Book - Buchanan's Manual of Anatomy including Embryology 5

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I have decided to take early retirement in September 2020. During the many years online I have received wonderful feedback from many readers, researchers and students interested in human embryology. I especially thank my research collaborators and contributors to the site. The good news is Embryology will remain online and I will continue my association with UNSW Australia. I look forward to updating and including the many exciting new discoveries in Embryology!

Frazer JE. Buchanan's Manual of Anatomy, including Embryology. (1937) 6th Edition. Bailliere, Tindall And Cox, London.

Buchanan's Manual of Anatomy: I. Terminology and Relative Positions | II. General Embryology | III. Osteology | IV. Bones of Trunk | V. Bones of Head | VI. Bones of Upper Limb | VII. Bones of Lower Limb | VIII. Joints | IX. The Upper Limb | X. Lower Limb | XI. The Abdomen | XII. The Thorax | XIII. Development of Vascular Systems | XIV. The Head and Neck | XV. The Nervous System | XVI. The Eye | XVII. The Ear | Glossary
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Chapter V The Bones of the Head

The head or skull is supported on the upper end of the vertebral column, and is divisible into the cranium and face. The cranium or brain-case is composed of eight bones—namely, the occipital, two parietals, frontal, two temporals, sphenoid, and ethmoid. The face, which protects organs of special sense, such as the eyes, the olfactory mucous membrane, and the tongue, and also supports the teeth, is composed of the following fourteen bones, the majority of which are arranged in pairs: the two maxillae, two zygomatics, two nasals, two lacrimals, two inferior nasal conchae, two palatine bones, the vomer, and the mandible. All the bones of the skull, except the mandible, are immovably united by sutures.


The Occipital Bone

The occipital bone is so named because it occupies the posterior and inferior parts of the cranium. It is lozenge-shaped and curved, its long axis extending from above downwards and forwards. At its lower and anterior part there is a large opening, called the foramen magnum, by which the cranial cavity communicates with the vertebral canal. The bone is divisible into four parts, which meet around this opening. The part behind is called the squama, that in front the basilar part, and the part at either side the condylar portion.

The squama presents two surfaces, three angles, and four borders. The posterior or external surface is convex and projected at its centre into the external occipital protuberance, from which a median ridge, called the median nuchal line, passes downwards and forwards to the foramen magnum. The protuberance and line give attachment to the ligamentum nuchse. Arching outwards on either side from the protuberance to the lateral angle there is the superior nuchal line, the convexity of which is directed upwards. The two lines with the protuberance divide this surface into an upper or interparietal and a lower or supra-occipital part. A little above each superior nuchal line there is the highest nuchal line, which has a bold curve with the convexity upwards, and gradually subsides in the superior nuchal line externally. Between these two lines there is a semilunar area, over which the bone .is smooth and dense. The highest nuchal line gives attachment to the epicranial aponeurosis medially, and to fibres of the occipitalis laterally. The superior nuchal line gives origin over about its inner third to the trapezius, and laterally to fibres of the occipitalis, whilst over its outer half, or more, it gives insertion to the sterno-mastoid, immediately below which the splenius capitis is inserted over about the outer third. The portion of this surface above the highest nuchal lines is smooth, convex, and covered by the epicranial aponeurosis. The portion below the superior nuchal lines, which is rough and irregular, is divided into two equal lateral parts by the median line, and each of these is subdivided into an upper and lower portion by the inferior nuchal line, which extends from the centre of the crest to the extremity of the jugular process. The space between the superior and inferior nuchal lines gives insertion medially to the semispinalis capitis and laterally, from above downwards, to the splenius capitis and obliquus capitis superior. The inferior nuchal line gives insertion over its outer part to the rectus capitis posterior major. The inner third of this line and the surface between that extent of it and the foramen magnum give insertion to the rectus capitis posterior minor.



F!g. 115. — The Occipital Bone (External View).


The anterior or internal surface is irregularly concave and divided into four fossae by two ridges—a longitudinal, extending from the superior angle to the foramen magnum, and a transverse, extending from one lateral angle to the other. At the point where these two ridges intersect there is the internal occipital protuberance. The upper half of the longitudinal ridge gives attachment to a portion of the falx cerebri, and is marked by a groove for the superior sagittal venous sinus, this groove being confined to one side of it, usually the right. The lower half is sharp and wiry, and is called the internal occipital crest. It gives attachment to the falx cerebelli, and is occasionally grooved for the occipital venous sinus. Near the foramen magnum it divides into two parts, which diverge as they pass to that opening, and enclose between them the vermian fossa, which receives a part of the vermis of the cerebellum. The transverse ridge gives attachment to the tentorium cerebelli, and is deeply grooved along each half of the tiansverse venous sinus. On one side of the internal occipital protuberance, usually the right, there is a wide depression, at which point the longitudinal groove is continued into the corresponding lateral groove. This depression lodges the torcular Herophili (or confluence of the sinuses) , which is a dilatation formed where the superior sagittal sinus bends sharply to become continuous with the right transverse sinus. The four fossae are arranged in a superior pair, called superior occipital or cerebral, and an inferior pair, called inferior occipital or cerebellar. Each cerebral fossa presents a number of digitate impressions for the convolutions of the occipital lobe of t e ceiebrum, which is lodged in it. The cerebellar fossae, which are separated by the internal occipital crest, are smooth, but may show ransverse striations. They are much thinner then the cerebral, and lodge the hemispheres of the cerebellum.


The angles are superior and two lateral. The superior angle forms e lghest part of the bone, and fits in between the postero-superior angles of the panetals. The lateral angles are situated at either end ot the transverse ridge on the internal surface.


The borders are two superior and two inferior. Each superior border extends from the superior angle to the lateral angle, and is serrated for the posterior border of the corresponding parietal. Each inferior border extends from the lateral angle to the jugular process, and is famtiy serrated for the mastoid portion of the temporal. ?

wm a u llar - pa ? ]^ as ^" occi pi tal ) is a compressed quadrilateral maprinm 1C S ' forwards and upwards in front of the foramen

rail pH fuh h $ superior surface presents a broad median depression, to tbr f asl ar £ roove > which is sloped downwards and backwards either cHHp. ma § num » an d lodges the medulla oblongata. At Detrosal vrnn ls g 100v e there is a narrow groove for the inferior the S ! nus .‘ J be 1 nferior surface presents at its centre

either^^sTde nf f f ? r t he fibrous ra P h e of the pharynx. On

the insertion of th ^ ^ 6 tbere is a r °ugh, oblique impression for

insertion of the longus capitis, and between the outer part of this


impression and the foramen magnum the surface gives insertion to the rectus capitis anterior. Ihe anterior border is thick, rough, and truncated, and up to the twentieth year it articulates with the body of the sphenoid by synchondrosis, but thereafter ankylosis takes place. The posterior border , which is thin, smooth, and concave, bounds anteriorly the foramen magnum, and sometimes presents a third occipital condyle of small size for articulation with the tip of the odontoid process of the axis. This border gives attachment to the



Fig. 116.—The Occipital Bone (Internal View).


apical ligament of the odontoid process. Each lateral border is thick and rough for the petrous portion of the temporal.

The condylar portions (exoccipitals) are placed on either side of the foramen magnum, where they extend as far back as its posterior margin, and very nearly as far forwards as its anterior margin. Each bears on its under surface the greater part of a condyle. The condyles are oval, convex, and covered by cartilage, and they articulate with the superior articular processes of the atlas. Their long axes are directed forwards and inwards, and the direction of each surface is downwards and slightly outwards. They do not extend farther back on the lateral margins of the foramen magnum than the level of the centre, and the front part of each belongs to the basilar portion. The circumference of a condyle gives attachment to the capsular ligament of the corresponding atlanto-occipital joint, and on the inner aspect of each there is a tubercle for the alar ligament. Lateral to the front of each condyle is the anterior condylar canal, which opens forwards and outwards from the cranial cavity. It transmits the hypoglossal nerve and a meningeal branch of the ascending pharyngeal artery. Behind each condyle is the posterior condylar fossa, which may be pierced by a posterior condylar canal, on one or both sides, for an emissary vein passing between the intracranial transverse (sigmoid) sinus and the extracranial suboccipital venous plexus. The part external to the condyle is called the jugular process, which lies above the transverse process of the atlas, and is homologous with it. Posteriorly it is continuous with the tabular portion, and anteriorly it presents the jugular notch, which, with the jugular fossa of the petrous portion of the temporal, forms the jugular foramen. Superiorly it presents a short, but deep and wide, groove for a portion of the sigmoid venous sinus just before it leaves by the jugular foramen. This groove may be pierced by a posterior condylar canal. Interiorly it gives attachment to the rectus capitis lateralis, and may send downwards a projection towards the transverse process of the atlas, which represents the paroccipital process of comparative anatomy. Laterally the jugular process articulates with the jugular facet on the petrous portion of the temporal by synchondrosis up to the twenty-fifth year, after which ankylosis takes place.

The foramen magnum is situated at the lower and anterior part of the bone, and is oval, its long axis extending from before backwards. The anterior margin, in front of the condyles, gives attachment to the anterior atlanto-occipital membrane, and, behind them, to the posterior atlanto-occipital membrane. The foramen transmits the central nervous axis and its membranes, the spinal accessory nerves, the vertebral arteries, the anterior spinal arteries, meningeal branches of the ascending pharyngeal artery, and parts of the cerebellar amygdalae.

The chief blood-supply of the bone is derived from the occipital and posterior auricular arteries.

Articulations. —Superiorly with the parietals, laterally with the temporals (mastoid and petrous portions), anteriorly with the sphenoid, and inferiorly with the atlas, and in rare cases with the odontoid process of the axis.

Structure. —The occipital, being a tabular bone, is composed of

two tables of compact bone, with cancellous tissue, called diploe, between them.

Varieties. (1) There may be a minute foramen piercing the external occipital protuberance for an emissary vein, which passes between the intraeianial torcular Herophili and one of the tributaries of the extracranial occipital vein. (2) The upper division of the tabular portion may be separate, representing the interparietal bone of comparative anatomy, and it may be in one piece, or in two or more. (3) The semilunar area between the highest and superior nuchal lines may be prominent, constituting the torus occipitalis transversus. (4) The anterior condylar canal may be double on its cranial aspect. (5) There may be a third occipital condyle on the anterior margin of the foramen magnum. (6) There may be a paroccipital process on the under aspect of the jugular process. (7) The condyle may be divided into two parts, anterior and posterior. (8) There may be an intrajugular process on the front of the jugular notch, which may extend as far as the petrous portion of the temporal. (9) The upper angle may form a separate bone, known as the pre-interparietal.

Ossification. —The bone is developed in four parts. The squamous portion usually ossifies from four centres, which appear around the internal occipital protuberance about the eighth week of intra-uterine life. Two are deposited in cartilage, one for each cerebellar fossa, which soon fuse and give rise to the lower or supra-occipital division. The other two are deposited in membrane, one in each cerebral fossa, which also soon fuse, and give rise to the upper or interparietal division. Indeed, as a general rule, all four ultimately blend.



Fig. 117.—Ossification of the Occipital Bone. The figure shows the condition of the bone at birth.


There may, however, be two other centres for the interparietal portion, placed on either side of the middle line not far from the future superior angle, which occasionally remain as separate ossicles, or they may fuse and give rise to the pre-interparietals. The interparietal portion may remain separate from the supra-occipital, with which it may be connected by a suture, or they may be separated by a partial fissure. Fissures, which persist for some time after birth, intersect the tabular part at the superior and lateral angles, and a membranous interval extends from the protuberance to the foramen magnum in early life, which remains for some weeks, after which it is replaced by bone. It is in this latter situation that an encephalocele may occur. The basilar and condylar parts have each one centre appearing in cartilage about the ninth week, the anterior part of each condylar portion deriving its ossification from the basilar centre. At birth the bone is in four parts, connected by cartilage. Union between the tabular and condylar portions is completed by the fifth year, and the condylar and basilar portions unite about the sixth year. Between seventeen and twenty the basilar portion joins the sphenoid, and at the twenty-fifth year the jugular process becomes ankylosed to the petrous portion of the temporal.

Obstetrical Hinge-Joint (of Budin). —At birth the tabular or squamous portion of the occipital bone is connected with the two condylar portions by a band of cartilage. This region is known as the obstetrical hinge-joint (of Budin). The connection is such as to allow of limited swinging or see-saw movements in front of, and behind, the cartilaginous band, by which movements the diameters and form of the child’s head are liable to be modified during labour.

The Parietal Bones.

The parietal bones are so named because they form a large part of the cranial wall. They lie between the frontal and occipital, and superiorly they articulate with each other by the sagittal or interparietal suture. Each bone is quadrilateral and curved, and presents

Superior Border


two surfaces, four borders, and four angles. The external surface is convex, and near its centre is more elevated than elsewhere, this part, from which ossification originally proceeds, being called the parietal eminence. About this spot the surface is crossed from before backwards by two curved lines, called the superior and inferior temporal ines, the narrow space between which is smoother and more glistening an the rest of the surface. The part above the superior line is covered by the epicranial aponeurosis, and the ridge itself gives attachmen to the temporal fascia. The inferior temporal ridge limits the origin °i the temporal muscle, and the portion between it and the in erior border, which is vertically striated and called the planum empora e, forms a part of the temporal fossa, and gives origin to fibres


of the temporal muscle. Near the superior border, about an inch in front of the postero-superior angle, may be the parietal foramen, for an emissary vein which passes between the intracranial superior sagittal sinus and one of the tributaries of the extracranial occipital vein.

The internal surface is concave, its deepest part, opposite the parietal eminence, being known as the parietal fossa. This surface presents a number of digitate impressions for the convolutions of the parietal and part of the frontal lobes of the cerebrum, and a system of branching meningeal grooves for the divisions of the middle meningeal artery. These begin as two grooves, each of which soon becomes arborescent. The anterior, the larger of the two, starts at the antero Superior Border and Groove for Superior Sagittal Sinus Depressions for ,

Arachnoideal Granulations >


inferior angle, where it may be bridged over into a short canal, and the posterior begins at the centre of the inferior border. Superiorly, close to the upper border, there is a half groove which, with that of the opposite bone, lodges the superior sagittal venous sinus. Along the course of this groove, but lateral to it, are several depressions, best marked in old persons, which lodge the arachnoideal granulations (Pacchionian bodies). Close to the postero-inferior angle there is a short groove for part of the transverse venous sinus.

Borders.—The posterior, anterior, and superior borders are serrated. The posterior border articulates with the occipital; the superior , with its fellow; and the anterior with the frontal. The anterior border is bevelled below at the expense of the inner plate, where it overlaps the frontal, and it is slightly bevelled above at the expense of the outer plate, where it is overlapped by the frontal. The inferior border , which is the shortest, is for the most part concave and markedly bevelled at the expense of the outer plate, where it is overlapped by the squamous portion of the temporal. Posteriorly, however, it is serrated for the superior border of the mastoid portion of the temporal.

Angles.—The anter o-superior angle, with its fellow, lies in the situation of the original anterior fontanelle or bregma. The posterosuperior angle, with its fellow, occupies the region of the original posterior fontanelle or lambda. The postero-inferior angle is truncated, and articulates with the mastoid portion of the temporal, being also recognized by the short groove for the transverse venous sinus on its inner aspect. This region is the asterion. The antero-inferior angle is prolonged and pointed, and articulates with the great wing of the sphenoid, being also recognized by the large anterior meningeal groove on its inner surface.

Occasionally the parietal fails to articulate with the sphenoid at this point, which is known as the pterion. In that case the frontal will meet the temporal, as it usually does in monkeys, and may be regarded as an atavistic or retrogressive variation, or there may be a Wormian bone known as the epipteric ossicle.

Articulations .—Posteriorly with the occipital, superiorly with its fellow, anteriorly' with the frontal, antero-inferiorly with the sphenoid, and inferiorly with the temporal.

Structure. — It is a characteristic tabular bone.

Varieties. —(i) The bone may persist in two parts, upper and lower, connected by an antero-posterior suture. (2) The parietal foramen may be absent on one or both sides.

Ossification. —The parietal ossifies in membrane from two centres, which appear about the seventh week in the region of the future parietal eminence, one above and the other below it, and soon coalesce. The ossification radiates from this point in such a manner as to leave a notch on the upper border a little in front of the postero-superior angle, which forms one-half of the sagittal fontanelle of the earlier half of foetal life, the lateral part of which persists as the parietal foramen.



Fig. 120. — Ossification of the Parietal Bone.


The Frontal Bone

The frontal bone forms the forehead and greater part of the roof ot each orbit, and it lies in front of the parietals. It is divisible into a frontal portion and two orbital plates, the latter being situated interiorly, where they are separated by the ethmoidal notch.



The frontal portion presents two surfaces, external and internal. The external surface, which is smooth and convex, has, a little below its centre, on either side, an elevation, called the frontal eminence. Below this, and separated from it by a shallow groove, there is the curved superciliary arch (or ridge). This ridge is prominent medially, but it subsides laterally. It supports the upper half of the orbicularis oculi, and internally it gives origin to the corrugator, whilst the surface above each ridge supports the frontalis and part of the epicranial aponeurosis. Between the two superciliary ridges is an elevation, called the glabella. Below each ridge is the curved supra-orbital margin, which is most prominent in its outer two-thirds. At the junction of the inner third and outer two-thirds is the supra-orbital notch, sometimes a foramen, for the passage of the supra-orbital nerve and artery. Occasionally there is a frontal notch, inside the normal notch, for a branch of the supra-orbital nerve. The extremities of the supra-orbital arch form the medial and zygomatic processes. The medial process is stout and serrated for articulation with the zygomatic bone. The internal angular process is faintly marked, and lies by the side of the nasal notch, where it articulates with the maxilla, and gives origin to some fibres of the orbicularis oculi.

On the lateral aspect of the external surface a ridge runs upwards and at first a little inwards from the zygomatic process. This is the beginning of the temporal line, and, at a higher level, divides into the two which are continued on to the parietal bone, though in order to do so they have to arch backwards and upwards. The superior gives attachment to the temporal fascia, and the inferior limits the temporal muscle, which arises from it and the surface below, this latter forming a part of the temporal fossa. Below the glabella on the under aspect there is a rough, semilunar, serrated surface for articulation with the nasal bones and nasal processes of the maxillae, and behind this is the nasal notch, bounded at either side by the internal angular process. Within the notch is the nasal process, which supports the nasal bones, and projecting downwards from it is the sharp nasal spine, which articulates in front with the upper part of the crest of the nasal bones, and behind with the perpendicular plate of the ethmoid. This spine enters into the nasal septum. On either side of the spine is the ala, which is grooved to take part in the roof of the corresponding nasal fossa.

The internal or cerebral surface of the frontal portion is concave, and in the middle line presents a groove, called the sagittal sulcus, which lodges a part of the superior sagittal venous sinus. On either side of the upper part of this groove there are a few depressions for the arachnoideal granulations. Interiorly the groove is replaced by the frontal crest, which terminates at the foramen caecum. This foramen is sometimes partly formed by the crista galli of the ethmoid, and it may be closed below, or it may transmit an emissary vein, which passes between the intracranial superior sagittal sinus and the veins of the roof of the nose. The internal surface shows numerous digitate impressions for the convolutions of the frontal lobes of the cerebrum, and laterally there are a few meningeal grooves, transversely disposed, for branches of the middle meningeal arteries.

The supero-lateral or parietal border of the frontal portion is serrated for the parietal bones. Superiorly it is slightly bevelled near the middle line at the expense of the inner plate, where it overlaps the parietal, and at either lower extremity it is distinctly bevelled at the expense of the outer plate, where it is overlapped by the parietal. It will be appreciated that this arrangement enables the bones to support one another mutually. Internal to its lower termination at either side theie is a iough triangular surface, which is serrated for the great wing of the sphenoid. 6



Pig. 121. The Frontal Bone (Anterior View).



Ihe orbital plates, thin and brittle, project backwards in a curved r om the supra-orbital margins, and are widely separated by n which is occupied by the cribriform plate of the

Ax^T-rie a aC ^ ls t nan gular, with the truncated apex directed back Tu p • mwar( ts, and presents two surfaces and three borders. -lio-i+ahf° r - cereh l al sur f ac e is irregularly convex, and marked by frontal 1 1I ?P ress * c ? n s ^° r conv °t u tions of the orbital surface of the o e, w ich rests upon it. The inferior or orbital surface smooth and concave, forms the principal part of the roof of the orbit. Within the zygomatic process is the lacrimal fossa, which lodges the lacrimal gland, and near to the internal angular process is the small trochlear fossa, which gives attachment to the trochlea of the superior oblique muscle of the eyeball.

The borders are anterior, external, and internal. The anterior border represents the supra-orbital margin, and is free. The external border is sharp and irregular, and its direction is backwards and inwards. It forms a right angle with its fellow of the opposite side, and abuts against the great wing of the sphenoid. The internal border is directed from before backwards, is parallel with its fellow of the opposite side, and forms the lateral boundary of the ethmoidal notch. It is bevelled at the expense of the lower plate, and the bevelled surface presents several excavations, which close in the ethmoidal cells on the upper border of the labyrinth of the ethmoid. This surface is crossed by two transverse grooves, anterior and posterior, which, with similar grooves on the contiguous part of the ethmoid, form the anterior and posterior ethmoidal (internal orbital) foramina. These open on the inner wall of the orbit, and the anterior gives passage to the anterior ethmoidal vessels and nerve, whilst the posterior transmits the posterior ethmoidal vessels and nerve. The truncated apex of the orbital plate articulates with the small wing of the sphenoid.




Fig. 122. — The Frontal Bone (Inferior View).



In front of the anterior ethmoidal groove on either side is the opening of the frontal air sinus. Each leads into a cavity within the bone, which extends outwards from near the middle line for a variable distance behind the superciliary arch. The sinuses are separated by a septum which is seldom really median, and may be unilocular or multilocular. In the latter case the subdivisions may extend backwards within the roof of the orbit, which always provides the easiest way of laying them open because the bone here is so thin. Each sinus is lined by mucous membrane continuous with that of the corresponding nasal fossa, with which it communicates by a passage called the infundibulum.


Articulations. — These are twelve in number, as follows: posteriorly with the two parietals above, and the sphenoid (great and small wings) below; by the zygomatic processes with the two zygomatic bones, between the orbits with the two nasals, two maxillae, and two lacrimals; and in the middle line with the labyrinths and perpendicular plate of the ethmoid.

Structure.—It is a tabular bone. The orbital plates, being destitute of diploe, are thin and translucent, except in those cases where extensions of the frontal air sinuses invade them.


Varieties. —(1) There is in about 10 per cent, of all cases a persistent frontal suture, called the metopic suture, this condition being known as metopism. (2) Wormian bones are sometimes met with at the centre of the supero-lateral border in the region of the anterior fontanelle, and, if these remain permanent, they give rise by their union to a bregmatic bone.


Appears about the 7th Week (intra-uterine)

Fig. 123.—Ossification of the Frontal Bone.

one for each zygomatic process. The hrst few years, but do not attain any larger in the male than in the female.


Ossification. —The frontal ossifies in membrane from two centres, one for each half, which appear about the seventh week of intra-uterine life in the situation of the future frontal eminences. At birth the bone consists of two halves united by membrane, and in the course of the first year they become united by a vertical frontal or metopic suture. This suture gradually becomes obliterated from above downwards, and usually disappears in the second year, though slight traces may persist above and below, especially in the latter situation. Three pairs of secondary centres are described, two medially placed for the nasal spine, one at either side in the region of the future trochlear fossa, and frontal air sinuses begin to appear in the size till after puberty. They are rather


The Temporal Bones

The temporal bones (ossa temporis) are so named because the hair over the temple is the first to become grey, thus indicating advance m life. Each bone is situated on the lateral aspect of the head below , e P ane tal. For convenience of description each is divided into iree parts namely, the squamous portion, which bears the zygoma; the mastoid portion; and the petrous portion, which bears interiorly the styloid process.

The squamous portion (squamo-zygomatic) lies almost vertically, and presents two surfaces, outer and inner, and a superior border. The outer surface is convex towards its centre, and forms a large part of the temporal fossa. It gives origin to fibres of the temporal muscle, and is marked by a groove for the middle temporal artery, which extends upwards and slightly forwards from a point just above the external auditory meatus to the superior border. The inner surface, which is concave, is related to the temporal lobe of the cerebrum, and presents a few digitate impressions and meningeal grooves. The superior border is much arched, and describes about two-thirds of a circle. Except over the lower part of its anterior portion, it is markedly bevelled at the expense of the inner plate for the parietal, which it overlaps. Anteriorly over its lower part it is thick and serrated for the lateral border of the great wing of the sphenoid. The place of junction of the squamous and petrous portions is indicated at the lower part of the inner surface of the former by the narrow petrosquamous groove or suture.

The zygoma or zygomatic process springs from the lower part of the outer surface of the squamous portion. Its base is compressed from above downwards, and directed outwards. It then undergoes a twist, and is directed forwards in a curved manner, being laterally compressed. This part of it presents two borders, two surfaces, and an extremity. The superior border, sharp and convex, extends farther forwards than the inferior, and gives attachment to the temporal fascia in two divisions. The inferior border gives origin to fibres of the masseter. The outer surface is convex and subcutaneous, whilst the inner, which is concave and looks towards the upper part of the zygomatic fossa, gives origin to fibres of the deep part of the masseter. The extremity is bevelled at the expense of the lower border, and serrated for the zygomatic. The base of the zygoma presents two roots, anterior and posterior. The anterior root, which is continuous with the inferior border of the process, is directed inwards in front of the mandibular fossa. It is at first narrow, but subsequently thick and convex, where it is covered by cartilage. This portion is called the articular tubercle, and in front of it there is a small non-articular triangular area marked off from the articular surface by a sinuous line and looking into the zygomatic fossa. The posterior root, which is continuous with the superior border of the process, passes backwards above the external auditory meatus, then between the squamous and mastoid portions, where it is known as the supramastoid crest, and finally it turns upwards, where it forms part of the posterior boundary of the temporal fossa. In front of the external auditory meatus it sends downwards a short offshoot, which lies between the external auditory meatus and the anterior part of the mandibular fossa. This is called the postglenoid tubercle, and is sometimes referred to as the middle root of the zygoma.


On the outer surface of the zygoma, above the place where the anterior root becomes continuous with its lower border, there is a projection, called the preglenoid tubercle, which gives attachment to the temporo-mandibular of the temporo-mandibular articulation.

Behind the anterior root is the mandibular fossa, which extends on to the tympanic plate. It is elongated from before backwards and inwards, and is divided into two parts by the fissure of Glaser. The anterior part, which belongs to the squamo-zygomatic portion of the bone, is covered by cartilage, and is triangular, with the apex at the preglenoid tubercle and the base at the squamo-tympanic fissure. It is deeply concave, and is bounded anteriorly by the articular tubercle, externally by the commencement of the posterior root of the zygoma, and posteriorly from without inwards by the postglenoid tubercle and squamo-tympanic fissure. It articulates with the condyle of the inferior maxilla when the mouth is closed, an interarticular fibrocartuage intervening; but, when the mouth is open, the condyle with the fibro-cartilage moves forwards on to the articular tubercle. The posterior part of the mandibular fossa is situated behind the squamotympanic fissure, and is formed by the tympanic plate, which separates it rom the external auditory meatus. It is shallow, non-articular,



Fig. 124. — The Right Temporal Bone (External View).


and quadrilateral, and it lodges the deep part of the parotid gland when the mouth is open.

The squamo-tympanic fissure (fissure of Glaser) is closed in its outer part, and is divided into two medially by means of a thin plate which descends from the tegmen tympani, and forms the chief part of the outer wall of the canals for the osseous part of the pharyngotympanic tube and tensor tympani muscle. Between this plate and the tympanic plate the anterior process of the malleus is located internally, and there is a small opening leading to the tympanic cavity for the passage of the anterior tympanic branch of the maxillary artery and the anterior ligament of the malleus (so-called laxator tympani muscle) or band of Meckel. At the inner end of the squamo-tympanic fissure is another minute opening leading from the tympanic cavity, called the anterior canaliculus for chorda tympani (canal of Huguier, iter chordae anterius), which transmits the chorda tympani nerve.

The mastoid portion is so named from the mastoid process which it bears. It is limited above by the supramastoid crest and its own superior border, in front by the external auditory meatus and tympanomastoid fissure, and behind by its posterior border. It presents two surfaces and two borders. The external surface , rough and convex, is prolonged downwards behind the external auditory meatus into the mastoid process, which presents on its inner surface two grooves. The outer, called the mastoid notch, is deep, and gives origin to the posterior belly of the digastric; and the inner, called the occipital groove, is narrow, and lodges the occipital artery. The upper part of the outer surface of the mastoid process gives origin over its posterior half to the auricularis posterior and part of the occipitalis in this order from before backwards; and lower down it gives insertion to the sterno-mastoid, splenius capitis, and longissimus capitis, in this order from above downwards. At the upper and back part of the mastoid portion, a little below the supramastoid crest, there may be the remains of the squamo-mastoid suture directed downwards and forwards, indicating the line of junction of the squamo-zygomatic and basal part of the petrous portions. Directly in front of the root of the mastoid process there is an important depressed area, called the suprameatal triangle (Macewen), which is bounded as follows: above by part of the posterior root of the zygoma, below by the postero-superior part of the external auditory meatus, and behind by a vertical line connecting the upper and lower boundaries, which line is continuous with the posterior part of the external auditory meatus. In the lower part of the suprameatal triangle is the suprameatal spine, a sharp, anteroposterior scale of bone, which gives attachment to a portion of the cartilage of the external ear. The outer surface of the mastoid portion presents several small nutrient foramina, and often there is a large opening, called the mastoid foramen, usually placed near the posterior border, for a large emissary vein, which passes between the sigmoid sinus internally and the outermost tributary of the occipital vein, or the posterior auricular vein externally. In addition to these, there is the minute arterial fissure on the outer surface of the mastoid process below its centre for the mastoid branch of the occipital artery.

The inner surface presents the deep sinuous sigmoid groove, which lodges a part of the sigmoid venous sinus, and from which the mastoid foramen opens. The genu or bend of this groove and its descending limb lie behind the mastoid antrum.

The superior border, thick and serrated, articulates with the back part of the inferior border of the parietal. Near its anterior part it presents the parietal notch, which receives a portion of the parietal bone. The posterior border, also thick and serrated, articulates with the inferior border of the squamous portion of the occipital.

The interior of the mastoid portion contains a number of cavities lined with mucous membrane, called the mastoid air cells. These open into an irregular chamber, known as the mastoid antrum, which is situated behind the upper part of the posterior wall of the tympanic cavity, and is lined by mucous membrane continuous with that of the tympanum and mastoid cells. The upper part of the antrum communicates with the epitympanic recess or attic of the tympanic cavity by an opening which faces that of the pharyngo-tympanic tube, but the lower part is shut off from the tympanic cavity, and its floor is on a lower level than the floor of that cavity, which explains the difficulty in the drainage of fluid. The roof of the antrum, called tegmen antri, is continuous with the tegmen tympani, and both enter into the formation of the middle fossa of the base of the skull. The lateral wall is formed by the squamo-mastoid junction in the region of the supra meatal triangle, and if the bone is drilled here the antrum is reached with great certainty; the floor and medial wall are constructed by the petro-mastoid portion; and the posterior wall represents that part of the mastoid portion which bears the genu or bend and descending limb of the sigmoid groove. Ihe mastoid air cells extend from the antrum into the mastoid portion in a backward and downward direction, and are subject to variety as regards number and size. They are arranged in two groups—horizontal or superior, and vertical or inferior. The former are purely pneumatic or air cells, but the latter are of two kinds, the upper ones containing air, and the lower ones, which extend to the tip of the mastoid process, being diploic— i.e., containing marrow and of large size. These diminish as age advances. Superiorly the cells extend forwards over the roof of the external auditory meatus, upwards as high as the supramastoid crest, and inwards for a certain distance into the petrous portion. They may also extend into the jugular process of the occipital in old persons. At birth the mastoid cells are not developed, but the antrum is present.

The petrous portion is so named from its rocky consistence, and its ~- r ' ec ^ lon is inwards and forwards into the base of the skull. It has ^ 6 ? .P e . a three-sided pyramid, and presents three surfaces (one ot which is concealed by the tympanic plate), three borders, an apex, an base. The surfaces are anterior, posterior, and inferior.

Ihe anterior surface, which has an inclination forwards, looks into the middle fossa of the base of the skull, and towards its outer part presents a few digitate impressions for convolutions of the temporal lobe of the cerebrum. Near the apex is the trigeminal impression for the trigeminal ganglion, and below this is the outlet of the carotid canal for the internal carotid artery. Proceeding backwards and outwards, there is a small groove leading to a foramen called the hiatus for greater superficial petrosal nerve (hiatus Fallopii), transmitting the nerve of that name along with the petrosal branch of the middle meningeal artery. Below and parallel to this groove is a smaller one lodging the lesser superficial petrosal nerve and leading to the hiatus for lesser superficial nerve. This latter, however, with the nerve, is inconstant. Behind and lateral to the hiatus for greater superficial petrosal nerve is an elevation, called the arcuate eminence, which coincides with the position of the superior semicircular canal of the internal ear, and if the bone is perforated just in front of this the tympanic cavity will be opened up. Between this eminence and the hiatus for greater superficial nerve medially and the petro-squamous fissure laterally there is a plate of bone, called the tegmen tympani, which forms the roof of the tympanic cavity and of the canal for the tensor tvmpani muscle.



Fig. 125. — The Right Temporal Bone (Internal View).


The posterior surface, which looks backwards and inwards, forms part of the posterior cranial fossa. It presents about its centre a large opening, which leads into a short canal, called the internal auditory meatus, for the passage of the motor and sensory roots of the facial nerve and auditory nerves, and the internal auditory artery. At the deep end of this meatus there is a perforated plate of bone, known as the lamina cribrosa, which is divided into an upper and a lower fossa by a transverse ridge, called the transverse crest. The upper fossa presents at its anterior part a special foramen which leads into the facial canal, and by this foramen the facial nerve leaves the meatus. The remainder of the upper fossa is known as the superior vestibular area (area cribrosa superior), and it is pierced by the nerves and arteries destined for the utricle and the ampullae of the superior and lateral semicircular canals. The lower fossa contains the cochlear area, which is pierced by the cochlear nerves and arteries, the inferior vestibular area for the nerves and arteries to the saccule, and the foramen singulare



Fig. 126.—Plan of Fundus of Right Internal Auditory Meatus, showing the Various Openings Ind their Relation to the Crista Falciformis.

The cross indicates the directions anterior, posterior, superior, and inferior.

for the nerves and arteries to the ampulla of the posterior semicircular canal. The facial canal, for the facial nerve, extends from the deep end of the internal auditory meatus to the stylo-mastoid foramen, between which points it takes a very circuitous course. It passes at hrst horizontally outwards between the cochlea and vestibule to the inner wall of the tympanum, then it bends sharply backwards, lying above the fenestra vestibuli, and finally, making another abrupt bend, it descends in the angle between the inner and posterior walls of the tympanic cavity to the stylo-mastoid foramen. The hiatus for greater superficial petrosal nerve leads from the commencement of the facial canal to the anterior surface of the petrous portion, and, as stated, transmits the great superficial petrosal nerve. The facial canal, as it descends behind the tympanic cavity, communicates with the canal of the pyramid by an opening through which the nerve to the stapedius reaches that muscle, and below the pyramid it presents another openmg, called the posterior canaliculus for chorda tympani, by which the chorda tympani nerve passes into the tympanic cavity.


About J inch lateral to and below the opening of the internal auditory meatus there is a narrow fissure, overhung by a thin scale of bone, called the aquaeduct of vestibule, which contains a small artery and vein, and the endolymphatic duct or its remnants. Close to the superior border, about midway between the opening of the internal auditory meatus and the aquaeduct of vestibule, there is a depression containing a small opening, known as the subarcuate fossa, which represents the parafloccular fossa of early life.

The inferior surface appears on the exterior of the base of the skull. Near the apex there is a large rough surface which gives origin to fibres of the tensor tympani and levator palati, and behind this a circular opening, called the carotid canal, which is the inlet to the carotid canal.


Fig. 127. — Section through the Petrous and Mastoid Portions of the Temporal Bone, showing the Tympanum and Mastoid Cells.

This canal, which transmits the internal carotid artery and the carotid sympathetic plexus, passes at first vertically upwards , and then, bending at a right angle, it passes horizontally forwards and inwards, to open at the apex, below the trigeminal impression, into the foramen lacerum. On the posterior wall of the vertical portion of the canal is a minute carotico-tympanic canaliculus for the tympanic branch of the carotid sympathetic plexus and carotico-tympanic branch of the internal carotid artery. Behind the carotid foramen is the jugular fossa, which, with the jugular notch of the occipital, forms the jugular foramen. On the outer wall of this fossa, near the root of the styloid process, there is the opening of the mastoid canaliculus for the auricular branch (Arnold’s nerve) of the vagus. On the carotid ridge, between the carotid canal and the jugular fossa, is the opening of the canaliculus for tympanic nerve for the tympanic branch (Jacobson’s nerve) of the glosso-pharyngeal and the inferior tympanic branch of the ascending pharyngeal artery. Behind the jugular fossa, medial to the stylomastoid foramen, is the rough jugular facet for articulation with the extremity of the jugular process of the occipital by synchondrosis up to the twenty-fifth year, after which ankylosis takes place. Lateral to the jugular facet is the styloid process, immediately behind the root of which is the stylo-mastoid foramen. This foramen is the outlet of the facial canal, and by it the facial nerve makes its exit, whilst the


Fig. 128. — The Right Temporal Bone (Inferior View).

stylo-mastoid branch of the posterior auricular artery passes in. A little behind the stylo-mastoid foramen, between the mastoid process and tympanic plate, is the tympano-mastoid fissure for the exit of the auricular branch of the vagus nerve.

Either ensheathing or passing just in front of the root of the styloid process is a sharp ridge of bone running inwards and a little forward; it is known as the vaginal process, and it will be noticed that it is really t * ie i? wer * ree border of the tympanic plate described on p. 194.

I he borders are anterior, superior, and posterior. The anterior )or er separates the anterior from the inferior surface. It is very short, and forms an acute angle with the squamous portion, within which the posterior pointed extremity of the great wing of the sphenoid is received. This angle presents an opening for the exit of the pharyngotympanic tube: the canal to which it leads is divided into two compartments by a thin transverse shelf of bone, scooped out on its under surface, called the processus cochleariformis. The upper small compartment lodges the tensor tympani muscle, and the lower large one forms the osseous part of the pharyngo-tympanic tube. Both of these canals lead upwards and backwards to the anterior part of the tympanic cavity. The superior border , which is the longest, separates the anterior from the posterior surface. It gives attachment to the tentorium cerebelli, and is grooved for the superior petrosal venous sinus. The anterior part of this border frequently presents a process, which projects over the upper end of the groove for the inferior petrosal venous sinus, and gives attachment to the petro-sphenoidal ligament. This ligament connects it with the lateral border of the dorsum sellce of the sphenoid (which may present a superior petrosal process), and, if it ossifies, it bridges over a foramen through which the inferior petrosal sinus and sixth cranial nerve pass. The posterior border separates the posterior from the inferior surface. Its outer part, opposite the jugular fossa, enters into the formation of the jugular foramen, and its inner part presents a groove for the inferior petrosal sinus, and articulates with the side of the basilar portion of the occipital. In line with the opening of the internal auditory meatus it presents a triangular depression, which encroaches on the inferior surface and leads to a small canal, called the aqueduct of cochlea. This aqueduct transmits a small vein from the cochlea to the inferior petrosal sinus, and also a communication between the perilymph of the scala tympani and the subarachnoid space, sometimes called the perilymphatic duct.

The apex of the petrous portion presents the outlet of the carotid canal inferiorly.

The base is the part of the petrous portion which appears on the external surface, and it presents a large opening leading into the external auditory meatus. This opening is oval, its long axis lying downwards and backwards, and it is bounded above by the posterior root of the zygomatic process, whilst the remainder of its circumference is formed mainly by the external auditory process of the tympanic plate. The canal of the external auditory meatus* is formed chiefly by the tympanic and squamous portions, but also slightly by the mastoid portion. Its direction is inwards, slightly forwards, and finally downwards, its length being rather more than J inch (14 millimetres). It leads to the tympanic cavity, and its deep end, which is nearly circular, is closed by the tympanic membrane. This membrane is placed obliquely, and forms an acute angle with the lower wall, and an obtuse angle with the upper, so that the floor of the meatus is

Unfortunately the term ‘ external auditory meatus ’ is applied not only to the canal, but to its external opening and to the opening in the soft parts, which lies still more external as well as a little lower.


longer than the roof, the anterior wall being also longer than the posterior. Its floor presents a slight elevation at the centre, where the passage is narrower than elsewhere, this portion being called the

isthmus.

The tympanic part is situated behind the squamo-tympanic fissure, and is quadrilateral. It presents two surfaces and four borders. The external surface forms the posterior part of the mandibular fossa, and lodges the deep portion of the parotid gland. The internal surface forms the anterior, inferior, and part of the posterior walls of the external auditory meatus, and the anterior and inferior walls of the tympanic cavity, and at its inner or deep end it presents a groove, deficient above, for the tympanic membrane, called the tympanic groove. The outer border forms the external auditory process, and is curved and rough for the cartilage of the auricle. The inner border is situated immediately outside the bony part of the pharyngo-tympanic tube, and is short and irregular. The upper border bounds the squamotympanic fissure posteriorly, and the lower border forms at its back part the vaginal process, which ensheathes the base of the styloid process externally. The tympanic plate sometimes presents a small deficiency at its centre, called the foramen of Huschke, which is always present until after five years of age.

The styloid process, which is cylindrical and tapering, starts from a point immediately in front of the stylo-mastoid foramen, and is directed downwards and inwards. The muscular and ligamentous relations of the process are as follows: The stylo-pharyngeus muscle arises from the inner aspect of the base; the stylo-hyoid muscle from the posterior and outer aspect of the process near its base; the styloglossus muscle from the front of the process near its tip; the stylomandibular ligament is attached to it just below the stylo-glossus; and the stylo-hyoid ligament is attached exactly to the tip.

The blood-supply of the bone is chiefly derived from the following sources: The squamous portion receives externally branches from the deep temporal arteries of the maxillary, and internally branches of the middle meningeal. Other arterial twigs enter the bone at definite points as follows: internal auditory from the basilar, through the internal auditory meatus; petrosal from the middle meningeal, through the hiatus for greater superficial petrosal nerve; stylo-mastoid from the posterior auricular, through the stylo-mastoid foramen; anterior tympanic from the maxillary, through the squamo-tympanic fissure; inferior from the ascending pharyngeal, through the canaliculus for tympanic nerve; carotico-tympanic from the internal carotid, through the carotico-tympanic canaliculi on the posterior wall of the vertical portion of the carotid canal; the mastoid from the occipital, through the mastoid foramen on the outer surface of the mastoid process; and twigs from the mastoid division of the posterior auricular, through the foramina on the outer surface of the mastoid portion.

Articulations. These are usually five in number, as follows: posteriorly and internally with the occipital, superiorly with the parietal, anteriorly with the sphenoid and zygomatic; and externally with the condyloid process of the mandible, the latter being a movable articulation. Sometimes the temporal articulates with the frontal, giving rise to a fronto-squamosal suture.

Structure. —The squamous portion is thin, and is practically composed of two plates of compact bone. The mastoid portion is thick, and, as stated, contains the tympanic antrum and mastoid air cells. The petrous portion is remarkable for its hardness, and it contains all the divisions of the organ of hearing, except the cartilage of the auricle on the outer side of the head. Thus it contains (1) the osseous external auditory meatus; (2) the tympanic cavity or middle ear, with its three ossicles, malleus, incus, and stapes, etc.; and (3) the osseous labyrinth or internal ear, which contains the membranous labyrinth, consisting of the utricle, saccule, semicircular canals, and membranous cochlea. It also contains, for a certain distance, extensions of the mastoid air cells.

Varieties. —(1) Persistence of foramen of Hiischke in the tympanic plate, due to imperfect ossification. (2) Obliteration of petro-squamous suture.

(3) Styloid process may be unusually long, or even united to the hyoid bone.

(4) Styloid process may be ununited by bone to the rest of the skull.

Ossification. — The temporal bone is developed in four parts, squamosal

or squamo-zygomatic, tympanic, petrosal, and hyal. The squamosal and tympanic elements are formed in membrane, and the petrosal in cartilage. The squamosal gives rise to the squamo-zygomatic portion, and the upper and front part of the mastoid portion; the tympanic forms the tympanic ring, and from the petrosal are developed the petrous portion and the greater part of the mastoid portion, while from the hyal the styloid process is derived. It is to be noted that the mastoid portion is not an independent part developmentally, but belongs chiefly to the petrous and partly to the squamosal portions. The centre for the squamosal appears towards the end of the second month of intra-uterine life in the region of the root of the zygomatic process, and from this ossification extends upwards into the squamosal, forwards into the zygoma, and inwards into the mandibular fossa in front of the squamo-tympanic fissure. From the posterior part of the squamosal a downward growth of bone takes place below the supramastoid crest, called the postauditory process, which forms the outer wall of the tympanic antrum, and gives rise to the upper and front part of the mastoid portion. Its hinder edge sometimes forms a fissure. The centre for the tympanic element appears towards the end of the third month of intrauterine life in the lower part of the external membranous wall of the tympanic cavity, and from this is developed the tympanic ring. This ring forms about five-sixths of a circle, the deficiency being above, where it is closed by the squamosal, and within the circumference of the ring there is a groove for the tympanic membrane. Previous to birth the extremities of the ring become ankylosed to the squamosal, and the tympanic plate is formed by an outward growth from it, so that it is ultimately located at the deep end of the external auditory meatus. The petrosal element or periotic cartilaginous capsule is developed from four centres, which appear towards the end of the fifth month, and from which ossification proceeds rapidly, union between the four centres being effected by the end of the sixth month of intra-uterine life. These centres are called opisthotic, pro-otic, pterotic, and epiotic, in the order of their appearance. The opisthotic centre appears on the promontory on the inner wall of the tympanic cavity, from which point ossification extends downwards around the fenestra cochlea, and forms (1) the floor of the vestibule, (2) the lower part of the fenestra vestibuli, (3) the floor of the internal auditory meatus, (4) the greater part of the bony investment of the cochlea, (5) the carotid canal, and (6) the floor of the tympanic cavity. The pro-otic centre appears near the inner limb of the superior semicircular canal in the region of the arcuate eminence, and from it are formed (1) the bony investment of the superior semicircular canal, (2) the roof of the vestibule, (3) the roof of the cochlea, (4) the roof of the internal auditory meatus, (5) the upper part of the fenestra vestibuli, and (6) the upper and inner part of the mastoid portion. The pterotic centre appears over the outer limb of the lateral semicircular canal, and from it are formed (1) the covering of the lateral semicircular canal, and (2) the tegmen tympani. The epiotic centre, sometimes double, appears in the region of the back part



Fig. 129. — The Temporal Bone in Early Life.

A, squamo-zygomatic portion and tympanic ring; B, petrosal portion* C the

bone at birth.

of the posterior semicircular canal, and from it the lower part of the mastoid is formed, as well as the investment of the posterior semicircular canal At the period of birth (the tympanic having previously joined the squamosal) the ° n a com P? sed ° f two parts: (1) a united squamo-zygomatic and • ^ fu" 1 1C< aiic i 2 ) a Pptrosal, a plate of cartilage intervening, and these unite

m,!+ h ^ COUrS c ° f y* ar - At birth the bone is of loose consistence, the

mastoid portion is flat, the external auditory meatus is undeveloped the

K™ Pa S! C rmg j ll r d i tympanic membrane are on a level with the exterior of the

aTavFvU?cl ndlbula L J 1 1 i §ular f o ssae are shallow, the parafloccular fossa is a cavity large enough to hold a small pea, and the hiatus for greater superficial


petrosal nerve is an open groove. The tympanic plate now becomes formed in fibrous tissue by the extension of osseous matter outwards from two tubercles on the anterior and posterior parts of the outer aspect of the tympanic ring superiorly. As these tubercles grow, they meet and enclose an opening in the floor of the external auditory meatus, which usually becomes closed about the seventh year, but may persist throughout life as the foramen of Hiischke. The tympanic antrum is present at birth, and is of large proportionate size, its outer wall being very thin. The mastoid process becomes developed in the course of the second year, and the antrum becomes relatively smaller, its outer wall at the same time becoming thicker. The mastoid air cells do not grow rapidly until the approach of the period of puberty.

Styloid Process. —This process has two centres of ossification, one for the tympano-hyal or basal part appearing before birth, which soon joins the rest of the bone, and the other for the stylo-hyal appearing in the first or second year. The latter portion is not well developed until after puberty, and its union with the tympano-hyal usually takes place in adult life, but it often remains separate.


The Sphenoid Bone

The sphenoid bone is so named from the wedge-like position which it occupies in the base of the skull, where it lies with its long axis placed transversely. It enters into the formation of the anterior, middle, and posterior fossae of the base, the temporal and nasal fossae, and the orbits. It consists of a central portion or body, two greater wings, two lesser wings, and two pterygoid processes.

The body presents six surfaces—superior, inferior, anterior, posterior, and two lateral, one at either side. Within the body are two large cavities, called the sphenoidal air sinuses, each of which opens on the anterior surface by a small circular aperture.

The superior surface presents at its centre a depression, called the sella turcica or hypophyseal fossa, for the hypophysis cerebri , and in the foetus it is pierced by the superior opening of the cranio-pharyngeal canal. In front of the sella turcica is the tuberculum sellae, which indicates the place of junction of the presphenoid and postsphenoid portions, and anterior to this is a transverse furrow, which, though called the optic groove, really lodges the anterior part of the circular sinus. The groove leads at either side to the optic foramen, by which the optic nerve leaves the cranial cavity, and anteriorly it is limited by a transverse ridge, called the limbus sphenoidalis. In front of the limbus (border) is a smooth elevated platform, called the jugum sphenoidale, which is continuous laterally with the superior surface of the lesser wing, and presents at either side the olfactory groove for the olfactory tract. The anterior border or the jugum is projected in the middle line into the ethmoidal spine, which articulates with the posterior margin of the cribriform plate of the ethmoid. The sella turcica is bounded posteriorly by a prominent quadrilateral plate of bone, called the dorsum sellse or dorsum ephippii (back of the saddle), which is directed forwards and upwards. The antero-inferior surface of this plate overhangs the sella turcica, and the postero-superior surface, called the clivus (slope), is inclined downwards and backwards to become continuous with the basilar groove of the occipital. The clivus lodges the upper part of the pons and the basilar artery. The antero-superior border of the dorsum sellae presents at either side the posterior clinoid process for a portion of the tentorium cerebelli and the interclinoid ligament, which latter connects it with the anterior clinoid process, and is sometimes ossified. On each lateral border of the dorsum sellae, a little below the posterior clinoid process, is a notch, which is often said to transmit the sixth nerve, but is really made by the inferior petrosal sinus. At the lower end of each lateral border there is a projection, called the posterior petrosal process, which articulates with the apex of the petrous portion of the temporal, and bounds medially the foramen lacerum.


Fig. 130. — The Sphenoid Bone (Superior View).


The inferior surface of the body is limited at either side by the medial pterygoid plate of the pterygoid process. In the middle line it presents a vertical, antero-posterior ridge, called the rostrum, which is continuous with the sphenoidal crest on the anterior surface, and is received into the cleft between the alse of the vomer. At either side

°l rostrum there is a thin scale of bone projecting inwards for a s ort distance from the root of the internal pterygoid plate, called the vaginal process, which articulates with the ala on the upper border °r e vomer, an< ? with it covers the greater part of the inferior surface °r 0 y at either side of the middle line. On the inferior surface is process there is a groove, which is converted by the sphenoidal process of the palatine bone into a canal, called the palatino-vaginal canal, for the passage of the pharyngeal nerve and corresponding vessels.

The anterior surface presents in the middle line a vertical ridge, continuous above with the ethmoidal spine and below with the rostrum, called the sphenoidal crest, which articulates with the perpendicular plate of the ethmoid and forms part of the nasal septum. On either side of this crest the surface is divided into two parts, outer and inner. The outer part is rough and often cellular to complete the posterior ethmoidal air cells and to articulate with the orbital process of the palatine bone. These cells are sometimes called the sphenoidal air


Fig. 131.—The Sphenoid Bone (Anterior View).


cells to distinguish them from the sphenoidal air sinuses into which they do not open. The inner part presents the opening of the sphenoidal air sinus of its own side, with the margins of which the sphenoidal concha or spongy bone articulates. When this bone is in position the opening of the sinus is small and circular, and is placed superiorly, but when the bone has been removed the opening is of large size and irregular outline. It communicates anteriorly with the sphenoethmoidal recess of the nasal fossa above and behind the superior meatus. The part of the anterior surface which presents the opening of the sphenoidal air sinus enters into the formation of the roof of the corresponding nasal fossa.


The posterior surface is rough and truncated. It articulates with the basilar process of the occipital by synchondrosis up to the twentieth year, after which ankylosis takes place.

The lateral surface gives attachment to the greater wing and a portion of the lesser wing. Anteriorly, beneath the lesser wing, it forms the inner boundary of the sphenoidal fissure and the back part of the inner wall of the orbit. Above the attachment of the greater wing it presents a winding groove, called the carotid groove, which contains the cavernous venous sinus and the internal carotid artery. The direction of this groove is from behind forwards, and its deepest part is placed posteriorly, where it is bounded internally by the posterior petrosal process, and externally by the lingula of sphenoid or anterior petrosal process. This latter process is a sharp scale of bone which projects backwards in the angle between the greater wing and body, fitting close against the outer side of the internal carotid artery where it is running upwards after leaving the carotid canal in the temporal bone.

The lesser or orbital wings (orbito-sphenoids) extend almost horizontally outwards on a level with the anterior part of the upper surface of the body. Each arises by two roots—an upper, which is expanded and compressed from above downwards, and is on a level with the anterior part of the upper surface of the body; and a lower, slender and compressed from before backwards, which arises from the anterior part of the side of the body. The wing is triangular and flattened from above downwards. The superior surface, smooth and somewhat concave, forms the back part of the anterior cranial fossa. The inferior surface overhangs the superior orbital fissure, and forms the back part of the roof of the orbit. Laterally the wing ends in a slender, pointed extremity, which lies very near the greater wing, but does not as a rule touch it, though it may do so. The anterior border is thin and serrated for the orbital plate of the frontal. The posterior border, .smooth, thick, and round, corresponds with the lateral sulcus (or Sylvian fissure) of the cerebrum, from which circumstance it is known as the Sylvian border. It forms at either side the line of demarcation between the anterior and middle cranial fossae, and terminates internally in the anterior clinoid process for a portion of the tentorium cerebelli and the interclinoid ligament.

Between the anterior clinoid process and the side of the olivary eminence is the semicircular carotid notch, which is the anterior termination of the carotid groove, and lodges the internal carotid artery.

On either side of the body, close to the inner side of the anterior extiemity of the carotid groove and posterior to the carotid notch, °PP°site the anterior clinoid process, there is usually a small tubercle, called the middle clinoid process. It is connected with the anterior clinoid piocess by the carotico-clinoid ligament, which bridges over the carotid notch. When this ligament undergoes ossification a carotico-clinoid foramen is formed, through which the internal carotid artery ascends after leaving the carotid groove.


In front of the carotid notch, between the upper and lower roots of the small wing, there is a circular aperture, called the optic foramen, which leads forwards and outwards into the orbit, and transmits the optic nerve and the ophthalmic artery.

The greater or temporal wings (alisphenoids) extend outwards, upwards, and forwards from the sides of the body. The posterior part of each projects backwards, and ends in a pointed extremity, which is received within the petro-squamous angle of the temporal bone. From this extremity a sharp projection extends downwards for a short distance, called the spine of sphenoid or alar spine, which often has a groove on its inner aspect for the chorda tympani nerve. Anterior to this groove, and encroaching on the posterior border of the greater wing, is another groove for the cartilaginous part of the pharyngo-tympanic tube. The spine of the sphenoid gives attachment to (i) the spheno-mandibular ligament, (2) some fibres of the tensor palati, and (3) the anterior ligament of the malleus.

Each greater wing presents three surfaces—superior, anterointernal, and external; and four borders—posterior, lateral, anterior, and medial.

The superior or cerebral surface , which at its front part rises almost vertically upwards, is concave, and enters into the formation of the lateral division of the middle cranial fossa. It supports the temporal lobe of the cerebrum, and presents a few digitate impressions, whilst laterally it is grooved for a branch of the middle meningeal artery. This surface presents several important foramina. At the anterior part of its attachment to the side of the body, just below the inner end of the superior orbital fissure, is the foramen rotundum, which is directed from behind forwards and transmits the maxillary division of the fifth cranial nerve. A little behind and lateral to this foramen is the foramen ovale, of large size and opening vertically downwards, for the passage of the mandibular division and the motor root of the fifth cranial nerve, the accessory meningeal artery, the middle meningeal vein, and sometimes the lesser superficial petrosal nerve. Medial and anterior to the foramen ovale, between it and the lingula sphenoidalis, there is sometimes a small opening, called the emissary sphenoidal foramen (foramen Vesalii), which leads to the scaphoid fossa on the outer side of the root of the medial pterygoid plate, or to the pterygoid fossa lateral to the scaphoid fossa. It transmits a small emissary vein from the cavernous sinus. Behind and external to the foramen ovale is the small circular foramen spinosum, close to the spine of the sphenoid, which opens vertically downwards. It transmits the middle meningeal artery and nervus spinosus branch of the mandibular nerve, and is sometimes incomplete posteriorly. Medial to this foramen, between it and the foramen ovale, there is sometimes a small opening, called the innominate canal, for the lesser superficial petrosal nerve.

The antero-medial surface is divisible into a large orbital portion and a small pterygo-palatine portion. The orbital division is quadrilateral, smooth, and slightly concave, and it forms the greater part of the outer wall of the orbit. The pterygo-palatine division is situated at the lower and inner part above the root of the pterygoid process. It is pierced by the foramen rotundum, and lies in the posterior wall of the pterygo-palatine fossa.

The lateral or temporo-zygomatic surface is elongated from above downwards, and is continuous with the outer surface of the lateral pterygoid plate of the pterygoid process. Towards its lower part it is crossed by the infratemporal crest, which divides it into a large upper and a small lower portion. The upper or temporal division, which is directed outwards, forms part of the temporal fossa, and gives origin to fibres of the temporal muscle. The lower or zygomatic division looks downwards into the infratemporal fossa, and gives origin to the upper head of the lateral pterygoid muscle. At its lower and back part are the openings of the foramen ovale and foramen spinosum.

The posterior border extends from the spine of sphenoid to the body, passing in its course behind the foramen ovale. Over its inner twothirds it bounds the foramen lacerum anteriorly, and over its outer third, where it becomes serrated, it articulates with the petrous portion of the temporal, the two forming a groove for the cartilaginous part of the pharyngo-tympanic tube. The lateral border separates the superior or cerebral from the lateral or temporo-zygomatic surface. It is serrated behind, where it is bevelled at the expense of the upper or inner plate, but in front it is squamous and bevelled at the expense of the outer plate.

is wor th calling attention here to the frequency with which this alternate bevelling is found in the skull bones, and how greatly it adds to the strength of the sutures. 6

The entire border articulates with the squamous portion of the temporal. The anterior border or zygomatic crest separates the orbital and temporal surfaces. Its direction is downwards and inwards, and it is sharp and irregular for the malar. The medial border is situated between the orbital and cerebral surfaces. Its direction is backwards a,nd inwards, and it forms the lower boundary of the superior orbital fissure. About its centre it presents a small spine, which gives origin to fibres of the lower head of the lateral rectus muscle of the eyeball. The greater wing antero-superiorly becomes thick and expanded, and it here presents a rough, triangular, serrated surface tor the frontal. At the outer end of this surface there is another small triangular, serrated impression for the antero-inferior angle of the parietal. °

The superior orbital fissure is situated between the greater and lesser wings. It is triangular, and its direction is inwards and downwards It is bounded above by the lesser wing, below by the medial border of the greater wing, and medially by the anterior part of the side of the body, whilst laterally it is closed by the frontal, ° r T may be i , the meeting between the two wings. It leads from the JiL c e crama l fossa to the orbit, and transmits the following structures:


the third cranial nerve, the fourth, the three branches of the ophthalmic division of the fifth (namely, frontal, lacrimal, and naso-ciliary), and the sixth cranial nerves, the sympathetic root of the ciliary ganglion, the superior ophthalmic veins, the orbital branch of the middle meningeal artery, and a portion of the dura mater to form the orbital periosteum.

The pterygoid processes project downwards from the junction of the body and greater wings. Each is composed of two plates, lateral and medial, united in front to form a thick round border, except interiorly, where they are separated by the pterygoid fissure, which receives the tubercle of the palatine bone. At the upper end of the anterior border a triangular surface opens out, which lies in the posterior wall of the pterygo-palatine fossa, and presents the anterior orifice of the pterygoid canal. Posteriorly the two plates diverge, and enclose between them the pterygoid fossa, which contains the medial pterygoid and tensor palati muscles.



Fig. 132.—The Sphenoid Bone (Posterior View).


The lateral pterygoid plate is broader and shorter than the medial, and is directed backwards and slightly outwards. Its outer surface looks into the zygomatic fossa, and gives origin to the lower head of the lateral pterygoid muscle. Its inner surface looks into the pterygoid fossa, and gives origin to the medial pterygoid muscle. The posterior border usually presents towards its upper part a sharp spine, from which the pterygo-spinous ligament extends backwards and outwards to the spine of the sphenoid. This ligament sometimes becomes ossified, and a foramen is then formed, called the pterygo-spinous foramen, for the passage of muscular branches of the mandibular nerve. Sometimes there is another spine towards the lower end of this border for another pterygo-spinous ligament.



The medial pterygoid plate, narrower and longer than the lateral, is prolonged interiorly into the pterygoid hamulus, which is inclined outward and backward, its outer and lower aspects being smooth and grooved for the play of the tendon of the tensor palati. Superiorly this plate is inflected as the vaginal process, which articulates with the ala of the vomer, and has on its under surface the groove, forming part of the greater palatine canal, already referred to. The outer surface of the medial pterygoid plate looks into the pterygoid fossa, and is related to the tensor palati. The inner surface forms the back part of the outer wall of the nasal fossa. The posterior border at its upper end presents the pterygoid tubercle, which has the posterior end of the pterygoid canal above and lateral to it. Between this tubercle and the pterygoid canal on the one hand, and the pterygoid fossa on the other, is the scaphoid fossa, which gives origin to the tensor palati. On the posterior border of the medial pterygoid plate, below the lower pointed end of the scaphoid fossa, is the processus tubarius, which supports the cartilage of the pharyngo-tympanic tube. The lower third of the posterior border and the pterygoid hamulus give origin to fibres of the superior constrictor muscle of the pharynx, and the pterygoid hamulus also gives attachment to the pterygomandibular ligament. The anterior border articulates with the posterior border of the perpendicular plate of the palate bone.

The pterygoid canal pierces the bone from before backwards at the junction of the internal pterygoid plate and body on either side. Its anterior orifice appears on the posterior wall of the pterygo-palatine fossa, below and internal to the anterior orifice of the foramen rotundum, and posteriorly it opens on the anterior wall of the foramen lacerum medium, above and lateral to the pterygoid tubercle. It gives passage to the nerve and artery of the pterygoid canal.

Summary of Openings in the Sphenoid Bone.—(i) Superior orbital fissure, between lesser and greater wings; (2) optic foramen, between the two roots of the lesser wing; and, in the greater wing, (3) foramen rotundum; (4) foramen ovale; (5) emissary sphenoidal foramen (inconstant) ; (6) foramen spinosum; (7) innominate canal (inconstant); and (8) pterygoid canal, the last-named being between the medial pterygoid plate and the body. All these openings are common to each side.

The sphenoidal air sinuses are situated within the body, and are two in number, right and left. They are separated from each other by a septum, which is seldom quite median and often incomplete. Ihe sinuses are—at least, after adult life—usually multilocular, and they may extend backwards so as to invade the basilar process of the occipital, especially in old age. Each sinus may even extend slightly into the attached portion of the greater wing. They are lined with mucous membrane, which is continuous with that of the nasal fossae, and each opens^ anteriorly by a small circular aperture into the spheno-ethmoidai recess above and behind the corresponding superior meatus.


The sphenoidal conchae are situated on the anterior and inferior surfaces of the body of the sphenoid, of which they form a large part. In the adult they are blended with the sphenoid and adjacent parts of the ethmoid and palatine bones, but in early life they are quite distinct. Each has the form of a three-sided, hollow pyramid, the apex of which is directed backwards and downwards to the front part of the vaginal process, whilst the base is in contact with the back part of the labyrinth of the ethmoid. The inferior surface looks into the posterior part of the roof of the nasal fossa, and it converts the spheno-palatine notch on the upper border of the perpendicular plate of the palatine bone into a foramen. The lateral surface appears on the inner wall of the pterygo-palatine fossa, and a portion of it is sometimes seen on the inner wall of the orbit, behind the orbital plate of the ethmoid. The superior surface is in contact with the anterior and inferior surfaces of the front part of the body of the sphenoid. It is at the upper part of this surface, on either side of the middle line, that the openings of the sphenoidal air sinuses ultimately appear as small oval apertures. When the sphenoidal conchae are broken away these openings are of large size and irregular outline.

The blood-supply of the bone is derived from branches of the deep temporal arteries externally, the middle and accessory meningeal internally, and the artery of pterygoid canal, greater palatine, and spheno-palatine branches of the maxillary, as these traverse their respective passages.

Articulations.—The sphenoid articulates with fourteen bones as follows: occipital, two temporals, two parietals, frontal, ethmoid, two sphenoidal conchae, two zygomatics, two palatines, and vomer. It sometimes also articulates with the maxillae.

Structure. — The body of the bone is excavated into two air sinuses.

Varieties. — (1) Middle clinoid process. (2) Carotico - clinoid foramen. (3) Ossification of interclinoid ligament between anterior and posterior clinoid processes. (4) The lateral margin of the dorsum sellae may present a superior petrosal process for the attachment of the petro-sphenoidal ligament, which connects it with a projection sometimes present on the inner part of the superior border of the petrous portion of the temporal. This ligament, which is sometimes ossified, bridges over a foramen through which the inferior petrosal venous sinus and sixth cranial nerve pass. (5) Pterygo-spinous foramen. (6) Foramen ovale and foramen spinosum are sometimes incomplete. (7) Emissary sphenoidal foramen. (8) Innominate canal. (9) The cranio-pharyngeal canal may remain persistent, opening into the hypophyseal fossa. (10) The dorsum sellae may be joined to the rest of the bone by membrane only.

Ossification. —The sphenoid is developed in cartilage, with the exception of the medial pterygoid plates, which are developed in fibrous tissue.* The bone is originally divided into two parts—presphenoid, representing the part of the body in front of the tuberculum sellae, and the lesser wings; and postsphenoid, including the part of the body behind the tuberculum sellae, the greater wings, and the pterygoid processes. The postsphenoid division is developed from


According to recent observations made by Fawcett, the lateral pterygoid plates are also developed in fibrous tissue.



four pairs of centres. One pair appear in the eighth week of intra-uterine life, one at either side in the greater wing between the foramen rotundum and foramen ovale, and from this ossification extends outwards into the greater wing and downwards into the lateral pterygoid plate. Another pair appear about the same time in the sella turcica on either side of the cranio-pharyngeal canal, from which ossification extends around the canal, gradually constricting it, and finally leading to its closure. At this time another pair (sphenotics of Bland-Sutton) appear, one at each side, for the lingula. In the fourth month (ninth or tenth week, Fawcett) another pair of centres appear in fibrous tissue, one at either side, for the medial pterygoid plate, which unites with the lateral pterygoid plate before the sixth month. The presphenoid division is developed from two pairs of centres. Two appear in the ninth week, one at either side, lateral to the optic foramen, for the lesser wing. Another pair appear in the eleventh week medial to the optic foramina for the presphenoid portion of the body. The latter pair soon unite with each other, and also with those for the lesser wings. The presphenoid division, bearing the lesser wings, joins the postsphenoid division shortly before birth in the region of the tuberculum sellae.


Fig. 133. — The Sphenoid Bone in Early Life.

I, presphenoid division; II, postsphenoid portion of body; III, greater wing and pterygoid process; IV, elements of pterygoid process.

At birth the place of junction is indicated by a wide depression on the under aspect of that eminence, which may even extend through it and give rise to a small foramen on its upper surface.

At birth the bone is composed of three parts—a central, representing the presphenoid and postsphenoid portions of the body, the former bearing the lesser wings; and two lateral, each of which represents a greater wing bearing a pterygoid process. In the first year the lingula joins the greater wing, and the wing and body unite. About the same time the lesser wings come together and blend over the anterior part of the upper surface of the presphenoid portion of the body, where they give rise to a smooth, elevated, flat platform, called the jugum sphenoidale.

In foetal life a canal, called the cranio-pharyngeal canal, leads downwards Lorn the sella turcica into the body, and contains a process of the dura mater. 4 y lls °anal is the remains of a cleft originally present in the base of the skull, t> cui 1 w . . diverticulum of the buccal ectoderm, known as the pouch of Kathke, originally passed upwards to form the anterior lobe of the hypophysis Cere ^ n ‘ ^ uch a communi cation through the base of the skull, in the mid-line, could not have occurred farther back, because the anterior end of the notochord corresponds m position with the dorsum sellae.


The sphenoidal air sinuses begin to invade the bone by the fifth year.

In most animals the presphenoid and postsphenoid portions remain permanently separate, and the medial pterygoid plates form the pterygoid bones.

The sphenoidal conchse commence to ossify in the fifth month of intra-uterine life. At birth each partially envelops a small extension of the nasal mucous membrane, and by the third year it has surrounded it in the form of a bony capsule, except anteriorly, where an opening, called the sphenoidal foramen, is left. Subsequently a portion of this capsule becomes absorbed, and its place is taken by the presphenoid, which latter, after the seventh year, is gradually invaded by the original extension of the nasal mucous membrane. The sphenoidal conchae become ankylosed to the ethmoid about the fourth year, and are sometimes regarded as belonging to that bone. By the twelfth year they have become united to the sphenoid and also to the palatine bones.


The Ethmoid Bone

The ethmoid bone is situated at the anterior part of the base of the skull, where it lies in the middle line in front of the sphenoid. A portion of it occupies the ethmoidal notch between the orbital plates of the frontal, whence the greater part of the bone projects downwards, to take part in the formation of the orbits and nasal fossae. The only portions of the bone visible in the interior of the base are the cribriform plate and crista galli. It is irregularly cubical, its long axis being directed from before backwards, and it is remarkable for its lightness, which is due to the great number of enclosed air cells, these being surrounded by very thin plates of bone. It is composed of four parts—namely, a cribriform plate, a perpendicular plate, and two ethmoidal labyrinths.

The cribriform plate connects the upper borders of the labyrinths, and enters into the formation of the middle division of the anterior cranial fossa, where it occupies the ethmoidal notch of the frontal bone. In the middle line anteriorly it presents an upward extension of the perpendicular plate, called the crista galli. This is a stout, triangular, laterally-compressed process, which has a smooth, sloping posterior border, for the falx cerebri. The anterior border, short and vertical, is somewhat narrow above, but soon expands into two alse, for the frontal bone, and it here sometimes completes the foramen caecum. The posterior border is prolonged backwards as a median ridge, and on either side of this ridge and the crista galli is the olfactory groove, which lodges the olfactory tract and bulb. Each half of the cribriform plate, which lies in the roof of the corresponding nasal fossa, is pierced by foramina for the filaments of the olfactory bulb. The foramina in each half are arranged in three sets as follows: a middle set, which are simple perforations, and a medial and lateral set, which lead into small canals. These canals descend on the perpendicular plate and inner surface of the ethmoidal labyrinth respectively, branching and opening out as they descend. All the foramina lead to the upper part of the corresponding nasal fossa. At the anterior and inner part of each half of the cribriform plate, close to the side of the crista galli, near its anterior border, there is an antero-posterior fissure, called the nasal slit, which transmits the nasal branch of the anterior ethmoidal artery to the nasal fossa, while a small foramen just in front and to the outer side of it is for the nasal nerve. Leading backwards and outwards from this foramen to the anterior ethmoidal groove on the upper border of the labyrinth is the nasal groove, also for the anterior ethmoidal nerve. The posterior border of the cribriform plate articulates with the ethmoidal spine of the sphenoid.

The perpendicular plate (mesethmoid) extends downwards from the cribriform plate in the middle line. It lies between the labyrinths, where it forms about the upper third of the nasal septum, and it is usually inclined more to one side than the other. It is very thin and irregularly pentagonal. The superior border projects above the cribriform plate and forms the crista galli. The antero-infericr border articulates with the septal cartilage of the nose, the postero-inferior with the alae of the vomer in the intervening cleft, with which alae it is usually ankylosed in adult life. The anterior border articulates with the nasal spine of the frontal and the nasal crest of the nasal bones. Ih e posterior border articulates with the crest of the sphenoid. Each lateral surface looks into the corresponding nasal fossa, and presents superiorly several small canals and grooves, which lead downwards from the medial set of foramina in each half of the cribriform plate, and transmit olfactory filaments.


Fig. 134.— The Ethmoid Bone (Superior View).



The ethmoidal labyrinths (lateral masses) form the principal part of the bone, and contain a number of air cells enclosed within very thin osseous plates. Each labyrinth is elongated from before backwards, and presents two surfaces and four borders.

The lateral surface, smooth and quadrilateral, with the long axis directed from before backwards, is called the orbital plate (os planum), and forms the principal part of the inner wall of the orbit. It articulates superiorly with the inner border of the orbital plate of the frontal, anteriorly with the lacrimal, inferiorly with the inner margin of the orbital plate of the maxilla, and behind this with the orbital process of the palatine bone, close to the postero-inferior angle, and posteriorly with the sphenoid, or, it may be, with a portion of the sphenoidal concha. At the lower part of the lateral surface, below the orbital plate, there is a deep channel, elongated from before backwards, which forms the middle meatus of the nose, and is limited below by the inferior rolled border of the middle nasal concha. This groove turns upwards in front, under cover of the anterior part of the middle nasal concha, and is continued into the infundibulum which communicates with the frontal sinus of the same side. The anterior ethmoidal sinus opens into the ascending part of the middle meatus, whilst the middle ethmoidal sinus and the maxillary sinus open into its horizontal part. Lying in the anterior part of this meatus is the uncinate process.



Fig. 135. — The Ethmoid Bone (Lateral View).


The medial surface of the labyrinth forms a part of the outer wall of the nasal fossa. Superiorly it has several small canals and grooves which lead downwards from the lateral set of foramina in the cribriform plate and transmit olfactory filaments. This surface is doubly convoluted, and presents the superior and middle nasal conchae, which are sometimes spoken of as the superior and middle spongy bones. These are continuous with each other in front, but posteriorly they are separated by the superior meatus, which is directed obliquely forwards and upwards, and communicates with the posterior ethmoidal sinus or sinuses. The superior nasal concha is short, and overhangs the superior meatus. The middle nasal concha is longer and more convoluted than the superior. Its lower border, which is thick, is rolled outwards, and has been referred to in connection with the outer surface. It is free, as are also its thick anterior and pointed posterior extremities. This process overhangs the middle meatus. Both conchas are pierced by nutrient foramina, and present grooves for olfactory filaments.


The superior border is covered by the bevelled inner margin of the orbital plate of the frontal, which closes in the depressions upon it, and converts them into sinuses. Besides these depressions this border presents two transverse grooves about \ inch apart, which, with corresponding grooves on the orbital plate of the frontal, form the anterior and posterior ethmoidal foramina. These open upon the inner wall of the orbit, and the anterior transmits the anterior ethmoidal vessels and nerve, whilst the posterior gives passage to the posterior ethmoidal vessels and nerve. The inferior border, which is free on the outer wall of the nasal fossa, is formed by the lower border of the middle nasal concha. Anteriorly it articulates with the superior turbinate crest of the maxilla, and posteriorly with the ethmoidal or superior turbinate crest of the palatine bone. The anterior border, like the superior, presents depressions, which form sinuses when the lacrimal and nasal process of the maxilla are in position. This border projects slightly in advance of the front of the orbital plate (of ethmoid), and from the lower part of this projecting portion there springs the uncinate process. This is a long, thin, curved plate which extends downwards, backwards, and slightly outwards into the anterior part of the middle meatus. In its course it crosses the opening of the maxillary sinus in the maxilla, and thus forms part of the inner wall of that sinus. The lower border of the process presents two spur-like projections, between which the border is markedly concave. The posterior terminal spur articulates with the ethmoidal process of the inferior nasal concha. The posterior border of the lateral mass presents a few depressions, closed by the sphenoidal concha and orbital process of the palatine bone, which latter process becomes ankylosed with it about the fourth year.



Fig. 136. — The Left Lateral Mass of the Ethmoid Bone (Internal View).


The ethmoidal sinuses are contained within each labyrinth, and are lined with mucous membrane, which is continuous with that of the nose. They are arranged in three sets—anterior, middle, and posterior. The anterior ethmoidal sinuses, along with the frontal sinus of the same side, open by a common passage, already described as the infundibulum, into the ascending front part of the middle meatus; the middle ethmoidal sinus opens into the horizontal part of the middle meatus; and the posterior ethmoidal sinus opens into the superior meatus.

The bone receives its blood-supply from the anterior and posterior ethmoidal branches of the ophthalmic, and the spheno-palatine branch of the maxillary.

Articulations. — The ethmoid articulates with fifteen bones as follows: (i) frontal (nasal spine and orbital plates); (2) sphenoid (ethmoidal spine and sphenoidal crest); (3) two sphenoidal conchae; (4) two nasal bones (nasal crest); (5) vomer (cleft between alas); (6) two palatine bones (ethmoidal or superior turbinate crests and orbital processes); (7) two lacrimals (upper part of internal surface); (8) two maxillae (nasal processes, orbital plates, and opening of each maxillary sinus) ; and (9) two inferior nasal conchae (ethmoidal processes).

Structure. — The labyrinths are excavated into many thin-walled air cells, and the crista galli contains a small amount of cancellated tissue.

Ossification. — The ethmoid is developed in cartilage from three centres. Two of these appear in the fifth month of intra-uterine life, one in each orbital plate, from which ossification extends into the superior and middle nasal conchae. At birth the labyrinths are ossified, but the perpendicular plate and crista galli are cartilaginous. In th q first year a centre appears at the base of the crista galli, and from this ossification extends upwards into that process, downwards into the perpendicular plate, and outwards into the cribriform plate, into which latter osseous matter also extends inwards from each labyrinth. The three original parts unite about the fifth year. The osseous ethmoidal sinuses usually make their appearance about the third year.


The Maxillae

The maxilla forms, with its fellow, a large part of the face, and, besides supporting the upper teeth of its own side, it enters into the formation of the orbit, nasal fossa, and hard palate. It is composed of a central portion or body, and four processes—frontal, zygomatic, alveolar, and palatine.

The body is excavated into a large cavity, called the maxillary sinus, and it presents four surfaces—anterior, posterior, orbital, and nasal.

The anterior or facial surface is limited above by the infra-orbital border, below by the alveolar border, medially by the medial border, presenting the nasal notch, and laterally by the zygomatic process and a ridge of bone extending downwards from it to the first molar alveolus. It presents inferiorly five ridges, coinciding with the roots of the incisor, canine, and premolar teeth, of which that of the canine is conspicuous, and is called the canine ridge. Medial to this ridge is the incisive fossa, which gives origin medially to the depressor septi, and externally to a deep slip of the orbicularis oris, whilst above, and lateral to, the latter the compressor naris arises. Lateral to the canine ridge is the canine fossa, which, at its upper part, gives origin to the levator anguli oris, the bone being here thin and translucent in front of the maxillary sinus. Above the canine fossa, near the infra-orbital border, is the infra-orbital foramen, which is the outlet of the infra-orbital canal, and transmits the infra-orbital nerve and vessels. Immediately above this foramen the levator labii superioris arises. The medial border of the facial surface presents the deep nasal notch, at the lower and inner part of which is a sharp projection, forming, with its fellow, the anterior nasal spine, below which the border is vertical.


Fig. 137. — The Right Maxilla (Lateral Aspect),



The posterior or zygomatic surface is situated behind the zygomatic process and the ridge connecting that process with the first molar socket. Superiorly it is limited by the posterior border of the orbital surface, interiorly by the molar portion of the alveolar arch, and posteriorly by the posterior border of the bone. It looks into the zygomatic and pterygo-palatine fossae, and its outline is convex. Towards the centre it presents the openings of two or three posterior dental canals, which lead to the molar sockets, and transmits branches of the posterior superior dental nerve and artery. At the lower and back part this surface gives rise to the tuberosity, which lies above and behind the last molar tooth. This tuberosity articulates with the tubercle of the palatine bone, and gives origin to some fibres of the medial pterygoid muscle.

The superior or orbital surface is triangular, smooth, and slightly concave, and it forms the greater part of the floor of the orbit. This portion of the bone is known as the orbital plate. It presents the infra-orbital groove, which at first runs outwards, slightly grooving the bone just behind the orbital plate; this leads, at the middle of the posterior border of the plate, into a well-marked groove which runs forwards and ultimately becomes converted into the infra-orbital canal. This canal transmits the infra-orbital nerve and vessels. From its posterior part the middle dental canal, for the middle superior dental nerve and a branch from the posterior superior dental artery, passes downwards and forwards to the premolar sockets, lying at first in the postero-lateral wall of the maxillary sinus, and subsequently in the antero-lateral wall. The canal is often for the most part a groove. The anterior dental canal, for the anterior superior dental nerve and artery, descends in a branching manner from the anterior part of the infra-orbital canal to the incisor and canine sockets, lying in the antero-lateral wall of the sinus. At the anterior and inner part of the orbital plate, lateral to the nasolacrimal groove, there is a slight depression which gives origin to the inferior oblique muscle of the eyeball. The borders of the orbital surface are anterior, posterior, and medial. The anterior border coincides with the infra-orbital border. The posterior border, which has an inclination outwards, forms the anterior boundary of the inferior orbital fissure, and presents a notch which is the beginning of the infra-orbital groove. The medial border, antero-posterior in direction, presents, behind the nasal process, the lacrimal notch for the lacrimal bone, and behind this it articulates from before backwards, with the lower border of the orbital plate of the ethmoid and the orbital process of the palatine bone. This border presents a few depressions which close in ethmoidal sinuses.

The nasal surface forms part of the outer wall of the nasal fossa. It is limited in front by the medial border of the bone, behind by the posterior border, above by the medial border of the orbital surface, and below for the most part by the palatine process. It presents the opening of the maxillary sinus, in front of which is the deep lacrimal groove, directed downwards, outwards, and backwards, and, after a course of about \ inch, opening into the front part of the inferior meatus of the nose. This groove is converted posteriorly and medially into the lacrimal canal by the lacrimal and inferior nasal concha bones, and it transmits the naso-lacrimal duct. In front of the lacrimal groove is a slightly oblique ridge, called the conchal crest, for articulation with the inferior nasal concha, and below this is a smooth concave surface which forms the anterior part of the inferior meatus. Above the crest is the commencement of another smooth surface, which extends upwards on to the inner aspect of the frontal process, and forms the outer wall of the atrium of the middle meatus. Behind the opening of the maxillary sinus the internal surface articulates with the perpendicular plate of the palatine bone, and it presents, from the centre downwards, a groove, directed downwards and forwards, which, with the palatine bone, forms the greater palatine canal for the greater palatine nerve and vessels. Above the opening of the sinus are a few depressions on the medial border of the orbital surface, forming ethmoidal sinuses.

The frontal process ascends vertically from the medial part of the facial surface above the nasal notch. It is somewhat triangular, and presents two surfaces and three borders. The lateral surface is continuous with the facial surface of the body, and gives attachment to the orbicularis oculi, medial palpebral ligament, and levator labii superioris alaeque nasi. It will be noticed that the lower margin of the orbit is continued up on to this surface, and that, behind it, is a groove which lodges part of the lacrimal sac. The medial surface forms part of the outer wall of the nasal fossa, and, at its back part superiorly, it presents one or two depressions, completing cells on the anterior border of the labyrinth of the ethmoid. The surface is crossed obliquely backwards and upwards by a ridge, called the agger nasi, which represents an additional nasal concha present in most mammals. This crest bounds superiorly the atrium of the middle meatus, and articulates posteriorly with the anterior extremity of the middle nasal concha of the ethmoid. Above the agger nasi there is a groove, called the sulcus olfactorius. The superior border is short, thick, and serrated for the frontal. The anterior border is sharp and articulates with the nasal.

The zygomatic process is stout and triangular. Its anterior surface is continuous with the facial surface of the body, and its posterior with the zygomatic surface, whilst the superior surface is rough and slightly serrated for the zygomatic bone.

The alveolar process forms the dependent part of the bone, and is thick and curved, being convex laterally and concave medially. The outer plate is known as the labial plate, and the inner as the lingual. 1 he two plates are widely separated, and the intervening space is partitioned off into sockets by septa which pass between the two plates. The number of sockets in the adult bone is as a rule eight, and they gradually narrow towards their upper or deep ends, where they are perforated by foramina for the nerves and arteries of the teeth. They lodge the roots of the teeth, which, in order from the middle line outwards and backwards, are as follows: central incisor, lateral incisor, canine, first premolar, second premolar, and first, second, and third molars.. The sockets correspond in shape with the roots of the teeth, the canine being the deepest. The outer surface of the alveolar border, over the extent of the three molar sockets, gives origin to fibres of the buccinator.


It should be remembered that the presence of an empty socket shows that the tooth has fallen out after death. When a tooth is lost during life the socket is absorbed. Carious teeth are less likely to fall out post-mortem than sound ones.

The palatine process is situated on the medial surface of the body, from which it projects horizontally inwards, and, with its fellow, it forms three-fourths of the hard palate. It is quadrilateral, and presents two surfaces and four borders. The superior surface forms threefourths of the floor of the nasal fossa, and is smooth, concave, and covered in the recent state by the nasal mucous membrane. The inferior surface forms a part of the hard palate, and is rough, arched, and covered in the recent state by the buccal mucous membrane. It presents several depressions for the palatine mucous glands, and is perforated by several nutrient foramina. Laterally it is marked by a groove, directed from behind forwards, for the nerve and artery which reach the hard palate through the greater palatine canal. The posterior border stops short of the back part of the alveolar arch, and is short and serrated for the horizontal plate of the palatine bone. The anterior border, superiorly, forms the lower part of the nasal notch. The lateral border is attached to the body. The medial border is faintly serrated, and articulates with its fellow. At the place of meeting it is elevated into a ridge, forming, with that of its fellow, the nasal crest, which is grooved to receive the lower border of the vomer. This medial ridge becomes prominent in front, where it forms the incisor crest, which is projected to constitute, with its fellow, the anterior nasal spine. It supports the septal nasal cartilage, and the anterior extremity of the vomer lies behind it.



Fig. 138. — The Right Maxilla (Medial Aspect).



Close to the outer side of the incisor crest the palatine process is pierced by an opening leading into a canal, which is bounded medially by a thin plate of bone, and descends to the front part of the hard palate, being ultimately converted into a groove, due to its inner thin wall becoming deficient. This passage is known as the incisive canal, and the two canals, right and left, in the articulated condition form interiorly a large orifice, called the incisive fossa. This fossa, which is somewhat diamond-shaped, is situated in the middle line of the hard palate, behind the central incisor teeth. On looking into it from below four foramina are seen, two of which are placed in the middle line, where they lie in the intermaxillary suture. These are known as the median incisive foramina, and they transmit the long spheno-palatine nerves, the left nerve passing through the anterior, which usually communicates with the left nasal fossa, and the right through the posterior, which usually communicates with the right nasal fossa. The other two foramina are situated one at either side, and are known as the lateral incisive foramina, and the canal into which each leads opens superiorly on the floor of the corresponding nasal fossa, close to the outer side of the incisor crest. Each lateral incisive foramen transmits a branch of the greater palatine artery from the incisive fossa to the nasal fossa. The inner wall of Stensen’s canal, on each side, represents the medial palatal process of the premaxilla or intermaxillary bone, and also a portion developed from the prepalatine centre. The lateral incisive canals correspond to the incisor foramina of many animals— e.g., the ruminants, in which they are of large size, and each opens independently on the front part of the hard palate as a large aperture, there being no incisive fossa. In such animals each incisive foramen leads up to the orifice of the vomero-nasal organ, which is a supplementary organ of smell. In man the incisive canals are the remains of a communication which existed in early foetal life between the nasal and buccal cavities.

Passing transversely outwards from the incisive fossa at its back part to the interval between the lateral incisor and canine teeth a suture E always present in early life, and may persist in the adult, which is said to indicate the line of junction of the maxillary portion proper and the premaxilla or intermaxillary bone, the latter representing txie part which bears the central and lateral incisor teeth. This intermaxillary portion forms an independent bone in many animals. Sometimes a rough, antero-posterior elevation is seen in the mid-line, benind the incisive fossa, known as the torus palatinus. It may be mistaken for a bony tumour or exostosis.


The maxillary sinus is situated within the body of the bone, and is of large size, its capacity in health being equal to about 2 drachms. It has the shape of a four-sided pyramid, and is lined with mucous membrane continuous with that of the nasal fossa. The apex corresponds to the zygomatic process, and the base represents the nasal aspect. The superior wall or roof is formed by the orbital plate. The inferior wall or floor is formed by that portion of the alveolar border which contains the molar and second premolar sockets, and, in some cases, the first premolar socket also. It is often very irregular, due to projections of the upper ends of the sockets, and in some cases the root of the first molar, and, it may be, that of the second, projects into the antral cavity. The antero-lateral wall is formed by the facial surface, and is thin and translucent over the region of the canine fossa. It contains the anterior, and the lower part of the middle, dental canals. The postero-lateral wall is formed by the zygomatic surface, and it contains the upper part of the middle dental canal. The opening of the sinus, which is large and irregular, is situated on the base or nasal aspect. In the articulated skull its size is considerably diminished by the perpendicular plate of the palatine bone behind, the maxillary process of the inferior nasal concha below, and above this by the uncinate process of the ethmoid. The opening is further curtailed by the adjacent mucous membrane. Under these circumstances it is reduced to a small aperture, situated near the upper part, which opens into the middle meatus of the nasal fossa. The sinus is usually unilocular, but it may be partially divided into compartments.



Fig. 139. — The Foetal Maxilla.

A, lateral aspect, showing the infra-orbital groove and foramen, with fissure; B, inferior view, showing the incisive fissure and sockets; C, medial aspect, showing the maxillary sinus and incisive fissure.


The bone derives its blood-supply from many sources, such as posterior superior dental, infra-orbital, anterior superior dental, facial, supratrochlear, greater palatine, and spheno-palatine arteries.

Articulations. — The maxilla articulates with nine bones as follows; zygomatic, nasal, frontal, lacrimal, ethmoid, inferior nasal concha, palatine, vomer, and its fellow of the opposite side. In addition to these it may articulate with the pterygoid process and greater wing of the sphenoid.

Structure. — The bone contains the maxillary sinus. For the most part cancellated tissue is absent, except in the alveolar process around the sockets.


Ossification. — The maxilla is ossified in membrane. According to Mall and Fawcett it has two centres —maxilla proper and premaxilla—which appear about the sixth week, and join about the third month. The centre referred to as maxilla proper appears in the region of the future canine socket, and from it ossification proceeds backwards into the zygomatic process, upwards into the posterior half of the nasal process, inwards into the posterior three-quarters of the palatine process, and downwards into the alveolar border, excluding the incisor portion.

The premaxilla centre gives rise to the premaxilla, which lies on the medial side of the maxilla proper and bears the upper incisor teeth. It also gives rise to (i) the anterior fourth of the palatine plate, and (2), according to Fawcett, the anterior half of the nasal process It is to be noted that, whilst the anterior half of the nasal process is ossified from the premaxilla centre, the posterior half of that process (bearing the lacrimal groove) is ossified from the maxilla proper centre.

Besides the premaxilla centre there is an infravomerine centre, according to Rambaud and Renault. This centre lies beneath the anterior part of the vomer, and it gives rise to the infravomerine part of the bone, which forms the medial wall of the incisive canal. The line of union between the premaxilla and maxilla proper is indicated by the premaxillary suture on the palatine surface of young bones, which may, though somewhat rarely, persist in adult life. This suture extends outwards and forwards from a point directly behind the lower end of the incisive canal to the alveolar border between the lateral incisor and canine sockets.

The premaxilla of each side forms an independent bone in many animals. It may be developed in two parts from separate centres of ossification—an inner for the portion bearing the central incisor socket, and an outer for the portion containing the lateral incisor socket, and these two portions may remain separate. 1 he inner portion is known as the endognathion, and the outer portion as the mesognathion, whilst the remainder and greater part of the bone is referred to as the ectognathion.

The varieties of alveolar cleft palate are explained by a reference to these coiiditions of the bone. In medial cleft palate the two premaxillae (right and left) are separated by a medial cleft. Lateral cleft palate may occur in two forms the maxilla proper or ectognathion and the entire premaxilla may fail to unite, and the cleft is situated between them, and invades the alveolar border between the lateral incisor and canine sockets; or the premaxilla may exist in two parts, inner or endognathion, and outer or mesognathion, and the cleft may be between these two, in which case it invades the alveolar border between the central and lateral incisor sockets. These conditions may occur on one or both sides.


In the earlier stages of intra-uterine life there is no trace of the maxillary smus, and the alveolar border lies close to the infra-orbital border. In the course of the fourth month, however, the sinus makes its appearance as a shallow depression on the inner aspect of the bone, and, as this increases, it gradually separates the orbital, alveolar, and palatine portions. In the process of development the alveolar border first presents an elongated furrow, called the dental groove, on either side of which a plate grows downwards, forming the labial and lingual plates. . Ihe groove is thus converted into a trench with these ramparts on either side. Subsequently these plates are connected by a number o septa, which intersect the trench and break it up into sockets. At this stage tnese are only five m number for each bone, and the canine socket is the first . f Petitioned off. In early life the bone contains the temporary teeth, w icn are five m number on either side, but in the adult, as stated, it contains eight alveoli for the eight permanent teeth.

The Zygomatic Bones

The zygomatic bone is situated between the zygomatic process of the frontal and zygoma of the temporal on the one hand, and the zygomatic process of the maxilla on the other, where it separates the orbit from the temporal fossa. It is quadrilateral, and presents two surfaces, four processes, and four borders. The lateral surface is convex, and near its* centre there is the zygomatic tuberosity. Above this is the zygomatic foramen for the passage of the zygomatico-facial branch of the zygomatic nerve. The portion of this surface close to the zygomatic process gives origin to the zygomaticus major, and the lower and anterior part to the zygomaticus minor. The medial surface , which is concave, looks into the temporal fossa above and zygomatic fossa below, and it is overhung superiorly by a curved plate of bone, called the orbital process. Anteriorly it presents a rough, slightly serrated, triangular area for the zygomatic process of the maxilla. The orbital process projects backwards and inwards, in a curved manner, from the upper part of the medial surface on a level with the orbital border. It is triangular, and its superior or orbital surface presents a sweeping concavity, which enables it to form the front part of the outer wall of the orbit, and a portion of the floor. This surface is pierced by one or, it may be, two openings. If there is one, it ultimately leads to two canals— zygomatico-facial, which opens on the lateral surface; and zygomatico-temporal, which opens on the temporal division of the medial surface, as a rule near the frontal process. These canals transmit the zygomatico-facial and zygomatico-temporal branches of the zygomatic nerve. If there are two, each leads to its own canal.




Fig. 140. — The Right Zygomatic Bone (Lateral Surface).


The inferior surface of the orbital process, which is convex, forms the anterior part of the temporal fossa. The rough margin of the process articulates by its superior part with the anterior border or zygomatic crest of the greater wing of the sphenoid, and below with a part of the orbital plate of the maxilla. The part of this border between the sphenoidal and maxillary portions usually closes the anterior and outer extremity of the inferior orbital fissure, and thus intervenes between the greater wing of the sphenoid and the superior maxilla.

The processes are four in number—superior, posterior, inferior, and anterior. The superior or frontal process is stout and prominent. Its direction is vertically upwards, and it terminates in a thick serrated extremity for the zygomatic process of the frontal. The posterior or temporal process is short and usually blunt. Its direction is backwards, and it terminates in a serrated extremity which is mortised into the zygomatic process of the temporal. The inferior or maxillary process is blunt and truncated. Its direction is downwards, and it articulates with part of the zygomatic process of the maxilla. The anterior or infra-orbital process is slender and pointed. Its direction is forwards, and it articulates with the maxilla near the infra-orbital foramen.


Fig. 141. — The Right Zygomatic Bone (Medial Surface),



1 he borders are four in number—temporal, masseteric, maxillary, and orbital. The temporal border extends from the frontal process to the temporal process, and is directed backwards. It is sinuous, and C ??^ 1 ? U0US W ^ ,J the upper border of the zygomatic, and it gives attachment to the temporal fascia. Near the frontal process it usually presents a sught prominence, called the marginal tubercle , to which a s out slip of the temporal fascia is attached. The masseteric border extends from the temporal process to the maxillary process, and looks ownwards. It is thick, rough, and continuous with the lower border o e zygomatic arch, and it gives origin to the anterior fibres of the superficial part of the masseter. The maxillary border extends from the maxillary process to the infra-orbital process, and it looks forwards and slightly downwards. It is rough and slightly concave, and, together with the rough, slightly serrated, triangular area on the medial surface adjacent to it, articulates with the zygomatic process of the maxilla. The orbital border extends from the infra-orbital process to the frontal, and is smooth, round, and concave. Its direction is outwards and upwards, and it forms a large part of the circumference of the orbit.

The bone derives its blood-supply from the lacrimal, deep temporal, and transverse facial arteries.

Articulations. — The zygomatic bone articulates with four bones, as follows: superiorly with the frontal and sphenoid, posteriorly with the temporal, and anteriorly with the maxilla.

Structure. — The bone is mainly composed of compact tissue, the amount of cancellous tissue being small.

Varieties. — The bone may persist in two parts connected by a suture, which may be horizontal or vertical It sometimes persists in three parts.

Ossification. — The zygomatic is developed in membrane from three centres, which appear in the eighth week of intra-uterine life, and they unite at the end of the fourth month. These centres are called prezygomatic, postzygomatic, and hypozygomatic. If all three centres should fail to unite, then a tripartite zygomatic is the result. If the prezygomatic and postzygomatic unite, and the hypozygomatic remains separate, a bipartite zygomatic persists with a horizontal suture. If the postzygomatic and hypozygomatic unite, and the prezygomatic remains separate, the suture is vertical. A bipartite zygomatic occurs with great frequency amongst the Japanese, and from this circumstance the bone is known as the os Japonicum.


The Nasal Bones

The nasal hone, which articulates with its fellow by its medial border, forms with it the bridge of the nose. It lies in front of the frontal process of the maxilla, where it enters into the formation of the face and nasal fossa. The bone is elongated from above downwards, and presents two surfaces and four borders. The anterior or facial surface is smooth, concavo-convex from above downwards, and convex from side to side. Near its centre it usually presents a minute foramen for the passage of a small vein from the nose to the commencement of the facial vein. The posterior or nasal surface is rough superiorly, where it articulates with the nasal spine of the frontal. Elsewhere it is smooth and concave from side to side, and in the recent state is covered by the nasal mucous membrane. It is traversed longitudinally near the centre by the ethmoidal sulcus for the anterior ethmoidal nerve.

The superior border is short, thick, and serrated for the nasal spine of the frontal. The inferior border is thin and expanded for the lateral nasal cartilage. It usually presents the nasal notch, which is situated near its inner end. The medial border articulates with its fellow. It is usually rather shorter and thicker than the lateral, and projecting backwards from it is a ledge of bone which, with its fellow, forms the nasal crest for articulation with the nasal spine of the frontal and the

anterior border of the perpendicular plate of the ethmoid. The lateral border, long and thin, is finely serrated for the frontal process of the maxilla.

The bone receives its blood-supply from the angular branch of the facial, and the dorsal nasal and anterior ethmoidal branches of the ophthalmic arteries.

Articulations. — The nasal articulates with four bones, as follows: superiorly with the frontal, laterally with the maxilla, medially with its fellow, and posteriorly with the ethmoid and again with the frontal.

Structure. — The bone is composed of compact tissue, and is therefore dense.

Ossification. — The nasal is developed in membrane from one centre, which appears about the eighth week of intra-uterine life.



Fig. 142. — The Right Nasal Bone.

A, anterior view; B, pos terior view.


The Lacrimal Bones

The lacrimal hone is situated at the anterior part of the inner wall of the orbit, where it lies behind the frontal process of the maxilla, and in front of the orbital plate of the ethmoid. It is very thin and scale-like. From its resemblance in this sense to a finger-nail, it is known as the os unguis. It is quadrilateral and presents two surfaces and four borders, the inferior border being recognized by its presenting a hamular and a descending process. The lateral or orbital surface is traversed by the lacrimal crest, which is nearer the anterior than the posterior border, and divides the surface into two unequal parts. The anterior division, representing one-third, completes the lacrimal groove, which lodges the lacrimal sac and the commencement of the nasolacrimal duct. The lower end of this division is prolonged into the descending process, which takes part in the wall of the lacrimal canal, and articulates with the lacrimal process of the inferior nasal concha, the posterior division, representing two-thirds, is smooth and forms part of the inner wall of the orbit. The lacrimal crest gives origin to the lacrimal part of orbicularis oculi, and inferiorly terminates in a hook-like projection, called the lacrimal hamulus. This process is curved in a forward direction, and is received into the lacrimal notch at the front part of the medial border of the orbital plate of the maxilla, where it bounds laterally the superior orifice of the lacrimal canal, it articulates with the lacrimal tubercle of the maxilla. The medial surjace piesents a vertical furrow corresponding with the position of the lacrimal crest on the lateral surface. Superiorly it articulates with the front part of the labyrinth of the ethmoid, where it helps to close ethmoidal sinuses and forms part of the infundibulum. Inferiorly it forms part of the outer wall of the nasal fossa, and looks into the middle meatus.

The superior border is short, and articulates with the frontal. The inferior border, behind the lacrimal crest, articulates with the medial border of the orbital surface of the maxilla, whilst in front of the crest it forms, as stated, the descending process, and articulates with the lacrimal process of the inferior nasal concha. The anterior border articulates with the posterior border of the frontal process of the maxilla. The posterior border articulates with the anterior border of the orbital plate of the ethmoid.

Articulations. — The lacrimal articulates with four bones: superiorly with the frontal, anteriorly with the maxilla, inferiorly with the inferior nasal concha, and again with the maxilla, and posteriorly with the ethmoid.

Structure. — The bone consists of a thin translucent plate.

Varieties. — Very occasionally the bone may extend beyond the margin of the orbit on to the face.

Ossification. — The lacrimal is developed in membrane usually from one centre, which appears during the third month of intra-uterine life.


The Inferior Nasal Conchse

The inferior nasal concha is situated on the outer wall of the nasal fossa, where it overhangs the inferior meatus, and is in series with the middle nasal concha of the ethmoid. It is elongated from before backwards, and presents two surfaces, two borders, and two extremities. The lateral surface is concave, and is overhung above, over about its middle third, by the maxillary process. It looks towards the outer wall of the nasal fossa. The medial surface is irregularly convex, pitted, and marked by a few antero-posterior grooves. It bulges into the nasal fossa, and limits inferiorly the middle meatus.

The superior border, which is attached, slopes downwards and forwards in front, where it articulates with the conchal crest of the maxilla. Behind this it presents a slight concavity, limited in front by the lacrimal process, which articulates with the descending process of the lacrimal, and forms part of the lacrimal canal. Behind the concavity is the ethmoidal process for the uncinate process of the ethmoid. The portion of the superior border between these two processes is folded downwards and outwards into a thin plate, called the maxillary process, which forms part of the inner wall of the maxillary sinus below the opening of that cavity. Behind the ethmoidal process the superior border slopes downwards and backwards, and articulates with the conchal crest of the palatine bone. The inferior border is convex, thick, pitted, and free. The anterior extremity is short and stunted, whilst the posterior is long, slender, and pointed.



Fig. 143. — The Right Lacrimal Bone (External View).



Articulations. — The inferior nasal concha articulates with the following four bones: maxilla, lacrimal, ethmoid, and palatine.

Structure. — The bone is light and porous.

Ossification. — The inferior nasal concha is developed in cartilage from one centre, which appears in the fifth month of intra-uterine life.


Fig. 144. — The Right Inferior Nasal Concha. A, medial aspect; B, Lateral aspect.


The Palatine Bone

The palatine bone enters into the formation of the hard palate, he outer wall of the nasal fossa, and the floor of the orbit. It consists of a horizontal and perpendicular plate, which meet at a right angle, and of four processes: the tubercle, situated at the meeting of the wo plates posteriorly; and orbital and sphenoidal processes, situated at the upper extremity of the perpendicular plate, where they are separa ed by the spheno-palatine notch; and the maxillary process in


I he horizontal plate is quadrate, and presents two surfaces and four or ers. e superior or nasal surface is smooth and concave from side to side. It forms the posterior fourth of the floor of the nasal T °f a ' a p . 1S covere d m the recent state by the nasal mucous membrane, ihe »»/mor or palatal surface forms the posterior fourth of one-half t f df P a at \and near its posterior border it presents a short

p-rnnrx; cmd* ^ w ? llc ^ serves to divide the palatine glands into two groups, and gives insertion to a portion of the tendon of the tensor palati. The anterior border is serrated for the posterior border of the palatine process of the maxilla. The posterior border is concave and sharp. It gives attachment to one-half of the soft palate, and at its inner extremity it forms a backward projection, which, with its fellow, constitutes the posterior nasal spine, for the attachment of the musculus uvulas. The lateral border is attached, and meets the perpendicular plate at a right angle. On its outer aspect posteriorly it is excavated by the lower part of the greater palatine canal. The medial border is thick and serrated, and articulates with its fellow, forming an upward elevation, called the nasal crest. This crest is continuous with that of the palatine processes of the maxillae, and, like it, is grooved superiorly for a portion of the inferior border of the vomer.

The perpendicular plate rises upwards from the outer border of the horizontal plate. It is long and thin, and presents two surfaces and four borders. The medial surface forms part of the outer wall of the


F!g. 145. — The Right Palatine Bone (Medial Aspect).


nasal fossa, and is crossed from before backwards by two ridges. The lower ridge is called the conchal crest, and articulates with the posterior sloping part of the superior border of the inferior nasal concha. The upper ridge, which crosses the roots of the orbital and sphenoidal processes, is called the ethmoidal crest, and it articulates with the middle nasal concha of the ethmoid. Below the conchal crest is a smooth groove, which forms part of the inferior meatus of the nose; between the conchal and ethmoidal crests is another groove, which forms part of the middle meatus; and above the ethmoidal crest there is a third groove, which forms part of the superior meatus. The lateral surface is divided into three vertical strips, of which the anterior and posterior overlap and articulate with the maxilla and medial pterygoid plate respectively. The middle strip forms the inner wall of the pterygopalatine fossa, and is prolonged below into a groove which completes the greater palatine canal for the greater palatine nerve and its accompanying artery.


The anterior border of the perpendicular plate presents, just below the conchal crest, a leaf-like projection, called the maxillary process, which closes the lower and back part of the opening of the maxillary sinus. Superiorly it articulates with the ethmoid, and inferiorly with the maxilla. The posterior border articulates superiorly with the anterior border of the medial pterygoid plate of the sphenoid, and inferiorly it is prolonged into the tubercle. The inferior border is attached, and meets the horizontal plate. The superior border presents the orbital and sphenoidal processes and the spheno-palatine notch, to be presently described.

The tubercle of palatine bone projects backwards, downwards, and outwards from the meeting of the horizontal and perpendicular plates, and is received into the pterygoid fissure of the sphenoid. Posteriorly it presents three grooves. The central groove forms part of the pterygoid fossa, and gives origin to fibres of the medial pterygoid. The grooves on either side are rough, and articulate with the anterior borders of the corresponding pterygoid plates. The tubercle on its inferior aspect, close to the horizontal plate, presents two small openings, which are the orifices of the greater and lesser palatine foramina, the latter being the smaller of the two, and inconstant. These canals transmit the greater and lesser palatine nerves and arteries. Medially the tubercle gives origin to a few fibres of the superior constrictor muscle of the pharynx. Laterally there is a small free surface, which looks into the zygomatic fossa, between the pterygoid process of the sphenoid and the tubercle of the maxilla.


Fig. 146. — The Right Palatine Bone (Lateral Aspect).



The orbital process is the larger and more anterior of the two superior processes, and is often considered the most difficult piece of bone in the body to describe and to understand. First it must be realized as an inverted pyramid, attached to the top of the palatine bone by its apex, having four sides and a base. Then, in the inner wall of the orbit, it should be noticed that the orbital plate of the ethmoid, the sphenoid, and the maxilla, where they meet in the lower and back part of the orbit, each have a little piece bevelled off to enclose three sides of a diamond-shaped space, the fourth side being free in the pterygo-palatine fossa. It is into this diamond-shaped space that the orbital process of the palatine bone is wedged, so that one surface, looking forwards and inwards, rests against the orbital plate of the ethmoid and forms the ethmoidal surface.

Another, the sphenoidal, is directed backwards and inwards against the sphenoid; a third, forwards and outwards against the maxilla; a fourth, looking backwards and outwards, known as the sphenomaxillary (zygomatic) surface, has no bone to rest against, but lies free in the pterygo-palatine fossa; while the fifth or orbital surface, which is the base of the pyramid, makes a lozenge-shaped tile at the junction of the inner wall and floor of the back of the orbit.


Fig. 147. — The Right Palatine Bone (Posterior View).


Lastly, it must be realized that the process is a hollow pyramid, and that the air space which it contains communicates with the posterior ethmoidal sinus either on the ethmoidal or, where the sinus is completed, on the sphenoidal surface.

The sphenoidal process surmounts the posterior border of the perpendicular plate, and is an incurved flange. It has two surfaces and three borders. The superior or sphenoidal surface , which is grooved, articulates with the inferior surface of the body and the vaginal process of the sphenoid. The groove on this surface, with that on the under surface of the vaginal process of the medial pterygoid plate, forms the pterygo-palatine canal for the greater and lesser palatine vessels and nerves. The inferior or nasal surface is scooped out, and forms part of the outer wall and roof of the nasal fossa. The anterior border bounds the spheno-palatine notch posteriorly, and may be projected over it to join the orbital process. The posterior border articulates vith the medial pterygoid plate of the sphenoid. The internal border irticulates with the ala of the vomer.


The spheno-palatine notch is situated between the orbital and sphenoidal processes, and is converted into a foramen usually by the inferior surface of the body of the sphenoid, representing the part formed by a sphenoidal concha. It leads from the pterygo-palatine fossa behind the superior meatus of the nose, and transmits the medial branches of the spheno-palatine ganglion and spheno-palatine artery.

Articulations. — The palate bone articulates with six bones, as follows: the maxilla, inferior nasal concha, ethmoid, vomer, sphenoid, and its fellow.

Structure. — The bone is very thin, especially over the upper part of the perpendicular plate.

Varieties. — (i) The groove for the greater palatine canal may be bridged over. (2) The lesser palatine canal may be absent. (3) The spheno-palatine notch may be converted into a foramen by a forward extension of the sphenoidal process.

Ossification. — The palatine bone is ossified in membrane from one primary centre. The primary centre appears about the seventh week, at the angle of junction between the horizontal and perpendicular plates, or in the perpendicular plate (Fawcett). There may be a secondary centre for the orbital process.


The Vomer

The vomer is situated in the median plane, and forms part of the septum of the nose. It presents two surfaces, four borders, and an anterior extremity. The surfaces are disposed laterally, and each looks into the corresponding nasal fossa. Traversing each there is


Fig. 148. — The Vomer (Lateral View).


a groove, directed forwards and downwards, for the long sphenopalatine nerve.

The superior border is characterized by two thick, everted alse, separated by a groove, which receives the rostrum of the sphenoid. Each ala by its upper aspect fits against the inferior surface of the body of the sphenoid, and the lateral margin of each meets the vaginal process of that bone, and also articulates with the medial border of the sphenoidal process of the palatine bone. The inferior border is irregular, and is received into the groove which marks the nasal crests of the palatine processes of the maxillae and palatine bones. The anterior border is sloped downwards and forwards, and it may present two alae, but these are very thin, and lie near each other, being separated by a narrow cleft. These characters are always more pronounced in earlier life. The cleft in its lower part receives the septal nasal cartilage, and superiorly the perpendicular plate of the ethmoid fits into it, being usually ankylosed with one or both alae. In many cases, however, the anterior border is simply grooved. The posterior border is sharp and almost vertical, and lies between the posterior nares. The anterior extremity forms a short irregular lip, which touches the back parts of the incisive crests of the maxillae.

Articulations. — The vomer articulates with six bones, as follows: the sphenoid, two palatine bones, ethmoid, and maxillae. In addition to these, it articulates with the septal nasal cartilage.

Structure. — The-yomer is composed of two thin plates of compact bone, which are blended into one, except superiorly, and, it may be, to a certain extent anteriorly.

Varieties. — The bone is often much deflected to one or other side, more frequently the left, and so it may curtail the cavity of the nasal fossa to which it is deflected.

Ossiflcation. — The vomer is developed in membrane from two centres, which appear about the eighth week of intra-uterine life. The centres unite below in the third month, and form a groove in which the septal nasal cartilage lies. The laminae forming the lips of the groove continue to grow upwards and forwards and subsequently fuse, the enclosed cartilage becoming absorbed. Ultimately there are left the alae on the superior border, and, it may be, on the anterior border, which are permanent indications of the original bilaminar condition of the bone.


The Mandible

The mandible supports the lower teeth, and articulates at either side with the anterior part of the articular fossa of the temporal in a freely movable manner. It has the shape of a horse-shoe, and consists of a central horizontal portion, called the body, and two upright portions, called the rami.


The body is arched, being convex in front and concave behind, and it presents two surfaces and two borders. The lateral surface presents a slight median vertical ridge over its upper two-thirds, which marks the symphysis or place of union of the two halves of which the bone is originally composed. This ridge bifurcates at the lower third, and its two divisions, diverging, pass to the lower border, where each terminates in the mental tubercle. Between these diverging divisions there, is a triangular elevated surface, called the mental protuberance or chin, a feature only found in man. On either side of the symphysis is the incisive fossa, which gives origin to the mentalis and a deep slip pf the orbicularis oris. A little lateral to this fossa is the mental foramen, which opens outwards and backwards from the inferior dental

anal, and transmits the mental nerve and vessels. This foramen is Ln line with the septum between the two premolar sockets, and in the adult it is midway between the superior and inferior borders. Below it is the oblique line, which extends from the mental tubercle to the lower extremity of the anterior border of the ramus. This line gives origin to the depressor anguli oris. The lower part of the lateral surface, from near the symphysis to about the level of the mental foramen, gives origin to the depressor labii inferioris.

The medial surface presents a slight median groove over about its upper two-thirds, which coincides with the symphysis. Lower down there are four small projections, called collectively the genial tubercles, which are arranged in pairs on either side of the middle line. The upper spine gives origin, at either side, to the genio-glossus, and the lower to the genio-hyoid. Close to the lower border, at either side of the symphysis, is the oval digastric fossa, which gives origin to the anterior belly of the digastric. Coinciding with the position of the oblique line there is the mylo-hyoid line. This commences near the symphysis below the lower genial tubercle, and, passing obliquely backwards and upwards, it terminates a little behind the last molar socket. It gives origin to the mylo-hyoid muscle over its whole length, whilst at its upper and back part it gives attachment to some fibres of the superior constrictor muscle of the pharynx and the pterygomandibular ligament. Below the posterior part of this ridge is the submandibular fossa for the submandibular gland, and above its anterior part is the sublingual fossa for the sublingual gland.


Fig. 149. —The Left Half of the Mandible (Lateral Aspect).


The superior or alveolar border is excavated into sixteen sockets, eight in each half of the bone, which correspond with those in each maxilla. The outer surface of the alveolar arch, over the extent of the three molar sockets at either side, gives origin to some fibres of the buccinator. The inferior border or base terminates, at either side, on a level with the anterior border of the ramus. It projects more than the superior border, and gives insertion on its outer aspect to a portion of the platysma. Near its termination it is marked by a short vertical groove for the facial artery.

The ramus rises, at either side, from the extremity of the body. It is compressed from without inwards, and presents two surfaces and four borders. The lateral surface gives insertion to the masseter, and, m the vicinity of the angle, it presents a few oblique ridges for the tendinous bands of that muscle. The medial surface presents, a little below its centre, the mandibular foramen, which is on a level with the summit of the crown of the third molar tooth. This foramen leads to the mandibular canal, which traverses the bone to near the symphysis, and from which, near its anterior part, the mental foramen opens on the lateral surface. This canal lodges the inferior dental nerve and vessels, and communicates with the foramina which open on the extremities of the fangs of the teeth. The mandibular foramen presents anteriorly and medially a thin, sharp plate of bone, called the lingula.



Fig. 150. — The Left Half of the Mandible (Medial Aspect).



Behind the lower end of the latter is a short crescentic margin on the inner aspect of the foramen, and proceeding downwards and forwards from this is the mylo-hyoid groove, which terminates a little below the posterior extremity of the mylo-hyoid line, and transmits the mylo-hyoid nerve and artery. The spheno-mandibular ligament is

attached to the lingula and to the crescentic margin behind it. Between the mandibular foramen and the angle there is a rough impression, often strongly ridged, which gives insertion to the medial pterygoid.

The anterior border is continuous with the oblique line opposite the third molar socket, and is shorter than the posterior. The posterior border meets the inferior border, thus forming the angle, which, in muscular subjects, is strongly marked and slightly everted. Laterally and medially it presents rough impressions for portions of the masseter and medial pterygoid respectively, and between these muscles it gives attachment to the stylomandibular ligament. The angle is obtuse, and in the adult amounts on an average to 120 degrees. In early infancy it is as much as 150 degrees, and in old age it amounts to about 140 degrees. The inferior border is continuous with the inferior border or base of the body. The superior border presents the mandibular notch, the coronoid process, and the condyloid process.



Fig. 152. — Cartilage of Mandibular Arch (Meckel’s). (From Keibel and Mall, After Kollmann.)


ine mandibular notch communicates with the zygomatic fossa, and transmits the masseteric nerve and artery to the deep surface of the masseter.

The coronoid process surmounts the anterior border of the ramus, and is triangular and compressed from without inwards. Its lateral surface gives insertion to fibres of the masseter, and its medial surface, as well as the superior and anterior borders, to part of the temporal muscle. The medial surface is marked by a ridge which extends downwards on the medial surface of the ramus, not far from the anterior border, to a point on the inner side of the last molar socket, where it becomes continuous with the mylo-hyoid line. The temporal muscle continues to take insertion into this ridge, as well as into the elongated triangular depression between it and the anterior border of the ramus.


Fig. 151. — The Mandible at Birth.



The condyloid process surmounts the posterior border of the ramus. It is oval and convex, and it articulates with the anterior part of the articular fossa of the temporal, an interarticular fibro-cartilage intervening. Its long axis is oblique, so that the axes of the two condyles, if sufficiently prolonged inwards and slightly backwards, would meet near the anterior margin of the foramen magnum. Laterally the condyloid process presents a projection, called the condylar tubercle, for the temporo-mandibular of the mandibular joint. Below the condyloid process is the neck, which presents anteriorly a depression for the insertion of the greater part of the lateral pterygoid muscle. Articulations.—With the articular fossae of the temporal bones. Structure.—The mandible is composed of two dense plates of compact bone, which are particularly strong in the region of the base, but become thinner superiorly at the alveolar border. Between these plates there is cancellous tissue with wide meshes.


Ossification. — The mandible is a mixed bone, being chiefly a membrane bone, but in part also a cartilage bone . It is ossified in connection with Meckel’s cartilage and its fibrous investment. Each half of the bone has one centre (Low and Fawcett), which appears about the sixth week of intra-uterine life, being only preceded by the primary centres for the clavicle. It is deposited in the membrane which covers the outer surface of Meckel’s cartilage in the region of the future mental foramen. From this centre one-half of the bone is ossified, chiefly in membrane, but also in cartilage—namely, the medial end of Meckel’s cartilage, and certain other accessory cartilages. The original centre gives membranous origin to (i) the walls of the sockets and mandibular canal, (2) the basilar border and angle, and (3) the ramus as high as the mandibular foramen. The medial part of Meckel’s cartilage is invaded by osseous extension from the primordial membrane bone formed from the single centre, the medial part of Meckel’s cartilage becoming incorporated with the bone so formed and constituting the incisive portion of the mandible.

The accessory cartilages, which are distinct from Meckel’s cartilage, are as follows: (1) Condyloid, (2) coronoid, and (3) symphysial. All these accessory cartilages become surrounded and invaded by osseous extension from the primordial membrane bone formed from the single centre, and they become incorporated with the parts of the mandible so formed.

The condyloid cartilage gives rise to (1) the condyloid process, and (2) the posterior part of the ramus as low as the mandibular foramen. The coronoid cartilage gives rise to (1) the coronoid process, and (2) the anterior part of the ramus as low as the mandibular foramen. The symphysial cartilage gives rise to the limited symphysial part of the mandible.

At birth the mandible consists of two halves, connected at the symphysis by fibrous tissue. In the course of the first year osseous union takes place, which is completed towards the end of the first year or beginning of the second year.

Meckel’s cartilage, which represents a large part of the first visceral arch, extends on either side downwards and forwards from the periotic cartilaginous capsule to the median line, where it meets its fellow. It is surrounded by a fibrous investment. The proximal end of the cartilage gives rise to the malleus and incus, two of the three ossicles of the tympanic cavity. The part of the cartilage between the periotic cartilaginous capsule and the mandibular foramen disappears, and the membranous investment of this part persists as the sphenomandibular ligament. The part of the cartilage between the mandibular foramen and the mental foramen also disappears, and its membranous investment undergoes ossification from a single centre, and gives rise to (1) the greater part of one-hali of the body of the mandible (incisive and symphysial parts excepted), and (2) the lower half of the ramus as high as the mandibular foramen. The manthble^^ °* s car til a ge> wdien ossified, becomes the incisive part of the

At birth the inferior border is but little developed, and the body is consequen y s a ow. Ihe rami are very short, so that each condyloid process is near y on a evel with the upper border of the symphysis, and the coronoid process is rather longer than the condyloid process. The mental foramen is nearer the inferior than the superior border, and the angle amounts to 150 degrees or more. Subsequently the body increases in depth, the rami lengthen, the angle decreases, and the mental foramen gradually assumes a position midway between the superior and inferior borders. In old age, after the bone becomes edentulous, the alveolar border undergoes absorption, the body consequently becomes shallower, the mental foramen lies near the superior border, the rami droop backwards, and each angle becomes increased to about 140 degrees. For the development of the alveolar arch, and its relation to the milk-teeth, see the maxilla.


Greater Horn


The Hyoid Bone

The hyoid bone is situated in the median line of the neck, between the chin and the thyroid cartilage of the larynx, with which latter it is connected by means of the thyro-hyoid membrane and thyrohyoid ligaments. It is closely connected with the base of the tongue, and is hence known as the os lingucs. In its development it is associated with the skull, and it is suspended from the lower ends of the styloid processes of the temporal bones by two fibrous bands, called the stylohyoid ligaments (epi-hyals). It consists of a central portion or body and two pairs of horns (cornua), greater and lesser.

The body is elongated transversely, compressed from before backwards, and quadrilateral. Its surfaces, which are anterior and posterior, occupy an oblique plane, being sloped downwards and forwards. The anterior surface is convex, and is crossed transversely by a curved ridge, which divides it into an upper and a lower part, and is continuous with the roots of the lesser horns. At the middle line this is intersected at right angles by a vertical ridge, which, however, is often incomplete, being sometimes confined to the upper half, and sometimes to the lower. At the place of intersection of the two ridges there is a slight projection, called the hyoid tubercle. Each half of the anterior surface is thus mapped out into an upper and a lower irregular muscular division. The upper division, provided the upper border is not very thick, gives attachment to the genio-hyoid and genio-glossus, and the lower division to the digastric, stylo-hyoid, and mylo-hyoid. The posterior surface is concave, and is covered by the thyro-hyoid membrane as it ascends to be attached to the superior border, a synovial bursa intervening. This surface is related to the epiglottis. The superior border is somewhat thick, and occasionally is really a surface, in which cases it gives attachment to the genio-glossus, whilst its posterior lip gives attachment to the thyro-hyoid membrane. The inferior border is sharp, and gives insertion to the sterno-hyoid, superior belly of the omohyoid, and thyro-hyoid muscles. Each lateral border is connected with a greater horn.



Fig. 154. — The Hyoid Bone (Anterior View).


The greater horns project upwards, backwards, and outwards from the lateral borders of the body. Each is compressed from above downwards, and gradually diminishes in size to its termination, where it ends in a small tubercle for the attachment of the thyro-hyoid ligament. It gives attachment to fibres of the thyro-hyoid, hyo-glossus, middle constrictor muscle of the pharynx, and the thyro-hyoid membrane.

The lesser horns are short conical nodules, each of which projects upwards and backwards from the junction between the body and greater horn. Its tip gives attachment to the stylo-hyoid ligament, which is sometimes ossified, a possible condition to be borne in mind during digital examination of the upper part of the pharynx. Elsewhere it gives attachment to the middle constrictor muscle of the pharynx, and sometimes to the chondro- and cerato-glossus. The lesser horns may be wholly or partially cartilaginous, and they articulate with the body by a synovial joint, unless in advanced life, when ankylosis usually takes place.



Fig. 155. — The Hyoid Bone, showing its Muscular Attachments.


Ossification. — The hyoid bone is developed in connection with the second and third visceral arches. The cartilaginous bar of the second visceral arch is known as the hyoid bar, and is continuous with its fellow at the median line.

It is represented by the curved ridge, already described, joining the bases of the lesser horns. The cartilaginous bar of the third visceral arch is known as the thyro-hyoid bar, and at the median line it blends with the junction of the hyoid bars. With the foregoing proviso, the hyoid bone is developed from rive or, it may be, six centres. One or, it may be, two are deposited during the last month of intra-uterine life at the place of fusion of the two hyoid bars.

If there are two centres they soon join, and give rise to the greater part of the kpdy h*! the hyoid bone or basi-hyal. About the same time a centre appears at either side in the thyro-hyoid bar of the third visceral arch, and from these cenhes are developed the greater horns or thyro-hyals, and the adjacent portions of the body. Centres for the lesser horns (cerato-hyals) do not appear till shortly before puberty. About this time centres have been described for tips of greater horns, as epiphyses. The greater horns join the body in middle life, but the lesser horns do not join until advanced life. The stylo-hyoid ligaments may become ossified more or less completely, and so represent the epi-hyal bones of many animals.


The Skull as a Whole

Sutures

The only bone of the skull which has movable articulations is the mandible. Each condyloid process of that bone articulates with the anterior part of the articular fossa of the corresponding temporal bone, with the intervention of an interarticular fibro-cartilage, the articulation so formed being called the mandibular joint.

The other bones of the skull, for the most part, are in close contact with each other, a small amount of fibrous tissue being interposed, which is continuous with the periosteum. These articulations are called sutures. Certain cranial bones, however, are separated at first by a plate of hyaline cartilage, the articulation being called synchondrosis. This, however, is a temporary joint, inasmuch as synostosis takes place after a certain period of life. It applies to (1) the articulation between the basilar process of the occipital and the body of the sphenoid, and (2) the articulation between the jugular process of the occipital bone and the jugular notch on the inferior surface of the petrous portion of the temporal bone.

The lambdoid suture connects the superior lateral borders of the squamous portion of the occipital bone with the posterior borders of the two parietal bones. The two limbs of the suture, right and left, become continuous with each other at the superior angle of the squamous portion of the occipital bone, from which point each limb passes outwards and downwards. The margins of the bones are strongly serrated, and along the course of the suture supernumerary ossicles, called sutural bones (Wormian bones), are frequently present.

The occipito-mastoid suture, on either side, connects the inferior lateral border of the squamous portion of the occipital bone with the posterior border of the mastoid part of the temporal bone. It is one of the bifurcations of the lower end of the corresponding limb of the lambdoid suture, the other bifurcation being the parietomastoid suture. Its direction is downwards and forwards.

The sagittal suture (interparietal) connects the superior borders of the two parietal bones. It is serrated, and occupies the median line, its direction being from behind forwards. Posteriorly it meets the lambdoid suture, the place of meeting constituting the lambda, which indicates the situation of the posterior fontanelle of early life. From the lambda three sutures radiate—namely, the sagittal suture and the two limbs of the lambdoid suture. Anteriorly the sagittal suture meets the coronal suture, the place of meeting constituting the bregma, which indicates the situation of the anterior fontanelle of early life. The part of the sagittal suture in the region of the two parietal foramina is usually less serrated than elsewhere, and is the first part to show signs of obliteration. It constitutes the obelion, which indicates the situation of the sagittal fontanelle of early intra-uterine life.

The coronal suture connects the frontal bone with the two parietal bones. It crosses the superior surface of the skull in an arched manner, extending on either side as low as the superior border of the greater wing of the sphenoid. As it crosses the median line it is joined by the anterior end of the sagittal suture. The place of junction is, as stated, called the bregma, which indicates the position of the anterior fontanelle of early life. From the bregma three sutures radiate—the sagittal, and the two limbs, right and left, of the coronal suture. Each limb of the coronal suture is serrated, but more so over the central part than the upper and lower parts, and more so over the upper part near the median line than over the lower part, which two latter situations overlapping takes place. Superiorly the frontal bone slightly overlaps the parietal bone, and inferiorly the parietal bone distinctly overlaps the frontal bone, the opposed bevelled surfaces in the latter region being ridged. This latter portion of the coronal suture is spoken of as a limbous suture.

The metopic or frontal suture, which connects the two halves of the frontal bone during the first year of life, may persist throughout lile. Under these circumstances, it extends in the median line from the bregma to the centre of the nasal notch of the frontal bone.

.P erl ° r ty continuous with the sagittal suture, and inferiorly

with the mternasal suture. Even though the suture may not persist entirely, traces of it may be present inferiorly. As a rule, however, the suture is entirely obliterated by the end of the second year of life.

. , ^ arie ^ 0 " mas ^°id suture is serrated, and anteriorly is continuous with the posterior end of the squamosal suture. It is on a level with



the upper border of the zygomatic arch. Its posterior extremity is the asterion, which indicates the situation of the postero-lateral or mastoid fontanelle of early life. From this point three sutures radiate—the lambdoid, the parieto-mastoid, and the occipito-mastoid.

The squamosal suture is arched, the convexity being directed upwards, and after having descended posteriorly, it becomes continuous with the parieto-mastoid suture. Anteriorly it is continuous with the spheno-parietal suture. The squamosal suture presents a marked contrast to the foregoing serrated sutures, inasmuch as it is a squamous suture, the squamous part of the temporal overlapping the lower border of the parietal bone.

The spheno-parietal suture connects the posterior part of the superior border of the greater wing of the sphenoid with the anteroinferior angle of the parietal bone. Its direction is from behind forwards. Posteriorly it is continuous with the squamosal suture,



Fig. 157. — Sutures of Right Lateral Surface of Skull.

S.P., spheno-parietal; S.F., spheno-frontal; P.S., parieto-squamosal;

X, pterion; C., coronal; S.S., spheno-squamosal.

and anteriorly with the spheno-frontal suture. The spheno-parietal suture, like the parieto-squamosal, is a squamous suture. The region of the spheno-parietal suture coincides with the pterion. The sphenoparietal suture may be very short, or entirely absent, in which latter case the lower and posterior part of the frontal bone articulates directly with the squamous part of the temporal bone, thus excluding the antero-inferior part of the parietal bone from any articulation with the greater wing of the sphenoid. In such cases the pterion is situated at the posterior end of the spheno-frontal suture. In all cases the guide to it is the lower end of the posterior border of the zygomatic process of the frontal bone, the pterion being situated about i\ inches behind it, and about 2 inches above the zygomatic arch. The pterion indicates the situation of the antero-lateral or sphenoidal fontanelle of early life. In this region a sutural bone, called the epipteric bone, is sometimes met with.


The fronto-squamosal suture is quite rare, but is the normal arrangement in monkeys.

The spheno-frontal suture, which is squamous, connects the superior border of the greater wing of the sphenoid bone with the lower part of the lateral aspect of the frontal.

In studying the sutures of the vault of the skull it will be noticed that they are much simpler intracranially than on the surface, and that they close internally much earlier than they do externally, except in two places. It has been found that, in English people, the internal obliteration begins soon after thirty, and is fairly complete by forty years of age. The two exceptions on the surface are at the obelion, between the parietal foramina, and in the coronal suture below the point where the temporal crest crosses it. At these two places obliteration is as early as it is inside the skull.

There are two other spheno-frontal sutures. One connects the rough triangular surface on the antero-superior part of the greater wing of the sphenoid bone with the rough triangular surface on the frontal bone behind the zygomatic process. This is a harmonic suture. The other spheno-frontal suture (orbitospheno-frontal suture) will be described under the orbital sutures. It also appears, however, in the anterior fossa of the internal surface of the base of the skull.

lhe spheno-squamosal suture connects the lateral border of the greater wing of the sphenoid bone with the antero-inferior border of the squamous part of the temporal bone, its direction being downwards and backwards as far as the inner end of the squamo-tympanic fissure. Its upper part forms a squamous suture, but its lower part is serrated.

lhe zygomatico-temporal suture connects the extremity of the zygomatic process of the temporal bone with the temporal process of the zygomatic bone by an oblique or else by a right-angled junction.

lhe fronto-maxillary suture, which is serrated, connects the lateral part of the nasal notch of the frontal bone with the superior border of the frontal process of the maxilla. It lies almost transversely.

The fronto-nasal suture connects the medial part of the nasal notch of the frontal bone with the superior border of the nasal bone. It lies transversely, and is serrated. Across the median line it is continuous with its fellow of the opposite side, and laterally it is continuous with the fronto-maxillary suture. The point corresponding to the meeting of the two fronto-nasal sutures coincides with the nasion.

i he internasal suture is vertical, and it is a harmonic suture. The lower end of the suture coincides with the rhinion.

lhe nasomaxillary suture is almost vertical, and it is finely serrated.

The zygomatico-maxillary suture connects the rough triangular -ea at the anterior part of the medial surface of the zygomatic bone W1 mu • rcm £>h superior surface of the zygomatic process of the maxilla.

I he intermaxillary suture is only partially seen on the facial surface 01 the skull. I his part extends from the centre of the anterior nasal spine to the point of meeting of the alveolar arches of the maxillae.


The palatine part of the suture connects the medial borders of the palatine processes of the maxillae. Its direction is antero-posterior, and it is a harmonic suture.

The interpalatine suture connects the medial borders of the horizontal plates of the palatine bones. It is continuous with the intermaxillary suture, and is a harmonic suture.

The transverse palato-maxillary suture connects the anterior border of the horizontal plate of the palatine bone with the posterior border of the palatine process of the maxilla.

The vertical palato-maxillary suture connects the lower part of the anterior border of the perpendicular plate of the palatine bone with the medial surface of the maxilla behind the opening of the maxillary sinus. It is a harmonic suture.

The premaxillary suture is described on p. 216.

The petro-squamosal suture connects the petrous and squamous parts of the temporal bone, and is situated on the inner or cerebral surface of the bone. Its direction is antero-posterior, and it extends from the petro-squamosal angle anteriorly to the parietal notch (entomion) on the superior border of the mastoid part posteriorly, where it meets the squamo-mastoid suture. It is a harmonic suture, and ankylosis usually takes place in the course of the first year of life. The suture, however, may persist until puberty, or later. Even though ankylosis takes place at the normal period of time, it may occur in such an imperfect manner that the suture is drilled by several channels. Under the foregoing circumstances pyogenic infection may extend from the tympanic cavity to the cerebral meninges and brain. The petro-squamosal venous sinus of foetal life extends along the petrosquamosal suture.

The squamo-mastoid suture connects the mastoid and squamous parts of the temporal bone, and is situated on the outer surface of the x>ne. Its direction is almost vertical, and it extends from the parietal lotch (entomion) on the superior border of the mastoid part anteriorly

o a point behind the posterior limb of the tympanic ring. The lower 3 art of the suture intervenes between the contiguous part of the nastoid part and the post-meatal plate of the squamous part, which atter forms the suprameatal triangle and outer wall of the antrum. Superiorly it meets the petro-squamosal suture. The squamo-mastoid

uture is a harmonic suture, and ankylosis usually takes place in the course of the first year of life. The suture, however, may persist intil puberty, or even throughout life. Even though ankylosis takes dace at the normal period of life, it may occur in such an imperfect nanner that the suture is drilled by several channels. Under these

ircumstances, pus may find an exit from the tympanic cavity to the ixterior.

The petro-sphenoidal suture connects a portion of the anterior )order of the petrous part of the temporal bone with the outer portion >f the posterior border of the greater wing of the sphenoid. It lies >bliquely, its direction being inwards and forwards.


The petro-basilar suture connects the inner half of the posterior border of the petrous portion of the temporal bone with the lateral border of the basilar portion of the occipital bone. Its direction is forwards and slightly inwards, and it is a harmonic suture. Superiorly it is grooved for the inferior petrosal venous sinus.

Schindylesis.—There are only a few examples of this variety of synarthrosis, or immovable joint, in the skull. These are as follows: (1) The articulation between the inferior border of the vomer and the cleft which lies along the nasal crests of the palatine processes of the maxillae and palatine bones; (2) the articulation between the rostrum of the sphenoid and the cleft on the superior border of the vomer between the two thick, everted alae; and (3) the articulation between the inferior border of the perpendicular plate of the ethmoid with the narrow cleft on the anterior border of the vomer.

Gomphosis.—This variety of synarthrosis is illustrated in the impaction of the roots of the teeth within the sockets of the maxillae and mandible.

Synchondroses

The following are examples of this temporary form of synarthrosis:

Spheno-occipital Synchondrosis.—This is situated between the posterior surface of the body of the sphenoid and the anterior surface of the basilar part of the occipital bone.

Petro-occipital Synchondrosis.—This is situated between the jugular notch on the inferior surface of the petrous part of the temporal bone and the extremity of the jugular process of the occipital.

Spheno-petrosal Synchondrosis.—This is situated between the posterior border of the greater wing of the sphenoid and the anterior part of the petrous portion of the temporal bone.

There are also intra-occipital and intra-sphenoidal synchondroses until the ossification of these bones is completed.

Regions

Before comparing the different aspects of two or more skulls it is obvious that they must be placed in the same position, or, to be more definite, orientated in the same plane. Craniologists have now agreed to accept what is known as the ‘ Frankfurt plane of orientation/ which is obtained by drawing a horizontal line from the lower margin of the orbit through the upper margin of the external auditory meatus.

1. The Posterior Aspect of the Skull.

The posterior aspect (norma occipitalis) is formed by the posterior parts of the parietal bones, the upper or interparietal division of the squamous part of the occipital, and the mastoid part of the temporal bones. A little above the centre it presents the lambda, which is the place where the sagittal meets the lambdoid suture in the situation of the posterior fontanelle of early life. Radiating from the lambda there are three sutures. One passes upwards and forms the posterior part of the sagittal suture. The other two, diverging, pass outwards and downwards, and form together the lambdoid or occipito-parietal suture. About 1 inch above the lambda, at either side of the sagittal suture, is the parietal foramen, and the point where the horizontal line connecting the parietal foramina intersects the sagittal suture is known as the obelion, the interval between coinciding with the situation of the sagittal fontanelle of early foetal life, and sometimes being regarded as the remnant of the median orbit for the pineal eye. This part of the sagittal suture is less serrated than elsewhere, and is the first to show signs of obliteration. At the lower part of the posterior region in the middle line is the external occipital protuberance, which is known as the inion. A little above this is the occipital point, which is the part in the median plane at the greatest distance from the glabella of the frontal. The squamous part of the occipital may present an occipital suture if the interparietal division persists as a separate bone.

2. The Skull viewed from Above.

The skull viewed from above (norma verticalis) varies in shape. It may be oval with its long axis antero-posterior, and broader behind than in front. Such skulls are called dolicocephalic, and in them the zygomatic arches are usually visible at either side from above, a condition known as phenozygous. In other cases the superior region assumes a more circular shape, due to the broadening of its anterior part. Such skulls are called brachycephalic, and in them the zygomatic arches are usually concealed from above, a condition known as cryptozygous. Some skulls are intermediate between the dolicocephalic and brachycephalic, and are known as mesaticephalic. The^ bones which enter into the superior region are the upper part of the frontal, the anterior parts of the parietals, and a very little of the occipital. Its limits will vary with the shape of the skull, which must, of course, be orientated on the Frankfurt plane. Sometimes the supraciliary arches are seen, sometimes they are hidden by the frontal eminences. The highest point is situated in the course of the sagittal suture, and is called the vertex. The sutures in this region are three in number—coronal, sagittal, and lambdoid; but there is sometimes a fourth—namely, the metopic. The skull, viewed from above, reveals certain parts of the posterior region—namely, the posterior portions of the parietals, with the parietal foramina and obelion, the lambda, the interparietal portion of the occipital, and the lambdoid suture.

3. The Anterior Aspect of Skull.

The anterior aspect (norma frontalis) is formed by a portion of the frontal, the nasals, maxillae, zygomatics, and the mandible. It is subdivided into two regions, frontal and facial.

The frontal region presents the frontal eminences, superciliary arches, zygomatic and medial angular processes, supra-orbital notches, or it may be foramina, all on either side of the median line, and the nasal eminence or glabella at the median line, between the two superciliary arches. The meeting of the two fronto-nasal sutures is known as the nasion. The centre of a line drawn from one temporal line to the other across the narrowest part of the frontal region is the ophryon.

The upper part of the facial region presents the openings of the orbits. These apertures are quadrilateral, with the angles rounded off, and the long axes directed outwards and a little downwards. Their vertical height varies a good deal, and is sometimes an important racial characteristic. They are separated at the median line by the bridge of the nose, which is formed by the nasal bones and the frontal processes of the maxillae, whilst laterally each orbit is limited by the zygomatic bone and the zygomatic process of the frontal. The point at the inner angle of the orbit where the horizontal fronto-maxillary suture meets the vertical lacrimo-maxillary suture is known as the dachryon, and the lower part of the internasal suture is known as the rhinion. Below the nasal bones is the anterior bony aperture of nose. It is bounded on either side by the nasal notch on the medial border of the maxilla, and above by the inferior borders of the nasal bones,, whilst interiorly in the median line is the anterior nasal spine in two halves. The central point of the base of this spine is known as the subnasal point. The anterior nasal aperture is the common external opening of the two nasal fossae, which are separated by a septum composed of bones and cartilage. Just below the aperture, on each side of the subnasal spine, a small depression, called the subnasal fossa, is sometimes seen. An inspection of each nasal fossa will reveal two bulging prominences on its outer wall, the lower of which is formed by the inferior nasal concha, and the upper by the middle nasal concha. Below the former is the inferior meatus, whilst between the two is the middle meatus. The outer wall, from its irregularity, thus presents a marked contrast to the floor, which is smooth and unbroken. The osseous septum is, as a rule, deflected to one side, most commonly the left, thus diminishing the capacity of the left fossa. Below the anterior nasal aperture are the alveolar arches of the maxillae, which lodge the upper teeth. The point where the anterior margins of these two borders meet in the median line is known as the alveolar point. Below these borders is the entrance to the buccal cavity, and below this is the alveolar arch of the mandible which lodges the lower teeth. The middle point of the anterior lip of the lower border of the mandible is known as the mental point or gnathion.

The maxillae having a wider range than the mandible, the upper teeth slightly overlap the lower. According to the degree of projection of the maxillary bones, skulls are spoken of as orthognathous, prognathous, or mesognathous.

The chief small foramina of the anterior region are as follows, from above downwards at either side: supra-orbital, at the junction of the outer two-thirds and inner third of the supra-orbital margin of the frontal (which in most cases is a notch); infra-orbital, in the maxilla near the infra-orbital margin; mental, in the mandible in line with the septum between the premolar sockets; and zygomatico-facial, situated above the zygomatic tuberosity. The supra-orbital, infraorbital^ and mental foramina are in the same perpendicular line, and transmit the following important sensory nerves, in order from above downwards: supra-orbital, infra-orbital, and mental, which are branches of the ophthalmic, maxillary, and mandibular divisions of the trigeminal ganglion on the sensory root of the fifth cranial nerve. The zygomaticofacial foramen transmits the zygomatico-facial branch of the zygomatic nerve from the maxillary division of the fifth.

The sutures in the anterior region are: zygomatico-frontal, frontomaxillary, lacrimo-maxillary, fronto-nasal, internasal, naso-maxillary, zygomatico-maxillary, and intermaxillary.

The Orbits. —The orbits have the shape of four-sided pyramids, their bases being directed forwards and outwards, and their apices backwards and inwards. The inner walls are nearly parallel, and occupy an antero-posterior plane, but the outer walls diverge, the plane of each being directed forwards and outwards, so that they almost form a right angle with each other. Each orbit is lined with periosteum, which is continuous with the dura mater through the superior orbital fissure, and it contains the eyeball, with the ocular muscles, nerves, and bloodvessels, the lacrimal gland, and a large amount of fat. It presents an apex, a base, and four sides or walls. The apex, which is directed backwards and inwards, is formed by the bar of bone separating the optic foramen from the superior orbital fissure, and just above and internal to this is the optic foramen. The base is free, and is directed forwards and outwards. Its circumference presents the zygomaticofrontal suture laterally, the zygomatico-maxillary inferiorly, and the fronto-maxillary medially. The walls are superior, inferior, lateral, and medial.

The superior wall or roof, which is thin and brittle, is formed mainly by the orbital plate of the frontal, and behind this by the lesser wing of the sphenoid. It is smooth and concave. Within the zygomatic process it presents the fossa for lacrimal gland, and near the medial angular process the trochlear fossa, which gives attachment to the fibrous pulley of the superior oblique muscle of the eyeball.

The inferior wall or floor is formed by three bones—namely, the orbital surface of the maxilla, lateral to which is a part of the orbital surface of the zygomatic, whilst posteriorly is the orbital process of the palatine bone. The floor is thin, and separates the orbit from the subjacent maxillary sinus. It is traversed from behind forwards by the infra-orbital canal, which posteriorly is a groove. At its anterior and inner part is the upper orifice of the lacrimal canal, and lateral to this is a small depression which gives origin to the inferior oblique muscle of the eyeball.

The outer wall looks forwards and inwards, and is formed mainly by the orbital surface of the greater wing of the sphenoid, and in



Fig. 158. — The Anterior Aspect of the Skull (Norma Frontalis et Facialis).

I, nasal; II, nas. proc. of maxilla; III, lacrimal; IV, ethmoid (orbital plate); V, orbital surface of zygomatic; VI, orb. surf, of greater wing of sphenoid; VII, orb. plate of frontal; VIII, orb. surf, of maxilla; IX, frontal; IX', temp. div. of frontal; X, parietal; XI, greater wing of sphenoid; XII, squam. port, of temporal; XIII, zygomatic; XIV, mandible; XV, temporal fossa.



front of this by a part of the orbital surface of the zygomatic. Between the outer wall and the floor is the inferior orbital fissure, the front part of which communicates with the infratemporal fossa, and the back part with the pterygo-palatine fossa. Between the outer wall and the roof, towards the posterior part, is the outer portion of the superior orbital fissure. The part of the orbital process of the zygomatic which forms the front part of this wall presents two foramina (sometimes one) leading to the zygomatico-facial and zygomatico-temporal foramina.

The inner wall is almost vertical, and looks directly outwards. It is formed by four (sometimes five) bones, in the following order from before backwards: (1) the frontal process of the maxilla; (2) the lacrimal; (3) the orbital plate of the ethmoid; and (4) the anterior part of the lateral surface of the body of the sphenoid. If there are five bones, the fifth is a portion of the sphenoidal concha, which would lie behind the orbital plate of the ethmoid. Between the inner wall and roof, in the fronto-ethmoidal suture, are the openings of the anterior and posterior ethmoidal or internal orbital foramina. At the anterior part of this wall is the lacrimal groove, which lodges the lacrimal sac, and behind this is the lacrimal crest, which gives origin to the lacrimal part of orbicularis oculi.

The orbital sutures are as follows: superiorly, the spheno-frontal; inferiorly, the zygomatico-maxillary and palato-maxillary; laterally, the spheno-zygomatic; and medially, from before backwards, the lacrimo-maxillary, lacrimo-ethmoidal, and spheno-ethmoidal, all of which three are disposed vertically, and fronto-ethmoidal, which is antero-posterior.

The orbit has ten (sometimes nine) openings communicating with it. (1) The superior orbital fissure, the wide inner end of which forms the apex of the cavity, whilst the narrow outer part lies between the roof and the outer wall. This fissure transmits (a) the third nerve, the sympathetic filament to the ciliary ganglion, the fourth, the three branches (frontal, lacrimal, and naso-ciliary) of the ophthalmic division of the fifth and the sixth cranial nerves; (b) the superior ophthalmic vein; (c) the orbital branch of the middle meningeal artery; and (d) a portion of the dura mater. (2) The optic foramen, situated above and medial to the apex, for the optic nerve and the ophthalmic artery, along with a plexus of sympathetic nerve fibres. (3) The supraorbital notch (or it may be foramen), on the supra-orbital margin, for the supra-orbital nerve and vessels. (4) The opening of the infraorbital canal, on the floor, transmitting the infra-orbital nerve and vessels. (5) The opening of the zygomatico-temporal foramen, and (6) the opening of the zygomatico-facial foramen, both on the outer wall, for the branches of the zygomatic nerve from the maxillary division of the fifth cranial nerve. (The temporal and zygomatic openings may be combined into one.) (7) The inferior orbital fissure, at the junction of the outer wall and floor, which transmits the maxillary nerve to become the infra-orbital, and the infra-orbital artery and inferior ophthalmic vein. (8) The naso-lacrimal canal, at the anterior part of the inner wall, for the naso-lacrimal duct. (9) The anterior ethmoidal foramen, and (10) the posterior ethmoidal foramen, both

situated on the inner wall, the former transmitting the anterior ethmoidal vessels and nerve, and the latter the posterior ethmoidal vessels and nerve.

Eight muscles take their origin within each orbit. The four recti arise from a fibrous ring surrounding the optic foramen. The levator palpebrae superioris arises above and in front of the optic foramen, and the superior oblique arises medial to the last named. The inferior oblique arises from the depression at the anterior and inner part of the floor, lateral to the orifice of the naso-lacrimal canal, and the lacrimal part of orbicularis oculi arises from the lacrimal crest behind the lacrimal groove.

The Nasal Fossae. — The nasal fossae are two in number, right and left, and they lie on either side of the median plane. They extend horizontally from before backwards, opening on the face by means of the anterior bony aperture of nose, and communicating posteriorly with the naso-pharynx by the posterior bony aperture of nose. The vertical and antero-posterior dimensions of each fossa greatly exceed the transverse. The two fossae are separated from each other by a partition, called the nasal septum, which is partly osseous and (in the recent state) partly cartilaginous. Each fossa presents a roof, floor, and two walls, inner and outer.

The roof over its central part is horizontal, but in front and behind it is inclined downwards. Six bones enter into its formation. The central portion is formed by one-half of the cribriform plate of the ethmoid. The sloping anterior part is formed by the grooved nasal margin of the frontal bone, by the side of the nasal spine, and the posterior surface of the nasal bone. The sloping posterior part is formed by portions of the anterior and inferior surfaces of the body of the sphenoid, the ala of the vomer, and a part of the sphenoidal process of the palatine bone. The central part of the roof is perforated by the foramina of one-half of the cribriform plate, including the nasal slit, and, at its back part, the aperture of the sphenoidal sinus opens into the spheno-ethmoidal recess.

The floor is smooth and concave from side to side. Over its anterior three-fourths it is formed by the palatine process of the maxilla, and over its posterior fourth by the horizontal plate of the palatine bone. Near its anterior extremity, close to the incisive crest of the maxilla, is the upper opening of the incisive canal.

The inner wall is known as the nasal septum. The osseous septum is formed by ten bones, in the following order, as nearly as possible from below upwards; the nasal crests of the palatine processes of the maxillae and palatine bones; the vomer; the perpendicular plate of the ethmoid; the rostrum of the sphenoid; the nasal crest of the nasal bones; and the nasal spine of the frontal. The anterior border of the osseous septum presents a triangular deficiency, which is occupied in the recent state by the septal cartilage. The posterior border is formed by the posterior border of the vomer, which lies between the posterior bony apertures of the nose. As previously stated, the septum is usually deflected to one side, most commonly the left.

The outer wall is characterized by great irregularity, and is formed by seven bones, in the following order, as nearly as possible from before backwards: (1) the nasal; (2) the frontal process of the maxilla;


Fig. 159.— Sagittal Section of the Anterior Part of the Skull to the Right of the Nasal Septum.

(3) the lacrimal; (4) the medial surface of the labyrinth of the ethmoid, presenting the superior and middle nasal conchae; (5) the inferior nasal concha, which lies below the last named; (6) the perpendicular plate of the palatine bone, together with parts of its orbital and sphenoidal processes; and (7) the medial pterygoid plate of the pterygoid process of the sphenoid.

The bulging projections on this wall are produced by the superior, middle, and inferior nasal conchas, in this order from above downwards.


and the deep channels thereby formed are known as the meatus. These are three in number—superior, middle, and inferior. The superior meatus is situated towards the back part of the outer wall, where it lies between the superior and middle nasal conchse. It is comparatively short, and is directed obliquely forwards and upwards. The posterior ethmoidal sinus opens into it anteriorly, and the spheno-palatine foramen opens just below and behind the superior nasal concha. The middle meatus, which is longer than the superior, lies between the middle and inferior nasal conchae. At its anterior part it turns upwards, and is continued into the passage known as the infundibulum, which communicates with the frontal sinus of its own side. The ascending part also communicates with the anterior ethmoidal sinus. The middle portion communicates with the middle ethmoidal sinus, and presents the opening of the maxillary sinus. The inferior meatus, the longest of the three, lies between the inferior nasal concha and the floor of the nasal fossa. Near its anterior part is the lower orifice of the lacrimal canal, which lodges the naso-lacrimal duct.

The Paranasal Sinuses. —These are hollow cavities lined with mucous membrane, which are contained within the following bones: the frontal, sphenoid, ethmoid, maxillae, and mastoid portions of the temporals. They communicate directly with the nasal fossae, except the mastoid air cells, which at either side are in communication, through the tympanic antrum, with the tympanic cavity, that in turn being connected by means of the pharyngo-tympanic tube with the nasal part of pharynx, at a point lateral to the posterior bony aperture of nose. The maxillary sinus appears about the fourth month of intra-uterine life, but the other sinuses do not appear until childhood, and they do not show much development until the period of puberty (see the individual bones). In old age they all tend to become enlarged.

The frontal sinus (by means of the infundibulum) and the anterior ethmoidal sinus open into the ascending front part of the middle meatus. Ihe middle ethmoidal sinus and the maxillary sinus open into the central portion of the middle meatus. The posterior ethmoidal sinus opens into the superior meatus, and the sphenoidal sinus opens into the spheno-ethmoidal recess.

The foramina which perforate the cribriform plate of the ethmoid transmit the filaments of the olfactory bulb, and are arranged in three sets, as follows:, a middle set, which are simple perforations, and a lateral and medial set, which lead into small canals. These canals descend on the inner surface of the labyrinth and corresponding part of the perpendicular plate respectively, branching and opening out as they descend. The nasal slit transmits the anterior ethmoidal artery and nerve.* The spheno-palatine foramen leads from the pterygopalatine fossa, and transmits the spheno-palatine nerves from the spheno-palatine ganglion and the spheno-palatine artery.

The nasal fossae open on the face through means of the anterior

There is often a separate foramen for the anterior ethmoidal nerve in front of, and lateral to, the nasal slit.


Dony aperture of nose. Each bony aperture is semipyriform, and is Dounded above by the lower border of the nasal, laterally by the nasal notch of the maxilla, and inferiorly by the premaxillary portion of that bone.

The posterior bony apertures of nose are situated at the posterior extremities of the nasal fossae, between the pterygoid processes of the sphenoid, and they communicate in the recent state with the nasal nart of the pharynx. They are oblong from above downwards, and their plane is oblique, being directed downwards and slightly forwards. Each bony aperture is bounded laterally by the medial pterygoid plate }f the sphenoid, medially by the posterior border of the vomer, which separates the two apertures, inferiorly by the posterior border of the tiorizontal plate of the palatine bone, and superiorly by the vaginal Drocess of the sphenoid, ala of the vomer, and sphenoidal process of the palatine bone.


4. The Lateral Aspect of Skull.

The lateral aspect of skull (norma lateralis) is formed by portions of nost of the skull bones. This region presents the zygomatic arch, md, from behind forwards, are seen the mastoid process, opening of

he external auditory meatus and suprameatal triangle, condyloid 3 rocess of the mandible, lying in the anterior part of the articular fossa, irticular eminence, and the mandibular notch and coronoid process )f the mandible, the latter lying within the front part of the zygomatic irch. The central point of the orifice of the external auditory meatus s known as the auricular point, and the outer side of the angle of the nandible is known as the gonion. The point, situated at the angle vhich the posterior border of the frontal process of the zygomatic nakes with the superior border of its temporal process, is known as the jugal point.

The sutures in this region are the zygomatico-frontal, sphenozygomatic, spheno-frontal, spheno-parietal, spheno-squamosal, coronal, squamosal, zygomatico-temporal, parieto-mastoid, and a portion of she occipito-mastoid.

The point where the superior temporal line crosses the coronal suture is known as the stephanion, and the point where the parietonastoid, occipito-mastoid, and lambdoid sutures meet is the asterion. rhe latter coincides with the position of the postero-lateral fontanelle n early life. The point near the anterior part of the parieto-mastoid suture, where a process of the parietal is received into the parietal lotch of the mastoid, is known as the entomion.

The lateral region is divided by the zygomatic arch into the tem>oral and infratemporal fossae, the former being above the arch, and he latter within and below it.

The temporal fossa is bounded above by the superior temporal ines of the frontal and parietal, and below by the upper border of the ygomatic arch laterally, and the infratemporal crest of the greater wing of the sphenoid medially. It is formed by five bones: in front by the orbital process of the zygomatic, above by the lower portions of the frontal and parietal, and below by the temporal division of the


Fig. 160. — The Lateral Aspect of the Skull (Norma Lateralis).

V" ; n ' n ’ parietal; III, occipital; IV, greater wing of sphenoid: zwoS?r h 01 VTrr° f tempo I al; V1 > mastoid portion of temporal; VII

XI lacrimal ^XTT^+h zy ^° 1 f a ^ 1 F, ; nasal; X, maxilla (frontal process) ? nma1, XI1 ’ eth moid (orbital plate); XIII, mandible.

e b nrnAH a i SUP ^ r i 0r ^ te ? n P 0ral line; 3 > inferior temporal line; 4, obelion; 10 soman - 6, + T ?^ 7 ’ astenon; 8 ' entomion; 9, auricular point;

14'S oointV tT 6 ? ltal . f0 ™' men; I2 ' alveolar point; 13, subnasal point; iq’ ODhrvon- In La . crlmal & r p ov e; 16, daclnyon; 17, nasion; 18, glabella;

Dortk)n UI nf C +v.°^ gl ' ea , ter V n & sphenoid and the squamous

greater win? of I em P° raL The place where the parietal, frontal, are related L 16 s P he / 101 d. and squamous portion of the temporal - related to one another, and more particularly the region of the spheno-parietal suture, is known as the pterion, which coincides with the position of the antero-lateral fontanelle of early life. In this situation a sutural bone is sometimes present, called the epipteric bone. The temporal fossa gives origin to the temporal muscle as high as the inferior temporal line, and the temporal fascia, which covers that muscle, is attached to the superior temporal line.

The inferior temporal fossa is situated below the level of the infratemporal crest of the sphenoid. It is bounded laterally by the ramus Df the mandible and the inner surface of the zygomatic arch, and, between the two, it communicates with the exterior by means of the mandibular notch. Medially it is bounded by the lateral pterygoid plate of the sphenoid. Superiorly it is limited by the infratemporal surface of the greater wing of the sphenoid below the infratemporal

rest, where it presents the foramen ovale and foramen spinosum, and by a small part of the squamous portion of the temporal. Anteriorly its wall is formed by the lower portion of the medial surface af the zygomatic bone and the infratemporal surface of the maxilla, which latter presents the openings of the dental canals. Its superior limit is the infratemporal crest of the sphenoid, the inferior limit being the molar portion of the alveolar arch of the maxilla and the lower border of the lateral pterygoid plate.

The contents of the fossa are as follows: the coronoid process of the mandible with the insertion of the temporal muscle; the lateral and medial pterygoid muscles; the first and second parts of the maxillary artery, and the pterygoid plexus of veins; the maxillary division of the ifth cranial nerve and its branches, together with the otic ganglion; the chorda tympani nerve; and the spheno-mandibular ligament.

The foramina which communicate with the fossa are: the foramen ovale; the foramen spinosum; the openings of the dental canals; and the inferior dental foramen.

The fossa presents two fissures—infra-orbital and pterygomaxillary.

The infra-orbital fissure lies horizontally between the greater wing of the sphenoid and the maxilla. Laterally it is closed, as a rule, by the zygomatic, but sometimes by the greater wing of the sphenoid, which may here articulate with the maxilla. Medially it is bounded by the infratemporal surface of the orbital process of the palatine bone. The fissure leads into the orbit, and transmits the maxillary nerve to become the infra-orbital, the infra-orbital vessels, the zygomatic branch of the maxillary nerve, the orbital branches of the sphenopalatine ganglion, the inferior ophthalmic vein, and numerous lymphatic vessels draining the orbit.

The pterygo-maxillary fissure lies vertically between the anterior border of the pterygoid process of the sphenoid and the posterior border nf the maxilla, at their upper ends. Interiorly the fissure is closed by the approximation of the bones forming its lips, a part of the tubercle of the palatine bone usually intervening between them, though direct articulation sometimes takes place between the pterygoid process and the maxilla. Medially the fissure is bounded by the perpendicular plate of the palatine bone. It transmits the maxillary artery to the pterygo-palatine fossa. The pterygo-maxillary fissure meets the infra-orbital fissure at a right angle, and situated deeply within this angle is the pterygo-palatine fossa.

The boundaries of the pterygo-palatine fossa are as follows: anteriorly, the infratemporal surface of the maxilla at its inner and back part superiorly; posteriorly, the base of the pterygoid process of the sphenoid, and the lower and inner part of the anterior surface of its greater wing; medially, the perpendicular plate of the palatine bone, with its orbital and sphenoidal processes; and superiorly, the under surface of the body of the sphenoid. The contents of the fossa are the third part of the maxillary artery, the maxillary nerve, and the sphenopalatine ganglion, along with their branches. Two fissures communicate with this fossa: the infra-orbital, leading into the orbit, and the pterygo-maxillary, opening into the infratemporal fossa. It also communicates with the superior meatus of the nose by means of the spheno-palatine foramen on its inner wall.


Fig. 161. — The Infratemporal and Pterygo-palatine Fossae.



The foramina which open into the pterygo-palatine fossa are three n the posterior wall , in the following order from above downwards, nd from without inwards: the foramen rotundum for the maxillary .erve, the pterygoid canal for the artery and nerve of pterygoid canal, nd the palatino-vaginal canal for the pharyngeal artery and the pharyneal branch of the spheno-palatine ganglion. On the medial wall is he spheno-palatine foramen for the spheno-palatine branches of spheno>alatine ganglion and the spheno-palatine artery. Inferiorly is the •pening of the greater palatine canal for the greater palatine nerve ,nd the greater palatine artery. In this situation there may also be he openings of the lesser palatine canals for the lesser palatine arteries .nd nerves, but these openings usually branch off from the main canal. interiorly is the infra-orbital fissure. Laterally the fossa communiates with the infratemporal fossa through the pterygo-maxillary fissure.

5. The Lower Surface of Base of Skull.

The external surface of the base of the skull (norma basilaris), from vdiich the mandible is excluded, is very irregular, and presents three livisions—anterior, middle, and posterior.

The anterior division forms the hard palate, and resembles a horsehoe. It is bounded in front and laterally by the alveolar arches of he maxillae, and behind by the posterior borders of the horizontal )lates of the palatine bones. The posterior border presents in the niddle line the posterior nasal spine in two halves, from which the nusculus uvulae arises. At either side of this it is sharp and concave or the attachment of the soft palate. The bones forming the hard >alate are the palatine processes of the maxillae over the anterior threeourths, and the horizontal plates of the palatine bones over the poserior fourth. The surface is vaulted, and is intersected by two sutures, niddle palatine and transverse palatine. The middle palatine suture ixtends from the alveolar point to the posterior nasal spine, and indices the meeting of the palatine processes of the maxillae and palatine )ones of opposite sides. The transverse palatine suture crosses the niddle one at right angles about | inch in front of the posterior border, ind laterally it turns backwards to end at the greater palatine foramen.

It indicates the meeting of the palatine process of the maxilla and the horizontal plate of the palatine bone of either side.

In young skulls two additional sutures are present, called maxillo)remaxillary, each of which extends from the posterior part of the ncisive fossa to the interval between the lateral incisor and canine eeth. Each of these sutures corresponds with the place of junction )f the maxilla proper and the premaxilla.

The hard palate presents several openings. At the anterior exremity of the middle palatal suture is the diamond-shaped incisive ossa. Within this are four openings, two being placed laterally, one it either side, called the lateral incisive foramina, and two in the median ine in the intermaxillary suture, called the median incisive foramina,



Fig. 162. — The Ex

1. Incisive Fossa

2. Post. Nasal Spine

3. Post. Border of Vomer

4. Facial Surf, of Maxilla

5. Pterygoid Hamulus of Medial

Pterygoid Plate of Sphenoid

6. Pterygoid Fossa

7. Lateral Pterygoid Plate

8. Temporal Process of Malar

9. Zygomatic Process of Temporal

10. Pharyngeal Tubercle (pointer crosses Foramen Lacerum)

11. Groove for Pharyngo-Tympanic Tube

12. Groove for Chorda Tympani Nerve

13. Petrous Portion of Temporal (Origin of Levator Palati)

14. Carotid Canal

15. Ext. Auditory Meatus

16. Ext. Auditory Process

17. Basion


ernal Surface of the

18. Mastoid Process

19. Jugular Foramen

20. Anterior Condylar Canal

21. Mastoid Notch

22. Occipital Groove

23. Posterior Condylar Canal

24. Superior Nuchal Line

25. Inferior Nuchal Line

26. Ext. Occipital Crest

27. Ext. Occipital Protuberance

28. Opisthion

29. Foramen Magnum

30. Right Occipital Condyle

31. Foramen Lacerum

32. Vagina] Proc. of Tymp. Plate

33. Mastoid Foramen

34 - Stylo-Mastoid Foramen

35. Styloid Process

36. Tympanic Plate (Post, part of

Articular Fossa)

37 - Spine of Sphenoid


Base of the Skull.

38. Ant. part of Articular Fossa

39. Foramen Spinosum

40. Foramen Ovale

41. Emissary Sphenoidal Foramen

42. Tubercle of Root of Zygoma

43. Articular Eminence

44. Infratemporal Fossa

45. Infratemporal Crest

46. Temporal Division of Greater

Wing of Sphenoid

47. Infra-Orbital Fissure.

48. Maxillary Tuberosity

] Lesser Palatine Foramina

51. Greater Palatine Foramen

52. Right Posterior Bony Aperture

of Nose (pointer crosses ridge for Tensor Palati)

53 - Groove for Greater Palat. Artery

54 - Horiz. Plate of Palatine Bone 55. Palat. Proc. of Maxilla


interior and posterior respectively. Each of the former transmits a branch of the greater palatine vessels from the palate to the nasal ossa, whilst each of the latter transmits the long spheno-palatine nerve

rom the nasal fossa to the hard palate, the anterior, which usually )pens from the left nasal fossa, containing the left nerve, and the posterior , which usually opens from the right nasal fossa, containing the right nerve. Medial to the last molar socket at either side is the greater palatine foramen, which is the outlet of the greater palatine ranal, and through which the greater palatine nerve and the greater Dalatine vessels pass. Leading forwards from this foramen there is a groove for the transmitted structures. A little behind the greater Dalatine foramen are the lesser palatine foramina for the lesser palatine lerves. There are usually two such foramina, medial and lateral, but the latter one is inconstant. Besides the foregoing openings, there are 1 number of nutrient foramina. Over its posterior third the hard Dalate presents several depressions for the palatine mucous glands, and extending inwards from the back part of the greater palatine foramen it either side is a transverse ridge, which divides the palatine gland and yives partial insertion to the tensor palati muscle. In addition to these the torus palatinus, described on p. 216, may occasionally be seen.

The middle division extends from the posterior border of the hard palate to a transverse line on a level with the anterior margin of the foramen magnum. Laterally it is limited by a line extending from the tuberosity of the maxilla to the styloid process of the temporal. It is on a higher level than the anterior division, and its central or basilar part is sometimes termed the guttural fossa. The bones forming it at either side are the tubercle of the palatine bone, the pterygoid process, and a small part of the greater wing of the sphenoid, and the inferior surface of the petrous portion of the temporal. The central part is formed by the basilar process of the occipital, the body and vaginal processes of the sphenoid, the superior border and alae of the vomer, and the sphenoidal processes of the palatine bones.

Anteriorly it presents the posterior bony apertures of the nose, already described, and at either side of these openings is the pterygoid fossa, which is bounded medially by the medial, and laterally by the lateral, pterygoid plate of the sphenoid, the fossa being completed interiorly by the tubercle of the palatine bone.

In a line extending backwards and outwards from the lateral pterygoid plate to the styloid process the following parts are seen, in order from before backwards: foramen ovale; foramen spinosum ; spine of the sphenoid; medial border of the tympanic plate of the temporal, forming posteriorly the vaginal process ; and styloid process. Inside the foregoing line anteriorly is the groove for pharyngo-tympanic tube, which lies obliquely between the greater wing of the sphenoid and the apical part of the petrous portion of the temporal. This groove lodges the cartilaginous part of the pharyngo-tympanic tube, and, when followed outwards and backwards, it leads to the pharyngo-tympanic canal in the angle between the squamous and petrous portions of the temporal.

On either side of the basilar process of the occipital is the foramen lacerum. It lies between the basilar process, the apex of the petrous portion of the temporal, and the greater wing of the sphenoid near the root of the pterygoid process. In the recent state it is closed below by cartilage, which is pierced by a meningeal branch of the ascending pharyngeal artery, one or more emissary veins from the cavernous sinus, and partly by the greater superficial petrosal nerve and internal carotid artery, which lie in the space but do not traverse it completely.

In a line extending backwards and outwards from the foramen lacerum are the following markings on the inferior surface of the petrous portion of the temporal: the rough surface from which the levator palati and tensor tympani arise; the carotid canal, which transmits the internal carotid artery and the ascending branch of the superior cervical ganglion of the sympathetic; a minute foramen, on the posterior wall of the vertical portion of the carotid canal, for the carotico-tympanic branch of the carotid sympathetic plexus and carotico-tympanic branch of the internal carotid artery; the jugular fossa, which forms part of the jugular foramen; the tympanic canaliculus, on the ridge between the carotid canal and jugular fossa, for the tympanic branch of the glosso-pharyngeal and the tympanic branch of the ascending pharyngeal artery; and the mastoid canaliculus, on the outer wall of the jugular fossa, for the auricular branch of the vagus. Between the petrous portion of the temporal and the jugular process of the occipital is the jugular foramen, which lodges the commencement of the internal jugular vein, and transmits the following structures: the glosso-pharyngeal, vagus, and accessory nerves; the inferior petrosal sinus; and meningeal branches of the ascending pharyngeal and occipital arteries.

Lateral to the front of the occipital condyle is the anterior condylar canal for the hypoglossal nerve and a meningeal branch of the ascending pharyngeal artery. I he under surface of the basilar process of the occipital presents the pharyngeal tubercle.

The posterior division is limited in front by a transverse line on a level with the anterior margin of the foramen magnum, and behind by the external occipital protuberance and the superior nuchal line at either side. It is formed by the supra- and ex-occipital portions of the occipital, and the mastoid portions of the temporal bones.

In the middle line is the foramen magnum, which transmits the central nervous axis and its membranes, the accessory nerves, the vertebral arteries, the anterior spinal and posterior meningeal arteries, parts of the cerebellar amygdalae, and the membrana tectoria. The centre of the anterior margin of the foramen magnum is known as the basion, and the centre of the posterior margin as the opisthion. Proceeding outwards from this foramen are the occipital condyle, jugular process, occipital groove for the occipital artery, mastoid notch for the posterior belly of the digastric, and the mastoid process. Behind the occipital condyle is the condylar fossa, in which there may be a posterior condylar canal for the passage of an emissary vein from the sigmoid inus. Behind the foramen magnum is the supra-occipital portion of he occipital, which presents the external occipital crest in the median ine, and the inferior nuchal line extending outwards on either side from ts centre; while in or close to the suture between the mastoid and upra-occipital bones there may be a mastoid foramen transmitting an missary vein from the transverse sinus and a meningeal branch of the >ccipital artery.

The Interior of the Cranium.

A sagittal or antero-posterior section of the skull a little to one iide of the median plane shows the nasal septum already described.


Fig. 163. — Sagittal Section of the Skull to the Right of the Median Plane.

F, frontal; P, parietal; O, occipital; T, temporal.


1. Coronal Suture

2. Anterior and Posterior Menin geal Grooves

3. Lambdoid Suture

4. Subarcuate Fossa

5. Sigmoid Groove

6. Inion (External Occipital Pro tuberance)

7. Asterion

8. Sigmoid Groove

9. Aqueduct of Vestibule o. Jugular Foramen

11. Anterior Condylar Canal

12. Internal Auditory Meatus

13. Styloid Process

14. Dorsum Sellae

15. Sella Turcica

16. Lateral Pterygoid Plate

17. Pterygoid Hamulus

18. Superior Nasal Concha

19. Superior Meatus

20. Inferior Meatus

21. Right Maxilla

22. Anterior Nasal Spine

23. Inferior Nasal Concha

24. Middle Meatus

25. Middle Nasal Concha

26. Infundibulum

27. Nasal Bone

28. Right Sphenoidal Sinus

29. Right Frontal Sinus

30. Crista Galli

31. Optic Foramen

32. Pterion


Vlong, and at either side of, the vault of the cranium is the groove for

he superior sagittal venous sinus, which extends from before back


wards, and on either side of its parietal portion are the pits for arachnoid granulations. The internal openings of the parietal foramina may be seen, as well as the branching system of meningeal grooves and impressions for cerebral gyri. The basi-cranial, basi-facial, and basibregmatic axes are to be studied from this section. The basi-cranial axis represents a line drawn upwards and forwards from the basion to the spheno-ethmoidal suture. The basi-facial axis corresponds with a line drawn from the spheno-ethmoidal suture to the subnasal point. The angle formed by these two axes is known as the cranio-facial angle. The basi-bregmatic axis represents a line drawn vertically from the basion to the bregma.

The most instructive coronal or transverse section is one made in the plane of the basi-bregmatic axis. Such a section gives important views of the parts within the petrous portion of the temporal, such as the external auditory meatus, tympanic cavity, and vestibule.

When a horizontal section has been made on a level with the occipital point and the most prominent part of the glabella, the vaulted roof of the cranium is removed. This is called the calvaria, or skullcap, and it is formed by portions of the frontal, parietals, squamous portions of the temporals, and occipital. The outer plate is strong, except over the temporal region, but the inner is brittle and readily cracked, from which circumstance it is known as the vitreous (glassy) plate. Between the two plates there is cancellated tissue, here called diploe. The interior of the calvaria presents branching meningeal grooves, impressions for cerebral gyri, and along the middle line the groove for the superior sagittal venous sinus, with depressions at either side for the arachnoid granulations. The openings of the parietal foramina may be noted. The simple structure of the sutures of the vault when seen from the intracranial aspect has been called attention to already.

The Intracranial Surface of the Base of the Skull.

The base forms the floor of the cranial cavity, and is of very irregular outline and thickness. The thickest and densest parts are the petrous portions of the temporals. The mastoid portion of the temporal and the basilar part of the occipital are also thick. The thinnest parts are the cribriform plate of the ethmoid and the orbital plates of the frontal, but the central portions of the cerebellar fossae of the occipital are also thin, sometimes remarkably so. The interior of the base is divided into three fossae—anterior, middle, and posterior.

Anterior Fossa.—The floor of this fossa is formed by the orbital plates of the frontal, the cribriform plate of the ethmoid, and the lesser wings, jugum sphenoidale, and ethmoidal spine of the sphenoid. It is limited posteriorly by the posterior border of the lesser wing of the sphenoid at either side, and by the limbus sphenoidalis in the centre. It is subdivided into a central and two lateral parts.

The central portion, which is depressed, is formed by the cribriform plate of the ethmoid and the ethmoidal spine and jugum of the sphenoid. In the middle line it presents the crista galli, which gives attachment to the falx cerebri. In front of this is the foramen caecum, which, when pervious, transmits an emissary vein passing between the intracranial superior sagittal sinus and the veins of the roof of the nose. At each side of the crista galli are the nasal slit for the anterior ethmoidal artery and nerve; the olfactory foramina for the filaments of the olfactory bulb; the cranial opening of the anterior ethmoidal foramen for the anterior ethmoidal artery and nerve; and the cranial opening of the posterior ethmoidal foramen for the posterior ethmoidal artery and nerve. The last two openings are situated at the outer side of the cribriform plate, lateral to the olfactory groove which marks it. Directly beneath each half of the cribriform plate is the corresponding nasal fossa.

Each lateral portion of the anterior fossa is irregularly convex, and forms the roof of the orbit. It is formed by the orbital plate of the frontal and the lesser wing of the sphenoid. It is very thin, and, except over the lesser wing of the sphenoid, it presents digitate impressions for the convolutions of the orbital surface of the frontal lobe of the cerebrum, which it supports. The sutures in the anterior fossa are the fronto-ethmoidal, fronto-sphenoidal, and spheno-ethmoidal.

Middle Fossa. —This fossa is on a lower level than the anterior. It is bounded in front by the posterior border of the lesser wing of the sphenoid at either side, and by the limbus sphenoidalis in the centre. Behind, it is limited by the superior border of the petrous portion of the temporal at either side, and by the dorsum sellae of the sphenoid in the centre. It presents a central and two lateral divisions. The central division is formed by the superior surface of the body of the sphenoid, posterior to the limbus sphenoidalis. Each lateral division, which is much depressed, is formed anteriorly by the superior surface of the greater wing of the sphenoid, laterally by part of the squamous portion of the temporal, and posteriorly by the superior surface of the petrous portion of that bone. It lodges the temporal lobe of the cerebrum, and it presents the following sutures: the spheno-parietal; squamous; squamo-sphenoidal; and petro-sphenoidal.

The central division presents the following parts: the optic groove and tuberculum sellae ; the optic foramen of each side for the optic nerve and ophthalmic artery; the anterior clinoid process of each side; the sella turcica or hypophysial fossa for the hypophysis; the carotid groove, at either side of the sella turcica, for the cavernous venous sinus and internal carotid artery, the latter being accompanied by the cavernous sympathetic plexus of nerves, and having the sixth cranial nerve on its outer side; the middle clinoid process of each side (sometimes connected with the anterior, which it faces); the dorsum sellae ; the posterior clinoid process of each side, at either lateral angle of the dorsum sellae; and the groove for the inferior petrosal sinus, on each side of the dorsum sellae a little below the posterior clinoid process. The central division corresponds with the interpeduncular region at the base of the cerebrum.


Fig. 164. — The Intracranial Base of the Skull.

The superior surface of the petrous portion of the right temporal bone has

Deen removed to expose the internal auditory meatus and semicircular canals.


1. Foramen Cagcum

2. Crista Galli

3 - Ethmoidal Spine of Sphenoid

4 - Jugum Sphenoidale

5 - Anterior Fossa

6. Limbus Sphenoidalis 7- Optic Groove 8 . Tuberculum Sellas 9 • Posterior Border of Lesser Wins' of Sphenoid

10. Anterior Clinoid Process

11. Middle Clinoid Process

12. Sella Turcica

I 3 - Posterior Clinoid Process 14. Dorsum Sellse 15 - Clivus

16. Groove for Inf. Petrosal Sinus

17. Superior Semicircular Canal 10. Lateral Semicircular Canal

19. Posterior Semicircular Canal Meatus


20. Internal Auditory Meatus (laid open)

21. Opening of Internal Auditory

22. Anterior Condylar Canal

23. Basion

24. Groove for Transverse Sinus

25. Vermian Fossa

26. Confluence of the Sinuses

27. Int. Occipital Protuberance

28. Internal Occipital Crest

29. Opisthion

30. Cerebral Fossa

31. Cerebellar Fossa

32 . Jugular Foramen

33 - Sigmoid Groove

34 - Internal Auditory Meatus

35 - Trigeminal Impression

36. Arcuate Eminence

37. Hiatus for Greater Superficial Petrosal Nerve


38. Hiatus for Lesser Superficial Petrosal Nerve

39. Foramen Lacerum

40. Foramen Spinosum

41. Foramen Ovale

42. Middle Fossa

43. Emissary Sphenoidal Foramen

44. Lingula of Sphenoid

45. Parietal Bone

46. Coronal Suture

47. Carotid Groove

48. Pterion

49. Foramen Rotundum

50. Orbital Plate of Frontal

51. Superior Orbital Fissure

52. Carotid Notch

53. Optic Foramen

54. Posterior Ethmoidal Foramen

55. Anterior Ethmoidal Foramen

56. Left Frontal Sinus








Each lateral division is marked by meningeal grooves and impressions for cerebral gyri, and presents the following openings: the superior orbital fissure for the third cranial nerve, the fourth, the three branches of the ophthalmic division of the fifth (namely, frontal, lacrimal, and naso-ciliary), and the sixth cranial nerves, the sympathetic root of the ciliary ganglion, the superior ophthalmic veins, the orbital branch of the middle meningeal artery, and a portion of the dura mater to form the orbital periosteum; the foramen rotundum, leading to the pterygo-palatine fossa, and transmitting the maxillary division of the fifth cranial nerve; the foramen ovale, leading to the infratemporal fossa, and transmitting the mandibular division and the motor root of the fifth cranial nerve, the accessory meningeal artery, the middle meningeal vein, an emissary vein from the cavernous sinus, and occasionally the lesser superficial petrosal nerve; the accessory sphenoidal foramen (inconstant), leading to the scaphoid fossa at the root of the medial pterygoid plate, or to the pterygoid fossa lateral to the scaphoid fossa, and transmitting an emissary vein from the cavernous sinus; the foramen spinosum, leading to the infratemporal fossa, and transmitting the middle meningeal artery and the nervus spinosus branch of the mandibular nerve; and the foramen lacerum, situated between the basilar process of the occipital, the apex of the petrous portion of the temporal, and the greater wing of the sphenoid near the root of the pterygoid process. The posterior opening of the pterygoid canal, which leads to the pterygo-palatine fossa and transmits the nerve and artery of pterygoid canal, is to be found on its anterior wall, while the carotid canal for the internal carotid artery, with a plexus of sympathetic nerve fibres, opens on its lateral wall.

The anterior surface of the petrous portion of the temporal presents, in addition to the impressions produced by the overlying convolutions of the temporal lobe of the brain, the following markings: the trigeminal impression, near the apex, for the trigeminal ganglion; the hiatus for greater superficial petrosal nerve, to which a groove conducts the greater superficial petrosal nerve and the petrosal branch of the middle meningeal artery (within this opening there may be a small one for the external superficial petrosal nerve); the hiatus for lesser superficial petrosal nerve, to which a groove conducts the lesser superficial petrosal nerve; the arcuate eminence, which coincides with the position of the superior semicircular canal of the internal ear; and the tegmen tympani.

Posterior Fossa. —This fossa is on a lower level than the middle. It is limited in front by the dorsum sellae of the sphenoid in the centre, and the superior border of the petrous portion of the temporal at either side. Behind it is limited by the internal occipital protuberance and the groove at either side for the transverse venous sinus, which groove also marks its lateral extent. It lodges the pons, medulla oblongata, and cerebellum. The bones which form it are as follows: the dorsum sellae of the sphenoid; the basilar, condylar, and supraoccipital portions of the occipital; the petrous and mastoid portions of the temporal; and the postero-inferior angle of the parietal. It presents the following sutures: the occipito-mastoid; parieto-mastoid; and petro-basilar. The following parts are to be noted: the clivus, the upper part of which lodges the pons and basilar artery, whilst the lower part contains the medulla oblongata; the foramen magnum, which transmits the medulla oblongata and its membranes, the accessory nerves, and the vertebral, anterior spinal, and posterior spinal arteries; the anterior condylar canal, on either side of the foramen magnum, for the hypoglossal nerve and a meningeal branch of the ascending pharyngeal artery; the internal occipital crest, which gives attachment to the falx cerebelli, and is occasionally grooved for the occipital venous sinus (near the foramen magnum this crest presents the vermian fossa, which receives a part of the vermiform process of the cerebellum); the cerebellar fossae, which lodge the hemispheres of the cerebellum; the opening of the internal auditory meatus, on the posterior surface of the petrous portion of the temporal, for the motor and sensory roots of the facial nerve and the auditory nerve, and the internal auditory artery; the aqueduct of vestibule, about J inch lateral to the preceding, for a small artery and vein, and the endolymphatic duct, the subarcuate fossa, representing the parafloccular fossa of early life, situated close to the superior border of the petrous portion, about midway between the opening of the internal auditory meatus and aqueduct of vestibule; and the jugular foramen, between the jugular process of the occipital and petrous portion of the temporal.

The jugular foramen is divided into three compartments, which lie obliquely from behind forwards and inwards. The postero-lateral compartment transmits the transverse venous sinus to become the internal jugular vein, and a meningeal branch of the ascending pharyngeal artery; the middle compartment transmits the glosso-pharyngeal, vagus, and accessory nerves; and the antero-medial compartment gives passage to the inferior petrosal venous sinus. The antero-medial compartment may be more or less completely isolated by means of the intrajugular process passing between the occipital and the petrous portion of the temporal.

the posterior fossa is grooved by the following venous sinuses: the transverse sinus, which extends from the internal occipital protuberance to the jugular foramen, grooving in its sinuous course the squamous part of the occipital, the postero-inferior angle of the parietal, the mastoid portion of the temporal, and the jugular process of the occipital (opening from which there is usually the mastoid foramen, and occasionally the posterior condylar canal); in its descending course it is often spoken of as the sigmoid sinus, and it is worth noticing that a hole drilled from outside the skull, 1 inch behind the middle of the top of the external auditory meatus, will just strike the groove for the sinus as it is making its turn downward; the superior petrosal sinus, which grooves the superior border of the petrous bone; the inferior petrosal sinus, along the course of the petro-basilar suture; and the occipital sinus, which sometimes grooves the internal occipital crest.


Sutural Bones

The sutural bones (originally named after Wormius) are accessory bones which are frequently met with in the course of the cranial sutures, and occasionally in the face, as in the region of the lacrimal bones, and at the outer extremity of each inferior orbital fissure. From their position in the course of sutures they are known as ossa suturarum. They are for the most part of small size and triangular outline, and are hence sometimes spoken of as ossa triquetra. They are usually due to the appearance of special ossific centres. Their most common situation is along the course of the lambdoid suture, where they may form a regular chain. The superior angle of the occipital sometimes persists as a sutural bone, called pre-interparietal, which may be double. One is often found between the antero-inferior angle of the parietal and greater wing of the sphenoid in the region of the pterion, and it is known as the epipteric bone. If the metopic or frontal suture is persistent, one or more sutural bones may be present along its course, and if at the upper part, they may give rise by their persistence-and union to a bregmatic bone. In the condition known as chronic hydrocephalus sutural bones of large size are present in great numbers along the cranial sutures.


The Skull at Birth

The skull at birth is remarkable for its large size, and for the great development of the cranium as compared with the face. The face is equal to one-eighth of the cranium, whereas in the adult it is equal to one-half. The occipital, parietal, md frontal regions are well developed, the parietal and frontal eminences are very conspicuous, md the mastoid processes are absent. The bones are not united by sutures, but are connected by fibrous tissue, continuous with the periosteum externally and dura mater internally. Membranous intervals exist between the angles of certain bones, these being called fontanelles, from the pulsation, or welling-up sensation, which can be felt there. They are six in number, two being placed in the median line, anterior and posterior, and two at either side, anterolateral and postero-lateral. The anterior fontanelle is situated between the antero-superior angles of the parietals and the superior angles of the two halves of the frontal. It is large and diamond-shaped, and it is


Fig. 165. — Skull at Birth (Anterior Aspect).


not completely closed, as a rule, until towards the end of the second year. The posterior fontanelle is situated between the postero-superior angles of the parietals and the superior angle of the occipital. It is small and triangular, and is usually closed at, or shortly after, birth, but the surrounding bones are still movable. The antero-lateral and postero-lateral fontanelles correspond with these angles of the parietal. The antero-lateral is situated between the parietal, sphenoid, frontal, and squamous portion of the temporal, whilst the postero-lateral is situated between the parietal, occipital, and mastoid portion of the temporal. For the sagittal fontanelle of the earlier part of foetal life, see Parietal Bone.

The facial appearances in the foetal skull are the results of the conditions of the upper and lower jaws, and of the rudimentary teeth carried by them: these last are within the jaws, so that their height (when erupted) is lost to the face. The maxillae are flattened, the maxillary sinus being present only as a very small cavity near the mesial part of the body of the bone. It follows from this that the palate level is not much below that of the orbital floor, and the lower part of the nasal cavity on each side is small. The ethmoidal portion of the cavity, on the other hand, is of proper proportionate size. Associated with the maxillary condition is a low height for the perpendicular part of the palatine bone, and for the vomer. The mandible does not possess a definite angle, and is in two halves, meeting at the symphysis. The maxillary height increases markedly with the temporary dentition, and especially with the permanent dentition; the increase is associated with growth of the sinus and eruption of teeth, lowering of the level of the nasal floor, with relative increase in nasal height, growth in depth of palatine and vomer, and a more oblique plane of the posterior nasal openings.

The lateral aspect of the foetal skull shows the maxillary and mandibular conditions mentioned above, the low level of the zygomatic bone and arch being associated with these. In addition the temporal bone is seen to possess neither mastoid process nor tympanic part: tnib latter plate is represented here by a ring, to which the membrane



Fig. 166. — The Skull at Birth, showing the Anterior and Posterior Fontanelles, and the Parietal Eminences.


5 attached. The absence of a mastoid process leads to the exposure n the lateral aspect of the digastric groove and the foramen for the xit of the facial nerve. The process begins to project during the econd year: the tympanic ring begins its extension into a ' plate ’ luring the first year.

The tympanic membrane, being attached to a ring, with no proection of bone from this, is therefore visible on the side of the skull, t must not be imagined, however, that it is visible in that way in the omplete head, for the external auditory meatus is as long proporionately in the child as in the grown-up person: it is only in the bony >art of its floor that it is deficient.

The skull increases rapidly in size during the first six years, and further marked increase commences on the approach of puberty, idiich is associated with the development of the cranal air sinuses.


Fig. 167. — The Skull at Birth, showing the Antero-lateral and POSTERO-LATERAL FONTANELLES.

The latter increase affects chiefly the frontal and facial regions. In Id age the cranial bones become thinner, the cranial air sinuses undergo nlargement, and the sutures show indications of obliteration.

Characters of the Female Skull.—The skull is smaller, smoother, nd lighter than in the male, the bones are not so thick, the external ccipital protuberance, mastoid processes, and supra-orbital processes re feebly developed. The frontal eminences, on the other hand, re often better developed than in the male, and the orbital openings iss compressed from above downward. The teeth, jaws, and chin re slighter, and in individuals of the same race the female skull is ader in comparison with its length— i.e., more brachycephalic—than le male. In spite of these differences there is reason to believe that ae most experienced craniologists can only determine the sex of bout seven out of ten skulls with certainty, because before puberty differentiation has hardly occurred; while, after the menopause, female skulls tend to assume the male characteristics. For this reason it is very important to take the age into account in determining sex.

Racial Peculiarities of the Skull.

In comparing the skulls of different races, attention has to be directed to the following points: the capacity of the cranium, its circumference, its relative length, breadth, and height; the degree of forward elongation of the jaws; and the shape of the anterior nasal and orbital apertures. The cranial capacity may be ascertained by filling the skull with shot, or various kinds of seeds, and then measuring the contents in a graduated vessel. The capacity ranges from about 1,200 to i,600 c.c., and, according to their capacity, skulls are divided into three groups: macrocephalic, with a capacity exceeding 1,450 c.c., as in Europeans; microcephalic, with a capacity under 1,350 c.c., as in Australians; and mesocephalic, between 1,350 and 1,450 c.c., as in Chinese.

In regard to craniometry, the following craniometrical terms may here be summarized:

Alveolar point=the point of meeting of the anterior margins of the alveolar borders of the maxillae.

Antinion=the most prominent point of the glabella.

Asterion=the point where the parieto-mastoid, occipito-mastoid, and lambdoid sutures meet.

Auricular point^the centre of the opening of the external auditory meatus.

Basion=the centre of the anterior margin of the foramen magnum.

Bregma=the point of junction of the sagittal and coronal sutures.

Dachryon=the point where the horizontal fronto-maxillary suture meets the vertical lacrimo-maxillary suture.

Entomion=the point near the anterior part of the parieto-mastoid suture, where a process of the parietal is received into the parietal notch of the mastoid

Glabella=a point midway between the superciliary arch of the frontal.

Gnathion, or mental point=the middle point of the anterior lip of the lower border of the mandible.

Gonion=the outer side of the angle of the mandible.

Inion =the external occipital protuberance.

Jugal point =a point situated at the angle which the posterior border of the frontal process of the zygomatic forms with the superior border of its temporal process.

Larnbda=the meeting of the sagittal and lambdoid sutures.

Nasion, or nasal point=the meeting of the two fronto-nasal sutures.

Obelion=the point where the horizontal line connecting the parietal foramina intersects the sagittal suture.

Occipital point=the part of the occipital in the median plane at the greatest distance from the glabella.

Ophryon=the centre of a line drawn from one temporal line to the other across the narrowest part of the frontal region.

Opisthion=the centre of the posterior margin of the foramen magnum.

Pterion=the region of the spheno-parietal suture.

Rhinion=the lower part of the internasal suture.

Stephanion=the point where the superior temporal line crosses the coronal suture.

Subnasal point=the centre of the base of the anterior nasal spine.

The horizontal circumference of the cranium represents the measurement at the level of a plane passing through the most prominent part of the glabella m front, the pterion laterally, and the occipital point behind.

the greatest length represents the measurement from the most prominent part of the glabella to the occipital point. The greatest breadth represents he transverse measurement, but it should be indicated whether this happens o be biparietal or bisquamous. The proportion of greatest breadth to greatest ength is the index of breadth, or cranial index. In civilized races about 190 mm. •epresents an average length, and about 148 mm. an average breadth. Accordng to their cranial index, skulls are arranged in three classes—namely, brachyjephalic (broad and short), with a cephalic index over 80, as in mid-Europeans Alpine race); mesaticephalic (intermediate), with an index of 75 to 80, as in SForthern and Southern Europeans and Chinese; and dolicocephalic (long and larrow), with a cephalic index below 75, as in Anglo-Saxons and most Africans.

The height of the skull represents the measurement from the basion to the Dregma, and its proportion to the length is the index of height, or vertical index, [ts average in civilized races corresponds with the breadth. Since it is obviously mpossible to take this measurement in the living, modern craniologists replace t by, or supplement it with, the biauricular height, which, unfortunately, needs 1 special craniometer.

The longitudinal arc of the skull represents the measurement from the nasion to the opisthion carried over the roof, and the basi-nasal length represents the neasurement from the basion to the nasion. These two measurements, plus

he distance between the basion and the opisthion, represent the vertical cir:umference of the cranium in the median plane. The degree of projection )f the jaws is ascertained from the gnathic or alveolar index. This index represents the proportion of the basi-alveolar length to the basi-nasal. According

o the gnathic index, skulls are arranged in three classes—namely, orthognathous straight and upright jaw), with a gnathic index below 98, as in Europeans; nesognathous (intermediate in character), with an index of from 98 to 103, is in Chinese and Japanese; and prognathous (projecting jaw), with an index >ver 103, as in Australians.

Here, again, any comparison between the living head and the dry skull is mpossible, and in order to meet this, the auricular point is often substituted or the basion.

The form of the anterior nasal aperture is ascertained from the nasal index.

rhis represents the proportion of the greatest transverse measurement of the iperture to the height, which latter is the measurement from the nasion to the

ubnasal point. According to their nasal index, skulls are arranged in three lasses—namely, leptorhine (narrow nose), with a nasal index below 48, as in Europeans; mesorhine (intermediate nose), with an index of from 48 to 53, as n Chinese and Japanese; and platyrhine (broad nose), with an index above 53, is in Australians and Kaffirs.

The form of the orbital aperture is ascertained from the orbital index, which epresents the proportion of the height to the width of the orbital aperture, rhere are three varieties of orbital index—namely, megaseme (high index), vhen it exceeds 89, as in the Chinese; mesoseme (intermediate index), when t is between 89 and 84, as in Europeans; and microseme (low index), when it s below 84, as in Australians.

Many modern craniologists are not at all satisfied with the value of orbital ind nasal indices, and consider that much more information can be obtained rom the average of the actual heights and widths. The whole subject of scientific

raniology is at present in its infancy, and many factors, such as the range of variation, which cannot be discussed here, have to be taken into account. It hould be realized that the most expert craniologist can only occasionally Letermine the race to which a special skull belongs.

Deformities of the Skull.

The most common cause of cranial deformities is premature synostosis or isseous union of bones which are normally separate, the result being closure »r obliteration of certain sutures. When the sagittal suture becomes premaurely obliterated transverse growth is arrested, and, to compensate for this increased growth takes place at the coronal and lambdoid sutures. The anteroposterior diameter of the cranium is greatly increased, and the vault assumes a boat-like shape. This variety is known as scaphocephaly. When the coronal suture becomes prematurely obliterated, increased growth takes place upwards, and the vertical diameter is greatly increased. This variety is known as acrocephaly (pointed head). When one-half of the coronal or lambdoid suture becomes prematurely obliterated, oblique deformity takes place, this form being known as plagiocephaly (oblique or awry head). When the metopic or frontal suture becomes prematurely obliterated, growth is arrested in the frontal region, and the skull assumes a triangular shape. This variety is known as trigonocephaly. When premature obliteration of the sutures at the base of the skull takes place, the deformity known as cretin skull results. This is characterized by enlargement of the cranium (except in the occipital region), which becomes very heavy, and assumes an irregular, somewhat conical shape, with the apex at the sagittal suture. It is associated with mental dulness, idiocy, and stunted growth, and the general condition is known as cretinism.

When the occipital region bulges markedly the condition is known as bathrocephaly. The above description is based on observations of the developing skulls.


Development of Skull

For purposes of description the skull is divided into cranial and facial parts. This division also corresponds in a general way with differences in developmental origin, the cranial skeleton being formed in the paraxial mesoderm, while the facial skeleton develops in mesoderm derived from the visceral arch structures. The developmental and descriptive divisions do not quite correspond, however, as will become apparent.

A. Cranial Development

This can be divided into membranous , cartilaginous , and bony stages.

1. Membranous.—The hind-brain is surrounded by paraxial mesoderm, and this layer, carried forward round the mid-brain and the projecting fore-brain, forms their immediate covering. The membranes of the brain are developed from the deeper parts of this layer.

2. Cartilaginous.—The paraxial covering begins to show points of chondrification during the fifth week; these points are only in its lower part on the ventral surface of the brain. Formation of actual embryonic cartilage is, of course, a later occurrence, and the condition in the fifth week is really one of development of ‘ prechondral ’ centres. From these points the central basal cartilage is formed.

The relation of the notochord to the base of the skull varies in different animals. In man it lies below the basis cranii, in relation with the pharynx, turning up to enter the postsphenoid region just behind the hypophysial fossa, where it ends. The cartilaginous base, however, although it lies above the notochord, can be quite properly termed ‘ parachordal/

The cartilaginous basis cranii, developed from these beginnings in the paraxial mesoderm, has certain definite original regions, the arrangement of which can be understood best by gaining a preliminary acquaintance with those seen in a primitive skull. A general scheme of such primitive chondro-cranial structure is given in Fig. 168, showing two stages. In the first the notochord, placed centrally, extends forward is far as the pituitary or hypophysial space, occupied by the infundibular growth from the fore-brain. On each side of the notochord are cartilaginous plates—hence termed parachordal plates. Two cartilaginous Dars extend forward, on each side of the pituitary space, from the lotochord area: these bars are therefore prechordal. Thus the middle Dart of the cartilaginous base is made up of a parachordal part (behind

he hypophysial space) and a prechordal part (in front of the space). But the chondrification of these areas does not extend very far laterally, md here we find on each side the organs of special sense, embedded


Fig. 168. — Diagrams of the Primitive Cartilaginous Cranium (Wiedersheim).

C First Stage.—N, notochord; PchC, parachordal cartilage; Tr, prechordal cartilage; PPS, primitive hypophysial space; Olf, Opt, And, positions of organs of smell, sight, and hearing.

3 . Second Stage.—N, notochord; PchR, parachordal region (basilar plate); TrR, fusion of prechordal cartilages; PPS, primitive hypophysial space; TrR, prechordal region; Olf, Opt, Aud, as in A.

n paraxial mesoderm: the auditory organ on each side lies beside the )arachordal cartilage, the eye beside the prechordal bar, and the olfacory organ in antero-lateral relation to the same bar.

In the second stage shown in the figure the parachordal and prehordal cartilages have united into a continuous plate, pierced by the lypophysial foramen anterior to the end of the notochord. In addition here are indications of cartilaginous formations associated with the pedal sense capsules: in the olfactory region, for example, the >rechordal plate is prolonged forward between the two organs, and a

artilaginous process f walls in ' the organ on each side, separating it rom the eye—thus showing that each region is enclosed in a cartiaginous ‘ olfactory capsule/ A capsule is also formed for the eye, but the immediate surrounding of the globe could not be fixed to the cartilaginous base, and is therefore a variable constituent of the wall of the globe: yet there is a process of cartilage (not shown in figure) which projects (ala orbitalis) from the hinder part of each prechordal cartilage, passing out behind the eye. The auditory organ is surrounded

rapidly by cartilage, forming the otic capsule, which lies thus lateral to the parachordal plate: the two otic capsules quickly fuse with this plate, thus fixing the basal ‘ floor ’ with the ‘ lateral wall,’ to which they belong primitively.

In the highest form of the skull the orbits come to look more forward than laterally, while the nasal cavities are more apically placed. Thus an interval occurs between the orbit (ala orbitalis) in front, and the otic capsule behind, and in this interval a new (visceral) bone, the ala temporalis of the mammalian skull, is inserted: it has no cartilaginous precursor in its greater part, so that the chondro-cranium in such skulls shows an angled interval between the ala orbitalis and the otic capsule.

If the conditions in the human embryo, at the time that the chondrific changes are beginning to appear, are compared with this general primitive state, the corresponding arrangement of the parts becomes evident. Fig. 169 gives a plan of these as they would be in an embryo between 13 and 14 mm. in length, when the prechondral changes in the paraxial mesoderm are beginning to appear: it shows the position of the formations in the base of the cranial cavity, the spinal cord leaving that cavity through A, while the down-turned fore-brain occupies the hollow B. The hypophysial canal is shown as a small black spot (H) a little distance behind the recess for the fore-brain. Between this and the spinal orifice the parachordal bars (P) are seen: they are evidently paired in formation, but will fuse quickly into a simple parachordal plate. The otic capsules (OT) are seen on each side of this, distinct from it, and the internal carotids are seen turning upwards in front of the capsules to enter the cranial cavity.


Fig. 169. — Plan to show the Constituent Parts of the Cranial Base, as seen when Chondrification is beginning at 13 to 14 Mm.

A, spinal foramen ; B, occupied by fore-brain; VN, trigeminal ganglion embedded in parax. mesod.; H, hypophysial foramen; OF, optic foramen; OT, otocyst; P, parachordal cartilage ; XII, hypoglossal ; pl.pl., parietal plate of cartilage extending from otic capsule.



This is the spot where the artery always enters the vertebrate skull: it pierces the dura mater a little in front of this. Observe that the parachordal bars are beginning to extend backwards md laterally, as shown by the arrows: this extension is laying the foundation of the exoccipital and post-occipital. The extension in the figure is fierced by the hypoglossal nerve (XII), and it is likely that there is 1 separate chondral centre for that part lying between the nerve and the margin of the aperture.

Two short ‘ sphenoidal bars ' have the rypophysial foramen between them, and ire evidently representatives of the prechordal bars or of parts of these. They vill join quickly and in their subsequent growth will occlude the passage between Tern.

In front of these and lateral to them ire, on each side, two small chondral centres, medial and lateral to the optic bramina (OF). These small chondriications join round the foramen, extend nedially to become confluent with the enlarging 'prechordal ’ cartilages, and extend gradually laterally into the ridge )f tissue (T) which bounds the recess B lostero-laterally. This is the ala orbitalis, vhich has thus become an extension mtwards from the prechordal cartilage.

Observe that the eye is much farther orward: it is partly seen (OPT) proecting on the surface. The angle previously mentioned is therefore already veil marked, between the ala orbitalis md the otocyst, and shows a deep lepression or sac (VN) which contains he trigeminal ganglion.

The comparison with the primitive ype of Fig. 168 has not presented any lifficulty so far, but the formation of he floor of the recess B, and its relation to the type, are not so traightforward. At this stage there is no chondral formation in front >f the ala orbitalis, so it is not necessary to consider it, and it will be nore conveniently dealt with at a later period.

The prominent curved ridge (T) into which the ala orbitalis extends is placed ietween the fore-brain and mid-brain, so that its free border points toward the nid-brain flexure. The ala orbitalis lies in the anterior part of its base: the reater part of the remainder becomes the tentorium cerebelli. As the cerebral esicles grow back, and the hind-brain is closely flexed, the fold (free except diere the ala orbitalis holds it) is carried back below its vesicle, covering the


Fig. 170. — Cartilaginous Base of Cranium of an Embryo of 18 Mm.


PM, paraxial mesoderm underlying front parts of cerebral vesicles; AC, alicochlear commissure.


trigeminal ganglion and the dorsal aspect of the otic capsule, and thus coming into position.

The distinct parts of the early chondrification quickly join to forn a continuous base, as seen in Fig. 170. The backward growths fron the parachordal plate have not met behind, but have practically com pleted their exoccipital part.

The paraxial mesoderm in which the olfactory region and the ey( are embedded has no chondral formation in the early stages. It lie* in front of the alae orbitales, is at first a very thin layer, but deepens relatively quickly, as may be seen in studying the development of the nasal fossae (p. 85).



Fig. i71. — Cartilaginous Basis Cranii of Embryo of 35 Mm.

A, the visceral, and B, the paraxial, portions of the cartilaginous alisphenoidal projection.


The mesoderm (below the fore-brain) which makes the fronto-nasal process is directly continuous with that round the hypophysial region, so that when this fronto-nasal mesoderm thickens, its condensation and subsequent chondrification is continuous with the presphenoidal cartilage The median continuation forward of the basal cartilage made m this way is the cartilaginous skeleton of the nasal septum , and the nasal fossae grow upwards and backwards beside this. When they reach the limit of their extension, their upper parts are immediately in front of, and flush with, the roots of the orbito-sphenoidal processes. The front portion of the chondro-cranium is now formed by the completion of the upper part of the nasal capsule, its fusion with the presphenoidal region behind, and with the orbital process posterolaterally through the medium of a broad spheno-ethmoidal plate of cartilage.

About the same time the visceral ala temporalis comes into position in front of the otic capsule. Its inner part is cartilaginous, and is attached to the post-sphenoid; its greater part is membranous.

The chondro-cranium, made up in this way, is well formed in the third month, presenting the appearance shown in Fig. 171.

Parts of the Chondro-cranium and their Ultimate Fate.

The parachordal basal cartilage lies between the two otic capsules, by subsequent ossification giving rise to the basi-occipital. It extends dorso-laterally, giving origin to the exoccipital and supra-occipital', the last is in two parts or halves, which pass round the neural axis and meet on its dorsal side, making that part of the occipital which is below the protuberance and upper nuchal lines. The hypoglossal nerve passes through the cartilage where the exoccipital extension arises.

The otic capsule is on each side, beside the basal plate. Nerves and vessels pass between it and the plate, but it establishes continuity with it round these structures. Its antero-medial extremity becomes fused with the basisphenoidal cartilage directly, and, farther out, more indirectly through the medium of a temporary commissure (alicochlear commissure), which connects it with a short alisphenoidal extension from the basisphenoidal region; this encloses a foramen through which the carotid artery passes. The greater part of this cartilaginous otic capsule forms the petro-mastoid.

In the central or sphenoidal region of the basal cartilage, although the plate is continuous throughout, it is nevertheless convenient to distinguish a basisphenoidal and a presphenoidal part. The former shows a ridge, the dorsum sellce. The hypophysial fossa is in front of this, with middle clinoid prominences on each side of it, and the alisphenoidal projection already mentioned is continuous with the side of this part of the sphenoidal region (B, Fig. 171). The presphenoid shows the orbito-sphenoidal processes projecting from its upper lateral aspects, pierced at their bases by the optic foramina. These are curved plates of cartilage, supporting the cerebral vesicles, and continuous in front with the outer walls of the nasal capsule by means of the spheno-ethmoidal plate; this plate is a further chondrification of the paraxial mesoderm underlying the cerebral vesicles (Fig. 170) with which the mesodermal walls of the nasal capsule are continuous. When ossification occurs, the frontal bone is formed in membrane below the spheno-ethmoidal plate, the inner part of the orbito-sphenoid is ossified, and the remaining part, with the plate, disappears.



There is a cartilaginous backward prolongation from the outer end of the orbito-sphenoid, variable in extent. It is not shown in the figure, but its position is indicated on the left side by interrupted lines. It seems to be the remnant of a ‘ parietal plate ’ of cartilage connecting the orbito-sphenoid with a broad parietal plate which is attached (Fig. 169) to the outer part of the otic capsule, but which, being at a higher level than the plane of section in the drawing, is not shown in Fig. 171. This incomplete backward extension makes the outer boundary of a triangular interval behind the orbitosphenoid, in which the cartilaginous rudiments of the greater wing of the sphenoid are seen. These rudiments consist, on each side, of two cartilaginous structures, distinct in their origins: {a) An inner paraxial portion extending out from the basisphenoidal cartilage, and affording the commissure with the otic capsule; this part becomes the lingula ; (b) a larger outer portion, at a lower level, derived from visceral (maxillary) mesoderm, and secondarily attached to the first part; this makes the inner part of the greater wing and the root of the lateral pterygoid plate.

The pterygoid hamulus of the inner plate is preformed in cartilage.

Meckel’s cartilage and Reichert’s bar, of visceral origin, form part of the chondro-cranium. The first has its ventral end involved in the ossification of the mandible, its dorsal end forms the malleus and incus, while the remaining or intermediate part disappears. Reichert’s cartilage, having separated off the stapedial rudiment from its dorsal end, becomes attached to the otic capsule, where it forms the tympanohyal ; it makes the styloid process below this, and the stylo-hyoid ligament and small cornu of the hyoid bone at a lower level.

The cartilaginous olfactory capsule is open below and above, but the upper opening is partly bridged across, at a later date, round the fibres of the olfactory nerves. It consists of a median septum and two lateral walls. The cartilaginous septum is continuous above and behind with the presphenoidal cartilage. Its upper and back part ossifies as the perpendicular plate of the ethmoid, the remainder forming the main septal cartilage. Each lateral sheet forms the orbital plate in its upper part, remaining cartilaginous below this until it disappears; the lower and front portion of this sheet constitutes the basal part of the inferior nasal concha in its anterior part. The other nasal conchge and sinus walls are formed as secondary structures on the inner aspect of the lateral plate. The upper and back extremity of the capsule is in the form of a cup-like recess, and the sphenoidal concha is developed from this.

The upper surface of the brain is covered by mesoderm in which bones are developed in membrane. Certain broken bands of cartilage, however, are found running across this region in its posterior part, just above the supra-occipital region. These are known as ‘ tecta,’ and may be remnants of a more extensive cartilaginous cranium.

They are covered by the membrane bones, and disappear early in foetal life.


3. Osseous Stage.—The general formation of bones corresponding with the cartilage has just been described, and the details of ossification are given under the individual bones.

B. Facial Skeleton

With the exception of Meckel's cartilage, which has already been described, the skeleton of the face is not preformed in cartilage, although it is in many places applied to the cartilaginous substratum of the chondro-cranium.

The frontal bone has been seen already to be formed in membrane on the orbital surface of the spheno-ethmoidal plate, its facial portion extending upward in front of the margin of this plate.

The lacrimal and nasal bones, and probably also the frontal process of the maxilla, are formed in the mesoderm covering the anterior and upper, unossified, parts of the nasal capsule. The frontal process of the maxilla appears to incorporate with it in its growth a small projection of cartilage, the ‘ paranasal process,’ jutting out from the wall of the nasal capsule.

The bones below the level of the eyes are formed in the mesoderm of the maxillary process. This process, growing forward below the eye on each side, reaches the lower edge of the outer wall of the nasal cavity, and passes inwards below this to reach, fuse with, and invade the fronto-nasal process. The part below the eye gives origin to the body of the maxilla, while that part which covers in, by its invasion, the fronto-nasal process is the seat of development of the premaxillary portion of the jaw. The mesodermal mass, however, is thickest behind the region of the maxilla, extending, in this broad part of the face, from skin to wall of pharynx, or common mouth cavity of the younger embryonic stages; the outer and greater portion of this mass is used in forming certain soft parts, but a membrane bone, the medial pterygoid plate, is developed in its inner part, and the lateral plate is completed more superficially.

In front of the pterygoid region the maxillary mass makes the side wall of the common mouth cavity, and also covers a great part of the roof of this cavity, reaching, in both situations, the margins of the posterior bony apertures of the nose. It extends along the inner aspect of the outer nasal wall, and on the surface of the septum, and, on the side wall of the mouth, forms the palatine fold, which closes in the greater part of the posterior opening. The palatine bone is formed in this mesoderm lining the inner aspect of the outer wall of the nasal capsule, and extends into the palatine fold, the palatine shelf of the maxilla growing into the fold in front of it. The vomer is developed in the corresponding layer covering the lower and posterior portion of the nasal septum, that part which is not used in the formation of the perpendicular plate of the ethmoid.

The zygomatic forms in an upgrowth of maxillary mesoderm behind the eye. This upgrowth of visceral mesoderm is associated with the growth of the temporal muscle and other structures, and it is probable that the squamous portion of the temporal and zygomatic process are really visceral bones formed in this mesoderm and applied to the cartilaginous remnants already described as forming the parietal plate. The tympanic bone is developed in membrane of visceral origin.


Summary of Classification of Skull Bones.


Cartilage

bones


Cranium

<

Membrane

bones


Paraxial.

Occipital, petromastoid, body and orbital process of sphenoid with lingula, ethmoid.

Interparietal, parietal, frontal.


Face


, Cartilage

bones


Membrane Nasal, lacrimal. bones



The Hyoid Bone.


Visceral.

Inner small part of alisphenoid, ossicles of ear, hamular end of medial pterygoid plate.

Outer part of alisphenoid, pterygoid processes, tympanic ring and squama.

Small part of frontal process of maxilla (Meckel’s rod in lower jaw).

Maxilla, zygomatic, palatine, vomer, mandible, posterior part of inferior nasal concha (?).


The hyoid bone forms a part of the visceral-arch skeleton of the skull, and the structures concerned in its development are the second and third visceral arches of each side.

Second Visceral or Hyoid Arch. —The cartilage of this arch is known as the hyoid bar, or cartilage of Reichert, and its distal or ventral segment gives rise to

the lesser horn or cerato-hyal.

Third Visceral or Thyro-hyoid Arch. —The distal or ventral end of the cartilage

of this arch is connected with that of its fellow of the opposite side by a median piece of cartilage, which acts as a bond of union between them, and is from that circumstance called the copula. The copula also connects the right and left hyoid bars. The body of the hyoid bone, or the basi-hyal, is developed from, the copula; and each greater horn, or thyro-hyal, is developed from the cartilaginous bar of the corresponding third visceral arch.


The Teeth

The teeth are divided into two sets—namely, the temporary, milk, or deciduous, which belong to early infancy, and the permanent, which replace the temporary. The temporary teeth are twenty in number--ten upper, five in each maxilla, and ten lower, five in each halt ot the mandible. The number of permanent teeth is thirty-two—sixteen upper, and sixteen lower.

The Permanent Teeth.—Proceeding from the median line in a irection outwards and backwards, the permanent teeth are as follows: mec lal incisor, lateral incisor, canine, first premolar, second premolar, and first, second, and third molars. The third molar is known as the dens serotinus or wisdom tooth. Each tooth is composed of the following parts: the crown, which is the part above the gum; the root, which is the part embedded in the socket; and the neck, which lies between the crown and root. The surface of a tooth which looks towards the lip is called labial, and that looking towards the tongue lingual, whilst the opposed surface of one is called medial or proximal, and the other lateral or distal.

The Incisors.—There are eight incisor teeth—two in each upper jaw, and two in each half of the lower jaw. In each case the two incisors are known as medial and lateral respectively. Their crowns are chisel-shaped, the anterior surface being convex and the posterior concave.

The upper medial incisor is larger than the lateral, and it gradually tapers from the cutting edge of the crown to the root. The length of the crown exceeds its breadth. The labial surface is slightly convex, whilst the lingual surface is concave. The lingual surface presents near the gum a ridge, called the cingulum. The medial angle of the cutting edge of the crown is longer or more projecting than the lateral angle.

The root is long, tapering, and conical.

The upper lateral incisor is smaller than the medial, which it for the most part resembles. The lateral angle of the cutting edge of the crown is rounded off, and the cingulum is more prominent than in the upper medial incisor.

The lower medial incisor is smaller than the lateral, and narrower than the upper medial incisor. The cingulum, if present, is not well marked. The root is much compressed laterally.

The lower lateral incisor is larger than the medial, which it for the most part resembles. The presence of a cingulum is rare. The root is longer than that of the medial incisor, and on each flattened lateral surface there may be an indication of a longitudinal groove.




Fig. 172. — The Permanent Teeth of the Left Side.




The Canines. — There are four canine teeth—one in each upper jaw, and one in each half of the lower jaw.

The crown of a canine tooth is larger than that of an incisor. It is somewhat conical, and terminates in a cusp, from which circumstance the canine teeth are known as the cuspidate teeth. The labial surface of the crown is convex, and the tip of the cusp is nearer the anterior or medial than the posterior or lateral margin of the crown.

In the upper canines the lingual surface of the crown usually presents a slight median ridge, which extends from the cusp to a ridge which represents the cingulum. The root is long, thick, and almost round.

The lower canines have no median ridge on the lingual surface, which may be slightly concave. The cingulum is absent. The root is shorter than in the upper canines.

The Premolars. — There are eight bicuspid teeth—two in each upper jaw, and two in each half of the lower jaw.

Upper Premolars. — The crown is cuboidal, and its labial border is longer than the lingual. It has two cusps—labial and lingual—both of which are prominent. The labial cusp is the larger and broader of the two, and the cusps are separated by a deep fissure. The labial and lingual surfaces of the crown are convex, and there is no cingulum. The root is single, much compressed laterally, and usually marked on either side by a longitudinal groove.

The first upper premolar has frequently two slender roots. This occurs so often that it may be regarded as the normal condition in that tooth.

The second upper premolar differs from the first in the following respects: (i) Its crown is larger, and approaches more nearly the molar type; and (2) its lingual cusp is larger and broader than that of the first upper premolar, so that its labial and lingual cusps are of nearly equal size.

Lower Premolars.—These teeth are smaller than the upper premolars. The labial cusp has an inclination inwards towards the mouth, and the lingual cusp is depressed. The cusps are connected by a low-lying ridge. The root is single, round, and tapering.

The second lower premolar differs from the first in the following respects: (1) Its crown is larger, and approaches more nearly the molar type; and (2) its lingual cusp is stout, and not so much depressed as that of the first lower bicuspid.

The second lower premolar has occasionally two roots.

. Molars ( Multicuspidate Teeth). —There are twelve molar, or grinding teeth three in each upper jaw, and three in each half of the lower jaw.

First and Second Upper Molars.—The upper surface of the crown

is somewhat square, the angles being rounded off. The grinding surface is furnished with four cusps, situated at each angle of the quare, two of them being labial and two lingual. The anterior lingual usp is the largest, and it is connected with the posterior labial cusp y a stout oblique ridge. The labial cusps are longer or more projectlg than the lingual cusps, which applies to all the upper molars, 'he fissure between the two labial cusps and that between the two ngual cusps appears for a short distance on the labial and lingual urfaces of the crown respectively. The posterior lingual cusp is ccasionally suppressed.

It is usually fairly easy to place an upper molar in position by oticing the roots; these are recurved at their ends, so that the front f the tooth is easily told. Of the three roots, two are labial and one ngual.

In the lower molars the roots are also recurved, but to decide diich is the labial and which the lingual side the crown must be arefully noticed, remembering that the upper teeth overlap the lower Lterally. On account of this the outer or labial edge of the crown of he lower tooth is worn, while in the upper tooth it is the inner edge diich is slightly bevelled by wear.

Third Upper Molar. — This tooth is subject to much variety. Its rown is usually of smaller size than that of the first and second, 'he two lingual cusps of the crown are frequently confluent. The tiree roots are blended together to form a tapering cone.

Lower Molars. — The first lower molar is the largest. The upper urface of the crown is somewhat square, and its grinding surface is rovided with five cusps. Four of these are placed at the angles of he square, and are separated from each other by a crucial fissure, 'he posterior limb of this fissure bifurcates, and the fifth cusp lies in he angle of bifurcation. This cusp may be in the middle line, but usually lies towards the labial aspect, from which aspect it can sadily be seen. The lingual cusps are longer or more projecting han the labial cusps, which applies to all the lower molars. The ssure which separates the two labial cusps usually passes for a short istance on to the labial surface of the crown, but the fissure between ie two lingual cusps only occasionally passes on to the lingual surface f the crown. The root has two fangs— anterior and posterior. Each mg is much compressed from before backwards, and in most cases ach presents a slight backward curve.


The second lower molar bears a general resemblance to the first, 'he fifth cusp is often absent, and, when present, it is of small size, 'he two fangs of the root are frequently blended together.

The third lower molar is of larger size than the third upper molar, ts crown is large, and is usually provided with five cusps. Its root lay have two separate fangs, or these may be confluent. In the itter case a groove indicates the double condition of the root.

Dental Arches.—The alveolar arches of the maxillae and mandible, nd the upper and lower teeth, are so disposed as to form two almost imilar curves. When the mouth is closed, the summits of the crowns of the upper and lower teeth are brought together, the line of contact being known as the dental articulation.

Since the upper median incisor has a much wider crown than the lower its outer edge overlaps the lateral lower incisor crown, and this overlap is maintained throughout the dental arcade, the interval between two upper teeth corresponding to the crown of a lower. The two arcades end posteriorly in the same vertical line owing to the third upper molar being smaller than the lower.

The Temporary Teeth.—Proceeding from the median line, these are as follows on either side: two incisors, central and lateral, one canine, and two molars, first and second. Their necks are more constricted than in the permanent set. The incisors and canines resemble, for the most part, those of the permanent set, but they are smaller. The molars, which are replaced by the permanent premolars, exceed them in size, the second molars being particularly


Fjg. 173. — The Maxilla and Mandible at the Seventh Year, showing Most of the Temporary Teeth, and the Permanent Teeth about

TO REPLACE THEM.


The first permanent molars and the permanent lower central incisors

are in position.


large. The first upper molar has three cusps—two labial and one lingual; the second upper and first lower molars have each four, and the second lower molar has five.

In addition to these distinctions, the milk teeth are whiter than the permanent ones, and the roots of the molars more widely splayed. Moreover, their crowns are more bulbous.

Eruption of the Teeth.—The eruption of particular teeth of the lower jaw precedes that of the corresponding teeth of the upper jaw, and the somewhat variable times of eruption may be taken, for practical purposes, to be as follows:


Incisors . . First molars Canines . . Second molars


Temporary Teeth.

6th to 12th month. 12th to 14th ,, 14th to 20th 20th to 24th ,,


Permanent Teeth.


First molars

9 6th year.

Central incisors

7th „

Lateral incisors

8th ,,

First premolars

, ,

9th „

Second premolars

• •

10th ,,

Canines

4 #

nth ,,

Second molars

12th ,,

Third molars

• •

17th to 25th year.

About the sixth year is the period at which most teeth a


the jaws, there being the twenty temporary teeth, and all the peranent, except the four wisdom teeth (namely, twenty-eight), making all forty-eight.


Fig. 174. — Sections of Teeth. A, lower molar; B, lower incisor.


Structure of a Tooth.—The crown of a tooth contains a central ivity, called the pulp cavity, which is occupied by the dental pulp, he shape of the pulp cavity corresponds with that of the crown, and extends into the root, and as many fangs as compose it, terminating l a small opening on the apex of the fang. The cavity also extends >r a little into the cusps of the premolars and molars, and in the insors it is continued into each angle of the crown. The wall of the ivity presents a number of openings, which lead into the dental maliculi. The dental pulp is composed of a matrix of connective ssue, containing bloodvessels, nerves, cells, and fibres, which latter lem to be processes of the cells. It is destitute of lymphatics. The dls are scattered throughout the matrix, and at the surface of the pulp they form a continuous layer, being there known as the odontoblasts. This layer is sometimes spoken of as the membrana eboris. The pulp is very vascular and sensitive, its vessels and nerves reaching it through the minute openings at the apices of the roots.

The substance of the tooth is formed of three tissues—namely, ivory or dentine, enamel, and cement or crusta petrosa. The dentine forms the principal part of the tooth, surrounding the pulp cavity and its prolongations; the enamel covers the exposed part or crown; and the cement covers the root.


Fig. 174A. — Section of the Root of a Tooth.

1, cement; 2, granular layer of Purkinje; 3, dental canaliculi.


Fig. 174B. — Enamel Prisms.

A, four prisms (longitudinal view); B, surface of the enamel.


Dentine.—This bears a resemblance to bone, but contains rather less animal and more earthy matter, the proportion in 100 parts being about 28 of animal matter to 72 of earthy. The dentine has a striated appearance, due to the fact that it is traversed by a number of minute branched channels, called the dental canaliculi, which radiate in a curved manner outwards from the pulp cavity to the deep aspect of the enamel and cement. These tubules contain processes of the odontoblasts which form the membrana eboris, and are known as Tomes’ fibres. The part of the dentine adjacent to the enamel and cement is known as the granular layer of Purkinje. It presents a number of irregular spaces, known as the interglobular spaces, which e surrounded by minute globules of calcareous matter.


Enamel. — This caps and protects the dentine of the crown. It exceedingly hard, which is due to the fact that it contains no animal atter—at least, to any appreciable extent. It consists of solid ixagonal prisms, which are marked by transverse striations. These e received by their deep extremities into depressions on the dentine, id are placed vertically on the summit of the crown, but horizontally 1 its sides. At the period of eruption of a tooth, and for some little ue thereafter, the enamel of the crown is covered by a thin membrane, lied the enamel cuticle, or Nasmyth’s membrane.


Fig. 175. — Diagrams to show Formation of Enamel Organs.


The primary dental lamina ( p.dl) is divided by a mesodermal upgrowth into dental ( dl) and labio-dental (Id) laminae. Enamel organ forms the labial side of shelf, that of the permanent tooth (perm) from its free border. gub., gubernaculum, a remnant of the lamina; l-ds, labio-dental sulcus; ee, external epithelium; st, stellate reticulum; am, ameloblast layer.

Cement, or Crusta Petrosa.—This covers the dentine which forms le root of the tooth. It is true bone, and contains lacunae and canalici, but it is destitute of Haversian canals.

The root of a tooth is maintained in its socket by the dental peristeum (periodontal membrane), which covers the cement, and lines the all of the socket, being continuous with the gum at the neck of the >oth. The articulation is called gomphosis.

Development of the Teeth.

The teeth are calcified papillae of the gingival mesoderm, their crowns being >vered by calcified ectodermic cells. Three structures are involved in the welopment of a tooth—namely, (1) the enamel organ, which furnishes the iamel\ (2) the dental papilla, which gives rise to the dentine and dental pulp; id (3) the dental sac, from the inner layer of which the cement is formed. The lamel organ is developed from the ectoderm, whilst the dental papilla and the mtal sac are of mesodermic origin.


The development of the temporary teeth begins by a thickening of th covering epithelium, which is gradually depressed below the general surface This is usually described as ‘ ingrowth of the epithelium,' but what actualh occurs is that the mesoderm, first on its lingual side and then in front of it, grow; up beside the line of thickening, which retains its original level. In this wai a sunken ridge of epithelium forms in each jaw, like a reversed projection fron the surface, with its ‘ free ’ edge directed into the mesodermal bed. This i known as the primary dental lamina. The later growth of mesoderm, on it: outer or labial face, leads to the buried ridge in its further deepening bein£ subdivided from below, as it were, and thus (Fig. 175) showing now an anterioi labio-dental lamina and a posterior dental lamina. The labio-dental or labiogingival lamina is concerned with the lip and gum, and it presents superficially a furrow, called the labio-dental or labio-gingival groove , which divides it into twc parallel ridges —labial for the lip, and gingival for the gum. The labio-gingiva groove itself deepens, and separates the lip from the gum.



Fig. 176. Dfvelopment of Tooth (Frey, after Thiersch) : Vertical Transverse Section of Upper Jaw.


Ihe true dental lamina is concerned with the enamel. Along its attach ment to the oral epithelium a furrow is formed, called the dental furrow, an. 1 s v^P m argm lies in the mesoderm of the embryonic jaw.

e ^ rue dental laminae, which are of ectodermic origin, are at first up soon become broken up into separate masses, called enam( organs, there being twenty of these for the temporary teeth, ten upper an

ch e ™ m * 1 or ^ an appears as a thickening or protuberance c anr ° p d ™ lc £ ells 011 tbe deep margin of the true dental lamina, which protubei neck flask-shaped the neck being directed superficially. Thi

the ectnH 5rmi n u tbe connection between the enamel organ am

strand o?eeU + L S K f the ^ ree surface of the gum is thereby maintained by ; from one aunfh e gabe ^uaculum. Moreover, the enamel organs become isolatei lamina 116 th by the brea kmg down of the interposed cell-layers of th

each^enanfel^nrcr^ a PP ear f as an elevation of the mesoderm subjacent t< of enamel ore-af« a ^ en n ^ mber papillae, therefore, corresponds to the numbei b • • s the dental papilla grows, it becomes capped by the ename'


-cran, which also invests it laterally. The enamel organ thus becomes moulded Jer the dental papilla in the form of a cap.

Enamel Organ. —As stated, the enamel organ is of ectodermic origin, being drived from the true dental lamina, which, in turn, is derived from the ectosrmic cells covering the surface of the gum. The chief cells of the enamel -gan are situated deeply, and lie close to the surface of the dental papilla, hey are long columnar cells, which are called enamel cells, adamantoblasts,

ameloblasts, and they give rise to the enamel prisms. Formation of Enamel Prisms. —Each enamel cell gives rise to one enamel nsm. The deep part of each cell undergoes calcification. The superficial ids of the enamel cells do not become calcified, but form a delicate membrane, died the enamel cuticle, or Nasmyth’s membrane, which covers the crown of ie tooth for a short time after its eruption.

Dental Papilla. —As stated, the dental papilla is of mesodermic origin, and gives rise to the dentine and dental pulp. Essentially, the papilla is a collecon of mesodermic cells, which become transformed into connective tissue, lis being permeated by bloodvessels and nerves.

The cells at the surface of the papilla become enlarged, and are called odontoasts. These cells are identical with the osteoblasts of developing bone, and ley form a continuous layer, known as the membrana eboris. From these ills the dentine is laid down. The central portion of the dental papilla, consting of connective tissue, bloodvessels, and nerves, constitutes the dental lip.

Hertwig’S sheath is a prolongation of ectodermal cells from the periphery

the enamel organ, surrounding the growing dental papilla. It appears to be icessary for the formation of dentine in the papilla, for this substance does not >rm in the absence of ectoderm.

Formation of Dentine. —The dentine is laid down in successive layers. Each yer consists at first of a fibrous dentinal matrix, called prodentine, the fibres

which are continuous with those of the dental pulp. Subsequently the atrix undergoes calcification by the deposits of calcareous matter. During ie formation of these layers the odontoblasts become shifted inwards towards ie centre, and they leave behind them fine processes, which become invested y the calcified fibrous matrix of the dentine. In this manner the dental canalicli are formed, with processes of the odontoblasts within them, which represent ie fibres of Tomes. The dentine so formed constructs a case for each dental ipilla. The central part of the papilla, consisting of connective tissue, bloodessels, and nerves, forms, as stated, the dental pulp. The peripheral part of le dentine has several small uncalcified areas, which lie between globular Lasses of calcareous matter. These areas represent the interglobular spaces of ie adult tooth.

Dental Sac.— This sac, like the dental papilla, is of mesodermic origin. As ie dental papilla is undergoing differentiation into dentine and dental pulp, ie mesodermic connective tissue around the papilla becomes condensed into follicle, called the dental sac, which encloses both the dental papilla and the ^responding enamel organ. The developing tooth (enamel organ and dental apilla) thus becomes isolated, the enamel organ being only in connection with ie ectoderm of the gum by its neck. The part of the dental sac which is related ) the crown of the tooth is connected with the surface of the gum by a band E connective tissue. This part of the sac disappears. The part of it which is dated to the root of the tooth undergoes important developments. It consists E two layers—inner and outer. The inner layer gives rise to the cement, or

usta petrosa, which breaks up the sheath of Hertwig as it forms, whilst the outer yer, remaining fibrous, forms the dental periosteum, or periodontal membrane.

Permanent Teeth. —The process of development of the permanent teeth is milar to that of the temporary teeth. The enamel organs of those permanent

eth ( teeth of succession) which are to replace the temporary teeth—namely, Le permanent incisors, canines, and premolars—are developed as thickenings

protuberances of the true dental laminae, as in the case of the temporary teeth, and they grow inwards on the lingual aspects of the temporary enamel organs (see Fig' 175).

The enamel organs of the three permanent molar teeth spring from a backward prolongation of the true dental lamina.

Teeth Present at Birth. —At the period of birth the gums contain forty-four teeth. These consist of—(1) the twenty temporary teeth; (2) the twenty permanent teeth, which are to replace the temporary teeth; and (3) the four first permanent molar teeth. At birth the second and third permanent molar teeth, eight in all, are not yet developed.

Eruption of the Temporary Teeth. —As the permanent teeth grow, they exercise pressure upon the roots of those temporary teeth which they are about to replace. This continued pressure leads to partial absorption of the roots of the temporary teeth. These teeth, therefore, become loosened in their sockets, and as the permanent teeth continue to advance, the loosened temporary teeth are pushed out by the advancing permanent teeth. Osteoclasts also take part in the absorption of the roots. The actual forces at work to bring about eruption are quite unknown.