The bulbar part is traversed in the median line by a longitudinal groove, already referred to, and this groove subdivides it into twc symmetrical halves.

Immediately below the auditory striae on either side, and not far from the median longitudinal groove, there is a small triangular depression, known as the fovea inferior. Its apex extends to the striae and the lateral angles of its base are prolonged downwards as two grooves—inner and outer. The inner groove passes in a somewhat curved manner towards the point of the lower end, and the outer groove passes downwards and outwards towards the lateral boundary.


Between these two diverging grooves there is a triangular area, called the vagal triangle. Its apex is at the fovea inferior, and its base is directed downwards and outwards. It has a dark colour, and from this circumstance it is known as the ala cinerea. Deep to it there is the dorsal nucleus of the vagus and glosso-pharyngeal nerves (Fig 905).

A second triangular area, called the hypoglossal triangle, is situated between the median longitudinal groove and the medial of the two grooves prolonged from the angles of the base of the fovea inferior. Its base is directed upwards towards the striae, and its apex downwards towards the lower point. The area is slightly elevated, and is associated with the lower part of the eminentia medialis. Subjacent to this area is the upper part of the nucleus of the hypoglossal nerve.










THE NERVOUS SYSTEM 1491

A third triangular area, called the vestibular area or triangle, is ituated between the lateral boundary of the floor and the outer of he two grooves prolonged from the angles of the base of the fovea iferior. Its base, like that of the hypoglossal triangle, is directed pwards, and is continued into an eminence, over which the auditory triae pass. This eminence is known as the vestibular area or tubercle, ubjacent to the vestibular area and tubercle there is the dorsal or hief terminal nucleus of the vestibular division of the eighth nerve.

Upper or Pontine Part.—The pontine part of the floor is formed y the dorsal surface of the pons between the converging superior •eduncles of the cerebellum, which constitute its lateral boundaries, ts upper somewhat tapering end adjoins the lower end of the aqueduct, ike the bulbar part, it is traversed in the median line by a longiudinal groove, already referred to, which subdivides it into two ymmetrical halves.

Above the auditory striae, and in line with the fovea inferior, here is a slight depression, called the fovea superior, the two foveae >eing separated from each other by the vestibular tubercle. Between he fovea superior and the median longitudinal groove there is a ^ell-marked prominence, called the eminentia medialis. Deep to his eminence immediately above the striae acusticae, is the ibducent nucleus, or nucleus of the sixth cranial nerve, and the minentia medialis is really formed by fibres of the seventh nerve curvound the dorsal surface of the sixth nucleus just deep to the floor )f the ventricle. For this reason an alternative name for the eminence s the colliculus facialis. The eminence is continued downwards nto the trigonum hypoglossi, and superiorly it extends towards the ower end of the aqueduct of the mid-brain. Extending upwards rom the fovea superior towards the region of the lower end of the iqueduct there is a slight depression, known as the locus cseruleus, vhich has a dark grey or somewhat blue colour. This colour is due

o a subjacent group of deeply pigmented nerve-cells, known as the

substantia ferruginea. This group may belong to the chief motor lucleus of the fifth cranial nerve, or it may be a terminal nucleus for some of the sensory fibres of that nerve.

Dorsal or Posterior Wall of Fourth Ventricle.— this wall is usually eferred to as the roof, and it is divisible into two parts—upper and ower.

The upper part is formed chiefly by the superior or anterior medulary velum, which extends between the inner margins of the dorsal ispects of the superior peduncles of the cerebellum. It is also formed

o a certain extent by these peduncles as they converge and slightly

overhang the angular space between them. I he lower part of the roof s formed, from above downwards, by (1) the inferior or posterior nedullary velum, and (2) the ependymal epithelium of the ventiicle, covered by pia mater. The inferior medullary velum is separated from

he superior velum by the recess (Fig. 9 ° 4 )> within which the cerebellum

ictually forms a part of the roof; the inferior velum terminates in a free


1492


A MANUAL OF ANATOMY


margin. Beyond this free margin there is the ependymal epitheliun of the ventricle, covered, as stated, by pia mater. This portion o pia mater is called the tela chorioidea inferior.

The epithelial part of the roof presents superficially threi laminae of white nervous matter—namely, the obex and thi ligulae. The obex is a thin triangular lamina which is situatec at the lower point of the ventricle, being attached laterally t( the diverging clavae. The ligulce are right and left. Each is c narrow band, which is continuous interiorly with the obex It is attached inferiorly to the clava and the cuneate tubercle It then passes transversely outwards over the dorsal aspect of the restiform body. The transverse part of the ligula forms the lowei boundary of the lateral recess of the ventricle.


Fig. 907. —The Fourth Ventricle and Right Hemisphere of the Cerebellum (in Section) (Hirschfeld and Leveille).


In the lower part of the roof of the fourth ventricle, below the lower limit of the inferior medullary velum, there is a perforation through the pia mater and ependyma, known as the foramen of Magendie. This, situated in the mid-line, forms an opening between the fourth ventricle and the subarachnoid space, and with the lateral recesses allows the cerebro-spinal fluid to pass from the interior to the surface of the brain. Its modern name is median aperture of fourth ventricle.

Choroid Plexuses of Fourth Ventricle.—These are two in number,

right and left. Each is a longitudinal inflexion of the pia mater which forms the tela chorioidea inferior, and it invaginates the ependymal epithelium of the lower part of the roof of the ventricle, by which it is covered on its ventricular surface. Each choroid plexus consists of two parts—longitudinal and transverse—and the two plexuses are disposed thus: ] |". The longitudinal parts lie on either






THE NERVOUS SYSTEM


1493


ide of the median line, and extend upwards from the region of the oramen of Magendie. Each transverse part extends outwards into he corresponding lateral recess of the ventricle

Development of Fourth Ventricle.—The lower or bulbar part is developed from the myelencephalon, and the upper or pontine part is developed from the metencephalon, these being the two divisions of the rhombencephalon. The cavity is the cavity of the neural tube, dilated and made diamond-shaped as a result of the formation of the pontine flexure (p. 57).


TELENCEPHALON.

Cerebral Hemispheres.

The cerebral hemispheres are right and left. Each is semi-ovoid, md presents two extremities and three surfaces.

The extremities are anterior and posterior. The anterior is thick md round, and its most projecting part is called the frontal pole, rhe posterior extremity is narrow and pointed, and its most projecting Dart is called the occipital pole. The surfaces are lateral, medial, and inferior. The medial surface is convex, in adaptation to the concavity Df the cranial vault. The lateral surface is flat and vertical, and it forms the lateral boundary of the great longitudinal fissure. For the most part it is in contact with the falx cerebri. The inferior surface is irregular, being adapted to the corresponding lateral divisions of the anterior and middle fossae of the interior of the base of the skull and the upper surface of the tentorium cerebelli. It is crossed transversely by a deep cleft, representing the stem of the lateral fissure.. The portion in front of this fissure is known as the orbital area, and is concave, in adaptation to the convexity of the orbital plate of the frontal bone, upon which it rests. The extensive portion behind the stem of the lateral fissure is known as the tentorial area, and is prominent and arched. Its anterior portion is received into the lateral division of the middle cranial fossa, and its posterior portion rests upon the tentorium cerebelli.

The borders of each hemisphere are four—supero-medial, mferolateral, superciliary, and internal occipital. The supero-medial border separates the lateral from the medial surface. The infero-lateral border separates the lateral surface from the tentorial area of the inferior surface. The superciliary border separates the front part of the lateral surface from the orbital area of the inferior surface. The internal occipital border separates the medial surface from the tentorial area of the inferior surface, and it extends from the occipital pole to the splenium of the corpus callosum.

The exterior of each hemisphere is broken up into tortuous eminences, called gyri or convolutions, and these are separated from each other by clefts, called sulci or fissures. The exterior is composed of grey matter,


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which is spoken of as the cerebral cortex, and the interior is occupied by white matter, which forms the medullary centre. The breaking up of the hemispheres into gyri, with the intervening sulci, greatly increases the amount of cerebral cortex, and to a proportionate extent of pia mater.

It is sometimes the practice to distinguish between fissures and sulci of the brain, though many regard it as a refinement. If it is necessary, the fissures may be defined as clefts which either pass from one surface of the brain to another or, if they do not do that, cause an elevation in the wall of the lateral


biG. 908.— Views of Brain, not showing Convolutions. A, from above; B, from left; C, from below; D, from behind.


ventricle. The difficulty is that, with this definition, the same depression is sometimes a fissure and sometimes a sulcus.

Subject to this explanation, the following clefts would rank as fissures and them claims will be dealt with as they are described: (1) Lateral, (2) central, .( 4 ) hippocampal, (5) calcarine, (6) collateral, (7) parieto-occipital. ^Mwessions which do not fulfil these requirements merely rank as sulci.

the fissures thus defined are deeper and more constant in arrangement than the sulci. 0

Each hemisphere presents six principal clefts, called interlobar, and by means of these it is divided into six lobes.





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Interlobular Clefts.

1. Lateral fissure [Sylvian). 4. Cingulate sulcus.

2. Central fissure [Rolando). 5. Collateral fissure.

3. Parieto-occipital fissure. 6. Circular or limiting sulcus.

Interlobular Fissures.—The lateral fissure (O.T., fissure of Sylvius), which is the first fissure to appear in the course of development, begins on the inferior surface of the hemisphere at the anterior perforated substance in a depression, called the vallecula cerebri (or Sylvii). From this point it passes horizontally outwards to the external surface of the hemisphere, where it divides into three diverging branches. It is a deep cleft, which is overhung posteriorly by the front part of the temporal lobe, and it separates the orbital surface of the frontal from



Fig. 909.—Lateral View of Left Hemisphere.

In this specimen the horizontal (AH) and ascending (AV) anterior rami arise separately from lateral fissure. The pars triangularis lies between them.

the temporal lobe. The posterior border of the small wing of the sphenoid bone faces the fissure, which lodges the middle cerebral artery. The limbs into which the fissure divides are anterior horizontal, ascending, and posterior horizontal. The anterior horizontal limb passes forwards into the frontal lobe, its length being about f inch. The ascending limb passes upwards and slightly forwards into the frontal lobe for about 1 inch, but its length is variable. The posterior horizontal limb is the longest and most conspicuous. It passes backwards on the external surface of the hemisphere for at least 2 inches, having poi tions of the frontal and parietal lobes above it, and the temporal lobe below it. Finally, it turns upwards into the parietal lobe for a very short

distance

The central fissure (see Fig. 909), also known as the central sulcus and fissure of Rolando , begins at the supero-medial border of the hemi

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sphere a little behind its mid-point, and ends above the centre of the posterior horizontal limb of the lateral fissure. It does not usually open into this limb, but may do so. Superiorly the fissure in most cases intersects the supero-medial border to reach the medial surface of the hemisphere, upon which it passes backwards for a very short distance. The direction of the fissure is irregularly downwards and forwards over the external surface of the hemisphere, and it separates the frontal from the parietal lobe. It describes two bends. The upper genu has its concavity directed forwards, and is situated about the junction of the upper and middle thirds of the fissure. The lower genu has its concavity directed backwards, and is situated on a more anterior plane than the upper genu. Below the lower genu the direction of the fissure is almost vertical, with a slight inclination backwards. The fissure is sometimes interrupted.


Central Sulcus


Medial Frontal Gyrus


Cingulate Gyrus

Callos. Sulcus •


--- Paracentral Lobule


Cingulate

Sulcus

Suprasplenial Fissure Parieto-occ.

Fissure Cuneus


Calcarine

Fissure


Uncus


Rhinal Sulcus


, Lingual Gyrus

Collateral Fissure

\\ Occipito-Temp. Gyrus ' Hippocampal Gyrus Inf. Temp. Gyrus


Fig. 910.—Medial Aspect of Right Hemisphere. Approximate position of lateral ventricle marked in blue.


The parieto-occipital fissure is situated about 2 inches behind the upper end of the central fissure, and separates the parietal from the occipital lobe. It is composed of two limbs, external and internal, which are continuous with each other at the supero-medial border of the hemisphere, where they form a right hngle. The external limb is situated on the lateral surface of the hemisphere, upon which it passes transversely outwards for about £ inch, when it is arrested by the convolution which connects the parietal and occipital lobes. The internal limb appears as a deep, almost vertical cleft on the medial surface of the hemisphere, which opens into the calcarine fissure a short distance behind the splenium of the corpus callosum (see Figs. 910 and 917).

The cingulate sulcus is situated on the medial surface of the hemisphere. It commences below the rostrum of the corpus callosum,


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near the anterior perforated area, and, bending round the genu, it passes backwards above the corpus callosum, from which it is separated by the cingulate gyrus. At a point a little behind the centre of the internal surface of the hemisphere it turns upwards, and terminates at the supero-medial border a short distance behind the upper end of the central fissure. The cingulate fissure lies between the frontal and limbic lobes, the medial frontal gyrus being above it and the cingulate gyrus below it (see Fig. 910).

The collateral fissure is situated on the inferior or tentorial surface of the hemisphere. It starts near the occipital pole, and extends forwards towards the temporal pole. Posteriorly it has the calcarine fissure above, and in line with it, and anteriorly the hippocampal gyrus holds this position on its medial side. It separates the temporal lobe from the hippocampal portion of the limbic lobe. The middle portion of the collateral fissure gives rise to the eminentia collateralis in the floor of the lateral ventricle.

The circular or limiting sulcus is situated deeply in the anterior part of the posterior horizontal limb of the lateral fissure. It almost surrounds the convolutions which constitute the insula, and is composed of three parts-—superior, inferior, and anterior. The superior part separates the insula from the frontal and parietal lobes, the inferior part separates it from the temporal lobe, and the anterior part separates it from the frontal lobe. The circular fissure is deficient in the region of the apex of the insula (see Fig. 920).

Lobes of the Cerebral Hemisphere—Frontal Lobe.—This is of large size. On the external surface of the hemisphere it is bounded behind by the central fissure and below by the posterior horizontal limb of the lateral fissure. On the inferior surface it is bounded behind by the stem of this fissure. On the internal surface it is bounded by the cingulate fissure. The frontal lobe has three surfaces—lateral, inferior, and medial.

Lateral Surface.—This surface presents three principal sulci—precentral, superior frontal, and inferior frontal.

The precentral sulcus is more or less parallel to the central fissure, the ascending frontal or precentral gyrus intervening between the two. It may be a single cleft, but it more frequently consists of two parts, superior and inferior. The superior part is usually joined above by the superior frontal sulcus. The inferior part passes superiorly into the middle frontal gyrus for a short distance in a forward and upward direction (see Fig. 909).

The superior and inferior frontal sulci extend forwards from the precentral sulcus.

The gyri of the external surface are as follows: precentral or ascendingfrontal, superior frontal, middle frontal, and inferior frontal (see Fig. 909) The ascending frontal or precentral gyrus (Fig. 909, A) is bounded behind by the central sulcus, and in front by the superior and inferior parts of the precentral sulcus. It extends from the supero-medial border of the hemisphere to a little behind the Sylvian point, which


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corresponds to the place where the stem of the lateral fissure appears on the external surface of the hemisphere, and divides into its three branches. Below the lower end of the central fissure it is, as a rule, connected with the ascending parietal or postcentral gyrus by an annectant gyrus.

The superior or first , middle or second, and inferior or third frontal gyri

(C, D, E) are arranged in tiers, which are disposed antero-posteriorly, but the first and second often are subdivided, so as to make five tiers in

all. They are separated from the ascending frontal or precentral gyrus by the superior and inferior parts of the precentral sulcus.

The superior frontal gyrus is narrow, and lies between the supero-medial border of the hemisphere and the superior frontal sulcus. It is continuous with the medial frontal gyrus on the medial surface of the hemisphere, and is partially broken up into two parts, upper and lower.

The middle frontal gyrus, which is broad, is usually connected with the ascending frontal or precentral gyrus by an annectant gyrus. It is broken up anteriorly into two parts, upper and lower, by an anteroposterior secondary sulcus; and it is cut into behind by the upper portion of the inferior part of the precentral sulcus.

The inferior frontal gyrus lies below the inferior frontal sulcus, and in front of the lower part of the precentral sulcus. The anterior horizontal and the ascending limbs of the lateral fissure enter it and subdivide it into three parts—namely, pars orbitalis, pars triangularis, and pars basilaris, or, better still, orbital, frontal, and fronto-parietal opercala. The orbital operculum lies below the anterior horizontal limb of the lateral fissure; the frontal operculum is situated between the anterior horizontal and the ascending limbs of the fissure; and the fronto-parietal operculum is placed between the ascending limb of the fissure and lower part of the precentral sulcus. The inferior frontal gyrus is connected posteriorly with the lower end of the ascending frontal or precentral gyrus by an annectant gyrus.

Inferior or Orbital Surface of the Frontal Lobe.—This surface presents two sulci, olfactory and orbital (see Fig. 914).

The olfactory sulcus is parallel to the medial border, from which it is separated by the gyrus rectus. It lodges the olfactory tract and olfactory bulb. The orbital sulcus is of very variable form, but, as a rule, bears some resemblance to the letter )-(. It has, therefore, three limbs


Fig. 911.—The Left Cerebral Hemisphere (Superior Surface).

Red=frontal lobe. Orange=parietal lobe. Blue=occipital lobe.







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—medial, lateral, and transverse. The medial limb is separated from the olfactory sulcus by the medial orbital gyrus. The lateral limb is curved, and has external to it the orbital part of the inferior frontal gyrus. The transverse limb passes in a more or less curved manner between the other limbs.

The gyri of the orbital surface are: gyrus rectus, medial orbital gyrus, anterior orbital gyrus, lateral orbital gyrus, and posterior orbital gyrus.

The gyrus rectus lies between the olfactory sulcus and the medial border. The medial orbital gyrus is placed between the olfactory sulcus and the inner limb of the orbital sulcus. The lateral orbital gyrus is external to the other limb of the orbital sulcus. The anterior orbital gyrus is situated in front of the transverse limb of the orbital sulcus. The posterior orbital gyrus lies behind the transverse limb of the orbital sulcus.


Fig. 912.—The Right Cerebral and Cerebellar Hemispheres (Lateral

Surface).

Red=frontal lobe. Blue=occipital lobe.

Orange—parietal lobe. Green=temporal lobe.

Purple=cerebellar hemisphere.

Medial Surface of the Frontal Lobe.— The medial surface presents only one convolution, the medial frontal or marginal gyrus, which is situated between the supero-medial border of the hemisphere and the cingulate sulcus. It is continuous with the superior frontal gyrus, and anteriorly is broken up by one or two sulci. Its posterior part is almost completely detached, and forms the paracentral lobule, so named because it contains the upper end of the central fissure (Fig. 910).

Parietal Lobe.— This lobe lies between the large frontal and small occipital lobes, and above the temporal lobe. It is bounded anteriorly by the central fissure, which separates it from the frontal lobe. Posteriorly it is bounded by (1) the external parieto-occipital fissure, and (2) a line drawn across the external surface of the hemisphere from the extremity of this fissure towards the pre-occipital notch. on the inferolateral border of the hemisphere, from i-| to 2 inches in fiont of the occipital pole.


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A MANUAL OF ANATOMY


The parietal lobe has two surfaces—lateral and medial.

Lateral Surface.—This surface presents the following sulci: the intraparietal sulcus, composed of four parts; and the terminal portions of [a) the posterior limb of the lateral fissure, ( b ) the first temporal or parallel sulcus, and (c) the second temporal sulcus.

The inferior and superior postcentral sulci may be distinct, or continuous with each other. They lie behind the central fissure, with which they are parallel, and from which they are separated by the ascending parietal or postcentral gyrus (Fig. 909, B).


Cerebral Hemisphere


OccipitaL

Poie


_Frontal

Pole


Pons

—Medulla Oblongata


Fig. 913.— The Encephalon (Right Lateral View) (Hirschfeld

and Leveille).


1. Central Fissure

2. Posterior Horizontal Limb of Lateral Fissure

3. Ascending Limb of Fissure

4. Anterior Horizontal Limb of Fissure 5,5. Intraparietal Sulcus

6. Ramus Horizontalis


7. Ramus Occipitalis

8. Transverse Occipital Sulcus

9. Lateral Occipital Sulcus

10. External Occipito-parietal Fissure

11. Superior Temporal, or Parallel, Sulcus

12. Inferior Temporal Sulcus


The intraparietal sulcus is often in two parts, horizontal and occipital (see Fig. 913).

The ramus horizontalis passes backwards and slightly upwards from the upper end of the inferior postcentral sulcus. It has the superior parietal lobule above it, and the inferior parietal lobule below it.

The ramus occipitalis is usually continuous with the last branch, and passes back into the occipital lobe as the lower boundary of the arcus parieto-occipitalis.






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The terminal portions of (a) the posterior horizontal limb of the lateral fissure, (b) the first temporal or parallel sulcus, and (c) the second temporal sulcus, are confined to the lower part of the external surface of the parietal lobe, where they lie in the order named from before backwards.

The gyri of the lateral surface are as follows: ascending parietal; superior parietal; and inferior parietal, with its supramarginal, angular, and postparietal gyri.

The ascending parietal or postcentral gyrus is situated immediately behind the central fissure, which separates it from the ascending frontal or precentral gyrus in front of that fissure. Posteriorly it is limited by the superior and inferior postcentral sulci. It extends from the supero-medial border of the hemisphere to the posterior horizontal limb of the lateral fissure, and it lies parallel to the ascending frontal or precentral gyrus, with which it is connected below the central fissure.

These two gyri, from their relation to the central fissure, are often spoken of by neurologists as the ‘ central gyri,’ though the name, if not clearly understood, is apt to lead to confusion with the gyri of the central lobe or insula.

The superior parietal lobule is situated between the ramus horizontalis and the supero-medial border of the hemisphere, where it is continuous with the quadrate lobule, or precuneus, of the internal surface. Anteriorly it is limited by the superior postcentral sulcus, round the upper end of which it is continuous with the postcentral gyrus. Posteriorly it is bounded by the external part of the parieto-occipital fissure, round the extremity of which it is connected with the occipital lobe by the arcus parieto


Fig. 914. —The Inferior Surface of the Left Cerebral Hemisphere, showing the Gyri and Sulci.


occipitalis.

The inferior parietal lobule is situated behind the inferior postcentral sulcus, and below the ramus horizontalis and ramus occipitalis. It is broken up into several gyri, three of which the supramarginal, angular, and postparietal—lie in this order from before backwaids. The supramarginal gyyus arches over the ascending extremity of the posterior limb of the lateral fissure. The angular gyrus arches over the







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A MANUAL OF ANATOMY


ascending extremity of the first temporal or parallel sulcus, and is continuous with the second temporal gyrus. The postparietal gyrus arches round the ascending extremity of the second temporal sulcus, and is continuous with the third temporal gyrus. These three subdivisions of the inferior lobule are sometimes described simpfy as anterior, middle, and posterior parts.

Medial Surface of the Parietal Lobe.—The medial surface is of quadrilateral outline, and constitutes the quadrate lobule or precuneus. It is bounded in front by the upturned posterior extremity of the cingulate sulcus, behind by the internal parieto-occipital fissure, and below by the suprasplenial sulcus and a portion of the gyrus cinguli (Fig. 916).


Corpus Callosum


Pineal Body Splenium


Anterior Pillar of Fornix Septum Lucidum


Genu passing into Rostrum


Corpora Quadri- g gemina


Anterior Commissure Optic Thai, and Connexus Thalamus Nerve Pituitary Body Tuber Cinereum Corpus Mamillare


Cerebellum


Fourth Ventricl


Third Nerve

1 1 Pons

i Crus Cerebri Aqueduct

Medulla Oblongata


fG. 915 .—The Medial Surface of the Left Cerebral Hemisphere

(Hirschfeld and Leveille).


Occipital Lobe.—This lobe lies behind the parietal and temporal lobes, and forms the posterior part of the cerebral hemisphere.

Laterally the lobe is bounded in front by the external parietooccipital fissure, and a line connecting this fissure with the pre-occipital notch on the infero-lateral border of the hemisphere. Medially it is bounded in front by the internal parieto-occipital fissure, which separates it from the quadrate lobule, or precuneus, of the parietal lobe. Inferiorly it is continuous with the temporal and hippocampal regions, but the separation may be indicated by a line connecting the preoccipital notch with the portion of the hippocampal formations which lie below the splenium of the corpus callosum, this portion being known as the ‘ isthmus.’



THE NERVOUS SYSTEM


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The occipital lobe is pyramidal, having an apex and three surfaces— lateral, medial, and inferior.

The apex forms the occipital pole of the cerebral hemisphere.

Lateral Surface (see Fig. 913).—This surface presents two sulci, transverse occipital and lateral occipital. The transverse occipital sulcus is formed by the bifurcation of the posterior end of the ramus occipitalis of the intraparietal sulcus, and it crosses the upper part of the occipital lobe obliquely. Its upper limb lies a little behind the external part of the parieto-occipital fissure, from which it is separated by a portion of the arcus parieto-occipitalis, and its lower limb is behind the postparietal gyrus. The lateral occipital sulcus is situated on the external surface of the occipital lobe, and extends almost horizontally from behind forwards. It divides the external surface of the lobe into two parts, upper and lower, which are connected with the


Gyrus Dentatus

Fig. 916.—The Medial Surface of the Right Cerebral Hemisphere

(Hirschfeld and Leveille).

parietal and temporal lobes by annectant gyri. These sulci and gyri are very variable in appearance.

Medial Surface.—On the medial surface is the calcarine fissure.

This is a deep cleft which starts on the internal aspect of the occipital pole in a bifurcated manner. It takes a curved course forwards, passing at first upwards and then downwards, and ends by reaching the hippocampal gyrus beneath the splenium of the corpus callosum. It is joined at a point anterior to its centre by the internal parietooccipital fissure, and between the two fissures is the cuneus. The calcarine fissure is composed of two parts: precalcarine, representing the portion in front of the internal part of the parieto-occipital fissure; and postcalcarine, representing the portion behind that fissure. The precalcarine fissure gives rise to the calcar avis, on the inner wall of the posterior cornu of the lateral ventricle (Fig. 917) The gyri of the internal surface are two in number—namely, the

cuneus and the gyrus lingualis.





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A MANUAL OF ANATOMY


The cuneus is triangular, and is wedged in between the posterior calcarine fissure and the internal parieto-occipital fissure. The gyrus lingualis (infracalcarine gyrus) is situated between the calcarine fissure above and the posterior part of the collateral fissure below. Anteriorly it becomes narrow, and joins the hippocampal gyrus. The lower portion of this gyrus is visible on the inferior surface of the lobe.

Inferior Surface.—The inferior or tentorial surface presents the posterior part of the occipito-temporal gyrus, medial to which is the posterior part of the collateral fissure, and internal to this again there is the lower portion of the gyrus lingualis (see Fig. 918).

Temporal Lobe.—The temporal lobe (see Fig. 913) is prominent, and of large size. It is situated below the posterior horizontal limb of the lateral fissure, and behind the stem of that fissure. Superiorly it is bounded by the horizontal portion of the posterior limb of the


Fig. 917.—Medial Aspect of Parieto-occipital Region of Left Hemisphere, to show Internal Parietal Occipital Fissure, Anterior and Posterior Calcarine.

Visual area coloured.

fissure, and a line prolonging this limb backwards to meet the anterior boundary of the occipital lobe. Anteriorly it is bounded by the stem of the fissure, which separates it from the orbital area of the frontal lobe. Posteriorly it is continuous with the occipital lobe, but the separation may be indicated by the following lines: externally by a line connecting the extremity of the external parieto-occipital fissure with the pre-occipital notch, and below and medially by a line connecting the pre-occipital notch with the splenium of the corpus callosum. Its medial surface above is separated from the hippocampal gyrus by the collateral fissure. The temporal lobe is somewhat pyramidal, the rounded apex being directed forwards. The apical part forms the temporal pole, and underlies the stem of the lateral fissure. The uncus of the hippocampal gyrus lies on its inner side, but on a more posterior level, and separated from it by the temporal sulcus.


THE NERVOUS SYSTEM


1505


The lobe presents three surfaces—superior, lateral, and inferior.

The superior or opercular surface is concealed within the lateral fissure, and is directed towards the insula.

The lateral surface has two horizontal sulci and three convolutions, the latter being disposed one above the other.

The sulci are called first and second temporal. The first temporal sulcus is parallel to the posterior limb of the lateral fissure, from which

ircumstance it is called the parallel

sulcus. Starting near the temporal pole, it turns upwards posteriorly into the parietal lobe, where the angular ?yrus arches over it. The second temporal sulcus is parallel to the first, below which it lies, and it is usually broken up into two or more parts by annectant ^yri. Posteriorly it turns upwards into the parietal lobe, where the postparietal ^yrus curves round it.

The first temporal gyrus is situated uetween the posterior limb of the lateral ussure and the parallel sulcus. Posteriorly it is continuous with the infraparietal lobule. The second temporal ?yrus lies between the parallel and second temporal sulci. The third temporal gyrus lies below the second temporal sulcus, and posteriorly is con:inuous with the lower part of the ixternal surface of the occipital lobe.

On the inferior or tentorial surface )f the temporal lobe is the occipito:emporal sulcus and the occipito:emporal gyrus. The occipito-temporal iulcus extends from before backwards, ying near the infero-lateral margin of he hemisphere, and lateral to the colateral fissure (see Fig. 918). It is lsually broken up into parts by anlectant convolutions. The occipitotemporal gyrus is situated between the )ccipito-temporal sulcus and the collateral fissure, and extends from he occipital pole to the temporal pole. Lateral to the occipitoemporal sulcus there is the narrow inferior or tentorial surface of the hird temporal gyrus.

Insula (Island of Reil) (see Fig. 920).—This lobe is situated deeply vithin the lateral fissure, and is concealed from view by the opercular [yri, to be presently described. It is triangular, the apex being lirected downwards towards the vallecula cerebri and anterior per 95


Fig. 918.—The Inferior Surface of the Left Cerebral Hemisphere, showing the Gyri and Sulci.






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A MANUAL OF ANATOMY


forated area. The circular or limiting sulcus being here absent, the grey matter of the apex is continuous with that of the perforated area, this point being called the limen insulce. Elsewhere the island is surrounded by the circular or limiting sulcus, which has been already described. The insula presents several sulci, which diverge as the}/ pass from the apical region to the base, and these map it out into gyri. One of these sulci is known as the sulcus centralis insulae. It extends from the apex to the base in an upward and backward direction almost in line with the central fissure, and it divides the insula into two lobules, precentral and postcentral.

The precentral lobule is composed of three or four short gyri, called the gyri breves , which converge as they descend from the base, but they do not reach the apex or pole of the precentral lobule. The post


Fig. 919.—The Insula exposed by Removal of Opercula.

C, sulcus centralis insulae.


central lobule is formed by the gyrus longus, which is usually broken up into two gyri towards the base of the insula.

The direct internal or medial relation of the insula is the claustrum, internal to which there are, in succession, the external capsule, the nucleus lentiformis, the internal capsule, and the nucleus caudatus.

Opercula Insulae.—The parts of the cerebral hemisphere which bound the three limbs of the lateral fissure and overhang the insula are called; the opercula insulae. They are four in number—fronto-parietal, temporal, frontal, and orbital—and have been mentioned already (p. 1498).

Limbic Lobe.—This name was given in former times to a part of the brain, on its medial aspect, which included what is now known as the rhinencephalon, and also the cingulate gyrus.



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The interrelations of the various parts will be considered more appropriately under the h