Talk:Book - A Laboratory Manual and Text-book of Embryology 13

THE PERIPHERAL NERVOUS SYSTEM

The nerves, ganglia, and sense organs constitute the peripheral nervous system. The peripheral nerves consist of bundles of myelinated and unmyelinated nerve fibers and aggregations of nerve cells, the ganglia. The fibers are of two types: afferent JiberSy which carry sensory impulses to the central nervous system, and afferent fibers, which carry effective impulses away from the nervous centers. The peripheral efferent fibers of both brain and spinal cord take their origin from neuroblasts of the basal plate. Typically they emerge ventro-laterally from the neural tube. Those arising from the spinal cord take origin in the mantle layer, converge, and form the ventral roots of the spinal nerves. The efferent fibers of the brain take origin from more definite nuclei and constitute the motor or effector portions of the cerebral nerves. The peripheral afferent fibers originate from nerve cells which lie outside the neural tube. Those sensory nerve cells related to the spinal cord and to the brain stem caudal to the Otic vesicle are derived from the ganglion crest, the origin of which has been described (Chapter X, p. 304).

A. SPINAL NERVES

The spinal nerves are segmentally arranged and each consists of dorsal and ventral roots, spinal ganglion, and nerve trunks. In embryos of 4 mm. the ventral roots are already developing as outgrowths of neuroblasts in the mantle layer of the spinal cord (Fig. 357). The spinal ganglia are represented as enlargements along the ganglion crest and are connected by cellular bridges.

In 7 mm. embryos (five weeks old) the cells of the spinal ganglia begin to develop centrally directed processes which enter the marginal zone of the cord as the dorsal root fibers (Fig. 358). These fibers course in the dorsal funiculi and eventually form the greater part of them. Perpihcral processes of the ganglion cells join the ventral root fibers in the trunk of the nerve (Fig. 360). At ]0 mm. , (Fig. 359) the dorsal root fibers have elongated an ramus communicans to the sympathetic ganglioii nj ventral (anterior) terminal rami. The efferent muscles of the lateral and ventral body wall, and integument of the same regions.

Fig. 357. — Reconstruction of an embryo of 4 mm., showing the development of the cerebrospinal nerves (Streeter). X 17. C/., 2., etc., cervical spinal nerves.

At the points where the anterior and lateral terminal rami arise, connecting loops may extend from one spinal nerve to another. Thus in the cervical region superficial and deep nerve plexuses are formed. The deep cervical plexus forms the ansa hypoglossi and the phrenic nerve (Fig. 359).

Fig. 359. — Recoastniction of the

The Brachial and Lumbosacral Plexuses. — The nerves supplying the arm and leg also unite to form plexuses. In embryos of 10 mm. (Fig. 359) the trunks of the last four cervical nerves and of the,first thoracic are united to form a flattened plate, the anlage of the brachial plexus. From this plate nervous cords extend into the intermuscular spaces and end in the premuscle masses. The developing skeleton of the shoulder splits the brachial plexus into dorsal and ventral lamirite. From the dorsal lamina arise the musculocutaneous, median, and 1 ulna nerv-fs; from the ventral lamina, the axillary and radial nerves.

In 10 mm. embryos the lumbar and sacral nerves which supply the leg unite 1 in a plate-like structure, the anlage of the lumbosacral plexus (Fig. 359). The J plate is divided by the skeletal elements of the pelvis and femur into two latera and two mL-rlian trunks. Of the cranial pair the lateral becomes the femor<d nerve; tht- median, the obturator nerve. The caudal pair constitute the sciatic nerve; the lateral trunk is the peroneal nerve, and the median trunk is the tibial.

Fig. 360.— Transverse sect!

Sympathetit: ganglian I. embryo showing the spinal e mi components. Diagmmmalii

Save for the neurones from the special sense organs fnnsc, eye. and ear) whichi.V form a special sensory group, the neurones of the peripheral nerves, both spinal and cerebral, fall into four functional groups (Fig. 360).

(1) Somatic ajferent, or general sensory, with fibers ending in the integumer of the body wall.

(2) Visceral ajferent or sensory, with fibers ending in the walls of the visct

(3) Somatic efferent or motor, with fibers ending on voluntary muscle fibers

(4) Visceral efferent or motor: (a) with fibers ending about sj-mpathetio ganglion cells, which in turn control the smooth muscle fibers of the viscera a blood vessels (spinal nerves); or (b) with fibers ending directly on visceral muscl fibers (mixed cerebral nerves).

B. THE CEREBRAL NERVES

The cerebral nerves of the human brain are twelve in number. They differ from the spinal nerves: (1) in that they are not segmentally arranged, and (2) in that they do not all contain the same types of nervous components. Classed according to the functions of their neurones they fall into three groups:

Sfecul Somatic Siksoky.

Somatic Motoi ob Efteuht.

VIBCEUL Sehsoit AND UtmW,

r. OUactory.

III. Oculomotor.

V. Trigeminal.

II. Optic.

IV. Trochlear.

VII. Facial.

VIU. Acoustic.

VI. Abducens.

++++XII. Hypoglossal.

X. Vagus complei, including XI. Spinal Accessory.

It will be seen (1) that the nerves of the first group are purely sensory, corresponding to the general somatic afferent neurones of the spinal nerves; (2) that the nerves of the somatic motor group are purely motor and correspond to the somatic efferent or motor neurones of the spinal nerves; (3) that the nerves of the third group are of mixed function and correspond to the visceral components of the spinal nerves.

L The Special Somatic Sensory Nekves I. The Olfactory Nerve, though purely sensory, has no ganglion. Its nerve

cells lie at first in the olfactory epithelium of the nose and are of the bipolar type

(fourth week). From these cells pjeriph++++eral processes develop and end directly

at the surface of the olfactory epithelium {Fig. 361). Central processes grow

toward the olfactory lobe and form the

strands of the olfactory nerve. They end

in the glomeruli of the olfactory bulb in

contact with the dendrites of the mitral

cells, or olfactory neurones of the second

order. Some olfactory cells migrate

from the epithelium, with which, however, they retain peripheral connections.

Such bipolar cells, found along the entire course of the nerve, resemble ordinary

dorsal ganglion cells. The olfactory nerve fibers are peculiar in that they remain

unmyelinated. Nerve fibers from the epithelium of the vestigial vomero-nasal

organ (of Jacobson) also end in the olfactory bulb.

When the ethmoidal bone of the cranium is developed, its cartilage, as the

cribriform plate, forms around the strands of the olfactory nerve.

FiC. 361.— Diagram of the relations al the fibers in the olfactory ner\'e.

The ganglionated n. terminalis courses in close assocktion with the olfactory nerve. Its fibers end in the epithelium of the vnmero-nasal organ and of the nose. Although evidently a distinct nerve its significance is obscure.

2. The Optic Herre is formed by 6bcrs which take their origin from neuroblasts in the nervous layer of the retina. The retina is differentiated from the wall of tile fore-brain and remains attached to it by the optic stalk (Fig. 343), hence the optic nerve is not a true peripheral nerve, but belongs to the central system of tracts. The neuroblasts from which the optic nerve fibers develop constitute the ganglion cell layer of the retina (Fig. 381). During the sixth and seventh weeks these cells give rise to central processes which form a furce fiber layer on the inner side of the retina. The optic fibers converge to the optic stalk and grow through its wall back to the brain. The cells of the optic stalk are converted into a neurogUa framework and the cavity is obliterated. In the floor of the fore-brain, at the boundary between telencephalon and diencephalon, the fibers from the median half of each retina at about the end of the second' month cross to the opposite side, and this decussation constitutes the optic cHasma (from Greek letter Jf or "chi"). The crossed and uncrossed fibers constitute the-; optic trad which rounds the cerebral peduncles laterally and dorsally (Fig. 354), Eventually the optic fibers end in the lateral geniculate body, thalamus, and superior colliculus.

Efferent fibers, terminating in the inner reticular layer of the retina, are also present. In certain fishes where their function has been studied these fibers resemble visceral efferent components (Arey, Jour. Comp. Neurol., vol. 26, 1916).

8. The Auditory Nerve, or N. Acusticus, is formed by fibers which grow from the cells of the acoustic ganglion. l"he origin of these cells is unknown, though they appear in 4 mm. embryos just cranial to the otic vesicle {Fig. 358). The cells become bipolar, central processes uniting the ganglion to the luberculum acusticuti! of the myelencephalon and peripheral fibers connecting it with the wall of the otocyst. The acoustic ganglion is differentiated into the vestibular and spiral ganglia (Fig. 362). Its development has been studied by Streeter (Amer. Jour. Anat., vol. 6, 1907). The ganglion elongates and is subdivided into superior and inferior portions in 7 mm. embryos. The superior part supplies nerves to the utriculus and to the ampulla of the anterior and lateral semicircular canals. It forms part of the vestibular ganglion of the adult. Part of the inferior portion supplies nerves to the sacculus and to the ampulla of the posterior semicircular canal, and this portion, together with the pars superior, constitutes the veslibtitar ganglion. The greater part of the pars inferior is, however, differentiated into the fibers form the cochlear division of the acoustic nerve. This is distinctly separated from the central fibers of the vestibular ganglion which constitute the vestibular division of the acoustic nerve, the fibers of which are not auditory in function. The pars inferior of the vestibular ganglion becomes closely connected with the n. cochJearis, and thus in the adult it appears as though the sacculus and posterior ampulla were supplied by the cochlear nerve, Spiral ganglion, the peripheral fibers of which innervate the hair cells of the spiral organ (of Corti) in the cochlea. The spiral ganglion appears in 9 mm. embryos and conforms to the spiral turns of the cochlea, hence its name. Its central nerve

THE CEREBRAL NERVES

Fic. 362. — The development of Uie acoust c ganglia and nerves The vestibular gangUon is finely stippled the sp lal ganglion coarsely stippled (Strecter)

n. The Somatic Motor Nerves

The nerves of ihis group, consisting of the three nerves to the eye muscles and the n. hypoglossus, are purely motor nerves, the fibers of which take origin | from the neuroblasts of the basal plate of the brain stem, near the midline. They i are regarded as the homologues of the ventral motor roots of the spinal cord, but I have lost their segmental arrangement and are otherwise modified. The nuclei I of origin of these nerves are shown in Fig. 364.

12. N. Hypoglossus. — This nerve is formed by the fusion of the ventral root I fibers of three to five precervical nerves. Its fibers take origin from neuroblasts ■ of the basal plale and emerge from the ventral wall of the myclencephaJon in several groups (Fig. 357). In embryos of live weeks (7 mm.) the fibers have converged venlrally to form the trunk of the nerve (Fig. 358). Later they grow cranially, lateral to the ganglion nodosum, and eventually end in the muscle fibers of the tongue fPig, 359), The nerve in its development unites with the first three cervical nerves to form the ansa hypoglossi. IXs nucleus of origin is shown in Fig. 364.

That thL- hypoglossal is a composile nerve homologous with the venlral roots of the ( spinal nerves is shown; (1) by the segmental origin of its fibers; (2) from the fact thai ii nucleus of origin is a cranial continuation of the ventral gray column, or nucleus of origin for

that in

++++(he ventral sjMtial roots; (3) from the fafi

rudimentary dorsal ganglia are

dorsal root lo the hypoglossal,

rudimenlary structure (Figs. 359 ai.>.

cervical nerve may also degenerate at

Neurol., vol. 20, I'oiO) has found two and . i.i.

which dorsal roots extended to the root fascicles o(

.alian embryos (pig, sheep, cat, etc.) al least (Froriep's ganglion) sends a. iriep's ganglion may be present as a absent and the ganglion of the first pig embryos Prentiss (Jour. Comp. y ganglia (including Froriep's) from, 1 ypoglossiil nerve (Fig, 121).

3. The Oculomotor Nerve originates from n^ ^ in t

the mesencephalon (Fig. 339 B). The fibers em( * small iaes

ventral surface of the mid-brain in the concavity du ceph lesure

359 and 364). The fascicles converge, form the tru ner\ id end ii

premuscle masses of the eye. The nerve eventua es i the extrindt muscles of the eye save the superior oblique and external rectus. A branch is also supplied to the ciliary ganglion. In the chick embryo, bipolar cells migrate along the fibers of the oculomotor nerve to take part in the development of the ganglion. The ciliary ganglion of human embryos is derived entirely from the semilunar ganglion of the trigeminal nerve.

4. The Trochlear Nerve fibers take their origin from neuroblasts of the basal plate, located just caudal to the nucleus of origin of the oculomotor nerve. They are directed dorsally, curve around the cerebral aqueduct, and, crossing in its roof, emerge at the isthmus (Fig. 339 A). From their superficial origin each is directed ventrally as a slender nerve which connects with the anlage of the superior oblique muscle of the eye (Fig. 359).

6. The N. Abducens takes origin from a nucleus of cells in the basal plate of the myelencephalon, located directly beneath the fourth neuromere of the floor of the fourth ventricle (Figs. 359 and 364). The converging fibers emerge ventrally at a point caudal to the future pons, and, as a single trunk, course cranially, mesial to the semilunar ganglion, finally ending in the anlage of the external rectus muscle of the eye. Vestigial rootlets of the abducens and hypoglossal nerve tend to fill in the gap between these two nerves, according to Bremer and Elze.

m. The Visceral Mixed Nerves

The nerves of this group, the trigeminal, facial, glossopharyngeal, and vagus complex (vagus plus the spinal accessory), are mixed in function. The trigeminal nerve, beside its visceral nerve components, contains also numerous somatic sensory neurones which supply the integument of the head and face.

5. The Trigeminal Nerve is largely sensory. Its semilunar ganglion is the largest of the whole nervous system and is a derivative of the ganglion crest, but very early is distinct from the other cerebral ganglia (Fig. 358). It arises laterally at the extreme cranial end of the hind-brain. Central processes from its cells form the large sensory root of the nerve which enters the wall of the hindbrain at the level of the pontine flexure (Fig. 359). These fibers fork and course cranially and caudally in the alar plate of the myelencephalon. The caudal fibers constitute the descending spinal tract of the trigeminal nerve, which extends as far caudad as the spinal cord (Fig. 364). The peripheral processes separate into three large divisions, the ophthalmic, maxillary, and mandibular rami, and supply the integument of the head and face and the epithelium of the mouth and tongue.

The motor fibers of the trigeminal nerve arise chiefly from a dorsal motor nucleus which lies opposite the point at which the sensory libers enter the brain ] wall (Fig. 364). In the embryo these fibers emerge as a separate motor root, course along the mesial side of the semilunar ganglion, and, as a distinct trunk, 1 supply the premuscle masses which later form the muscles of mastication, rrom 1 the chief motor nucleus, a line of cells extending cranially into the mesencephalon . constitutes a second source of origin for motor fibers. In the adult, the motor] fibers form a part of the mandibular division of the nerve.

The facial, glossopharyngeal, and vagus nerves are essentially visceral in func- ] tion. Their sensory fibers, chiefly of the visceral type, supply the sense organsJ

++++f ganglion (jugu/ur) Atcrssmy root saMjiw

x-^J

Ccng. nodos.-^ N. laryng. sup.

Fig. 3W, — Kecoiutruction o£ the cerebral n

o( an embryo of 10.2 mm. {Stieeter). X 16.7.

of the branchial arch™ «.nrf yii

respective nerves,

caudaljy as the sm , . . „

the same origin and col e in the myelencephalon, supply the adjacent integu-^

ment.

i originate in the ganglia of theif J of the myelencephalon, course ■ somatic sensory fibers, ha\'iDJ

In aquatic vertebrates, special somatic sensory fibers from the laler, e org,

facial, glossopharyngeal, and vagus nerves, and their goi an cells torr I of t

late, petrosal, and nodose ganglia. In human embryos ih jans of the il line i

sented by ectodermal thickenings or placodes which o^- emporarilj r these j

The nervous elements supplying these vestigial organs :ompletely ppeared.

7. The Facial Nerve is largely composed of efferent motor fibers which supply the facial muscles of expression. In 10 mm. embryos these fibers arise from a duster of neuroblasts in the basal plate of the myelencephalon located beneath the third rhombic groove or neuromere (Fig. 364). The fibers from these cells course laterally, and emerge just mesial to the acoustic ganglion. The motor trunk then courses caudally and is lost in the tissue of the hyoid visceral arch, tissue which later gives rise to the muscles of expression (Fig. 359) . The sensory fibers of the facial nerve arise from the cells of the geniculate ganglion, which are in turn derived from the ganglion crest (Streeter). This ganglion is present in 7 mm.

Fic. 364. — Recon si ruction of the nucin of origin and termination oF the cerebral n of 10 mm. The somatic motor nuclei are colored red (Streeter). ;

embryos (Fig. 358), located cranial to the acoustic ganglion. The centrally directed processes of the geniculate ganglion enter the alar plate and form part of the solitary tract. The peripheral fibers in part course with motor fibers in the chorda lympani, join the mandibular branch of the trigeminal nerve, and end in the sense organs of the tongue. Other sensory fibers form later the great sttperficial petrosal nerve, which extends to the spheno-palatine ganglion.

The motor fibers of the facialis at first course straight laterad passing cranial to the nucleus of the abducens. The nuclei of the two nerves later gradually shift their positions, that of the facial ncr\-c moving caudad and laterad, while the nucleus of the abducens shifts cephalad. As a result, the motor root <rf the facial nerve in the adult bends around the nucleus of the abducens producing the genu or knee, of the former. The two together produce the rounded eminence in the floor of thi' fourth ventricle known as tiief<u:ial colliculus.

9. The Glossopharyngeal Nerve takes its superficial origin just caudal to the otic vesicle (iMgs. 35S, 363 and 365). Its few motor fibers arise from neuroblasts in the basal plate beneath the fifth neuromeric groove. These neuroblasts form part of the nucleus ambiguus, a nucleus of origin which the glossophar\-ngeal shares with the vagus (Fig. 364). The motor fibers course laterally beneath the spinal tract of the trigeminal nerve and emerge to form the trunk of the nerve. These fibers later supply the muscles of the pharynx.

The sensorj- fibers of the glossopharyngeal nerve arise from two ganglia, a superior, or root ganglion, and a petrosal, or trunk ganglion (Figs. 359 and 365). These fibers constitute the greater part of the ner\'e and divide f>eripherally to form the tympanic and lingual rami to the second and third branchial arches. Centrally, these fibers enter the alar plate of the myelencephalon and Join the sensory fibers of the facial nerve coursing caudally in the solitary tract.

10, 11. The Vagus and Spinal Accessory.^The vagus, like the hypoglossal, is composite, representing the union of several nerves, which, in aquatic animals, supply the branchial arches (Figs. 359 and 365). The more caudal fascicles of motor fibers take their origin in the lateral gray column of the cervical cord as far back as the fourth cervical segment. These fibers emerge laterally, and. as the spinal accessory trunk (in anatomy a distinct nerve), course cephalad along the line of the neural crest (Figs. 358, 359 and 365). Other motor fibers take their origin from the neuroblasts of the nucleus ambiguus of the myelencephalon (Fig. 364). Still others arise from a dorsal motor nucleus which lies median in position. The fibers from these two sources emerge laterally as separate fascicles and join the fibers of the spinal accessory in the trunk of the vagus nerve. The accessory fibers soon leave the trunk of the vagus and are distributed laterally and caudally to the visceral premuscle masses which later form the stcmo<leido-mastoid and trapezius muscles of the shoulder (Fig, 359). Other motor fibers of the vagus supply muscle fibers of the pharynx and larynx.

As the vagus is a composite nerve it has several root ganglia which arise as enlargements along the course of the ganglion crest (Figs. 359 and 365). The more cranial of these ganglia is the ganglion jugiUare. The others, termed accessory gtuif^lia. are vestigial structures and not segmentally arranged. In addition to the root ganglia of the vagus the ganglion nodosum forms a ganglion . of the trunk (Fig. 365). The trunk ganglia of both the vagus and glossopharyngeal nerves are believed to be derivatives of the ganglion crest, their cells migrating ventrally in early stages.

The central processes from the neuroblasts of the vagus ganglia enter the wall of the myelencephalon, turn caudalward, and, with the sensory fibers of the

Vagus root gan^ion (Juiular)

IX. root gang. (Superior)

Sympatktlic Fig. 365. — A reconstructioD of Uk peripheral nerves in ui embiyo of 17.5 mm. (Streeter). X 16.7.

facial and glossopharyngeal nerves, complete the formation of the solitary tract. The peripheral processes of the ganglion cells form the greater part of the vagus trunks after the separation from it of the spinal accessory fibers.

The Segmentation of the Vertebrate Head.— The vertebrate head undoubtedly of fused segments. This was suggested to the earlier workers by the arrangement of the branchial arches (branchiomerism). and by the discovery, in the embryos of lower vertebrates, of so-called head carilies, homologous with mesodermal segments. (Note also the presence of neuromeres, p. 334.)

Assuming that the branchiomeres arc portions of the primary head segments — and there are recent observations which tend to disprove this— iheir segmentation is still not comparable to that of the trunk, for the branchial arches are formed by the segmentation of splaiiclmir mesoderm, tissue which in the trunk never segments. The branchial arches, therefore, represent a different son of metamerism.

Only the first three head cavities persist. These form the eye muscles, innervated by* the third, fourth, and sixth cranial nerves respectively. All the remaining muscles of the head are derivcif from the branchiomeres. From what has been said it is evident that one cannot compare the relation of the cranial nerves to the branchiomerie muscles with the relation of a spinal nerve to its myotomic muscles. For this reason the cranial nerves furnish unreliable evidence as to the primitive number of cephalic segments. Various investigators have set this number between eight and nineteen.

C THE SYMPATHETIC NERVOUS SYSTEM

The sympathetic nervous system is composed of a series of ganglia and peripheral nei-ves, the fibers of which supply gland cells and the smooth muscle fibers of the viscera and blood vessels. It may function independently of the central nervous system and is hence known as the aulonomic system.

The sympathetic ganglion cells are derived from the cells of tJie ganglion crest. In fishes discrete cellular masses become detached from the spinal ganglia. At an early stage (6 to 7 mm.) in human development, on the contrary, certain cells of the ganglion crest migrate ventrally and give rise to a scries of ganglia, which, in the region of the trunk, are segmentally arranged (Figs. 139 and 360). According to Kuntz (Jour. Comp. Neurol., vol. 20, 1910), the primary source of these errant cells is the neural tube, from which they migrate along both dorsal and ventral nerve roots. At 9 mm. the ganglionated cord is formed and fibers connecting the sympathetic ganglia with the spinal nerves constitute the r communicanles (Streeter). The more peripheral ganglia (cardiac and cceliac) and the sympathetic ganglia of the head may be found in 16 mm. embryos (Fig. 366).

The cells which are to form the ganglia of the sympathetic chain migrate ventrally in advance of the ventral root fibers and take up a position lateral to the aorta. These ganglionic anlages are at first distinct, but soon unite with each other from segment to segment, forming a longitudinal cord of cells. After the formation of the primitive rami communicantes by the root fibers from the spinal nerves, centripetal processes from tJie sympathetic cells grow back and join the trunks of the spina) nerves. The visceral, spinal fibers later become myelinated j and constitute the white rami; the sympathetic, centripetal fibers remain unmyeIinated and form separately the gray rami. Nerve fibers appear in the paired longitudinal cords, which were at first purely cellular, in such a manner that segmental masses of cells {sympathetic ganglia) become linked by fibrous, commissural cords.

In the head region the sympathetic gangUa are not segmentally arranged, but are derived from cells of the cerebrospinal ganglia which migrate to a ventral

Fig. 366. — The sympathetic system io a 16 mm. human embryo (Streeter In Lewis and Stfthr). X 7. The ganglkmated trunk is heavily shaded. The first and last cervical, thoracic, lumbar, sacraj and coccygeal spinal ganglia are numbered, a., Aorta; arc, accc<isoTy nerve; cor., carotid arter>'; cil., ciliary ganglion; coe., cocliac artery; Ht., heart; nod,, nodose ganglion; at., otic ganglion; prt., petrosal ganglion; s-m,, submaxHIary ganglioD; s.uks., superior mesenteric artery; »pk.-p., ^henopalatine ganglion; spl., splanchnic nerve; St., stomach.

position (Fig. 365). These cells likewise give rise to nerve fibers which constitute longitudinal commissures connecting the various ganglia of the head with the ganglionated cord of the trunk region. The small cranial sympathetic ganglia are probably all derived from the anlage of the semilunar ganglion (Fig. 366).

The ciliary ganglion is related by a ramus communicans to the ophthalmic diviaoO I of the trigeminal nerve and receives fibers from the oculomotor nerve. Its celb are probably derived entirely from the semilunar ganglion. The sphenopalatiMlM submaxillary, and otic ganglia probably take their origin from migrating cells of J the semilunar ganglion, but as they are connected with the geniculate ganglion the facial nerve, the latter may contribute to their formation. The sphenopal tine ganglion is connected directly with the semilunar ganglion by two 1 municatjng rami. The submaxillary ganglion is intimately related through thl mandibular division of the trigeminal nerve to the semilunar ganglion, while t otic ganglion is united to the latter by a plexus and is related to the glossopharyi gcal nerve through its tympanic branch.

The cerdcal ganglia lose their segmental arrangement and represent the fusion ' of from two to five ganglia of the cerWcal and upper thoracic region. The more distally located prevertebral ganglia (of the cardiac, cceliac. hjpogastric, and pelvic plexuses) are derived from cells of the neural crest which migrate to a greater distance ventrally (Fig. 366). The visceral ganglia (of the myenteric and submucous plexuses^ and the prevertebral cardiac plexus as well, are derived by Kunt2 chiefly from migratory cells from the hind-brain and from the vagus gangUa.

The sympathetic nerve cells give rise to axons and dendrites, and are thus t>'pically multipolar cells. Their axons possess a neurilemma sheath, but remain unmyelinated.

D. CHROMAFFIN BODIES! SUPRARENAL GLAND

Certain celts of the sympathetic ganglia Jo not form nerve cells, but are

transformed into peculiar gland cells whic

secretion formed by these cells causes the,

chrome salts, hence they are (

from the ganglionated cord of

as citromuffin bodies. Chrom '■•

mesenchimal tissue, form the 1

reaches a rclati\ely large size in hur 1

The Chromaffia Bodies of masses part!}- embedded in the dorsal si ce they may attain a diameter of 1 to 1.5 mm, several for each gan^on.

Similar chromaffin bodies niay ocoir in aU The largest of these structures found in the ab

duce an internal secretion. The to stain brown when treated with cells. Cells of this type deriv item give rise to structures knoi the cocliac plexus, together wil iprurenal gland, an organ whii '(Fig. 232).

ith

the aortic chromaffin bodies (of Zuckerkandl). These occur on either side of the inferior mesenteric artwy, ventral to the aorta and mesial to the metanephros. At birth they attain a length of 9 to 12 mm. and are composed of cords of chromaffin cells intermingled with strands of connective tissue, the whole being surrounded by a connective tissue capsule. After birth the chromaffin bodies degenerate, but do not disappear entirely.

Glomus Caroticum. — Associated with the intercarotld sympathetic plexus is a highly vascular chromaffin body known as the carotid gland. Its anlage has been first observed in 20 mm. embryos.

The Suprarenal Gland is developed from chromaffin tissue which becomes its medulla, and from mesodermal tissue which gives rise to its cortex. In an embryo of 6 mm. the anlage of the cortex is present, according to SouUt, and is derived from ingrowing buds of the coelomic epithelium. At 8 mm. the glands are definite organs and at 9 mm. their vascular structure is evident. The cellular elements of the cortex are at first larger than the chromaffin cells which give rise to the medulla. The ardages of the glands form projections in the dorsal wall of the ccelom between the mesonephros and mesentery (Figs. 221, 232 and 233).

The chromaffin cells of the medulla are derived from the cceliac plexus of the sympathetic system. In embryos of IS to 19 mm. (Fig. 368) masses of these cells begin to migrate from the median side of the suprarenal anlage to a central position, and later surround the central vein which is present in embryos of 23 mm. The primitive chromaffin cells are small and stain intensely. They continue their immigration until afUr birth. The differentiation of the cortex into its three characteristic layers is not completed until between the second and third years. The inner reiicular zone is formed first, next \h^ Jasciculate zone, and last the glomerular zone.

Fig. 367 .^Section through a chromatfin body in a 44 nun. human fetus (after Rohn). X 450. p, Mother chromaffin cells; sy, sympathetic cells; 6, blood vessel.

37°

When the cells of the medulla begin to produce an internal secretion thqr I give the chrome reaction. By using extract of the aortic bodies, which are « tirely composed of chromaffin cells. Biedl and Wiese! have proved that its eSec^a like that of adrenalin, is to increase the blood pressure. The logical conclusion ub that the effect of adrenalin, an extract of the suprarenal glands, is due lo SOLf internal secretion produced by the chromaffin cells of the suprarenal medulla.

Fig. J68. — Transverse Biyce). sy. Sympathetic cells; gland.

Portions of the suprarenal aniage may be separated from the parent glnnd and (omi accessory suprartnals. As a rule, such accessor>- glaods are composed only of conical sub- i stance; they may migrate some dialance from their original position, accompanying the I genital glands. In fishes the cortex and medulla perast normally as separate organs.

E. DEVELOPMENT OF THE SENSE ORGANS

The sense cells of primitive animals (e. g.. worms) are ectodermal in orij

and position. Only those of the vertebrate olfactory organ have retained thi$s

primitive relation. During phylogeny the cell-bodies of all other such priman

sensor>- neurones migrated inward to form the dorsal ganglion (Pariter), hei

their peripheral processes either end freely m the epithelium or appropriate new cells to serve as sensory receptors (taste, hearing).

The nervous structures of the sense organs consist of the general sense organs of the integument, muscles, tendons, and viscera, and of the special sense organs which include the taste buds of the tongue, the olfactory epithelium, the retina, optic nerve and lens of the eye, and the epithelial lining of the ear labyrinth.

L General Sensory Organs

Free nerve ierminaiians form the great majority of all the general sensory organs. When no sensory corpuscle is developed, the neurofibrils of the sensory nerve fibers separate and end among the cells of the epithelia.

Lamellated corpuscles first arise during the fifth month as masses of mesodermal cells clustered aroimd a nerve termination. These cells increase in number, flatten out, and give rise to the concentric lamellae of these peculiar structures. In the cat these corpuscles increase in number by budding.

The tactile corpuscles, according to Ranvier, are developed from mesenchymal cells and branching nerve fibrils during the first six months after birth.

n. Taste Buds

The anlages of the taste buds appear as thickenings of the lingual epithelium in 110 mm. (C H) fetuses (Graberg). The cells of the taste bud anlage lengthen and later extend to the surface of the epithelium. They are differentiated into the sensory taste cells, with modified cuticular tips, and into supporting cells. The taste buds are supplied by nerve fibers of the seventh, ninth, and tenth cerebral nerves; the fibers branch and end in contact with the periphery of the taste cells.

In the fetus of five to seven months taste buds are more widely distributed than in the adult. They are foimd in the walls of the vallate, fungiform, and foliate papillae of the tongue, on the under surface of the tongue, on both surfaces of the epiglottis, on the palatine tonsils and arches, and on the soft palate. After birth many of the taste buds degenerate, only those on the lateral walls of the vallate and foliate papillae, on a few fungiform papillae, and on the laryngeal surface of the epiglottis persisting.

m. The Olfactory Organ

The olfactory epithelium arises as paired thickenings or placodes of the cranial ectoderm (Fig. 369 A ) . The placodes are depressed to form the olfactory pitSf or fossce, about which the nose develops (Fig. 89).

In embryos of 4 to 5 mm, (Fig. 369) the placodes are sharply marked off from Ihe surrounding ectoderm as ventro-lateral thickenings near the top of the bead. They are flattened and begin to invaginate in embryos of 6 to 7 mm. In 8 embryos the invagination has produced a distinct pit, or fossa, surrounded everywhere save ventraily by a marginal swelling.

The later development of the olfactory organ is associated with that of the face. It will be remembered (cf. p. 145) that the first branchial arch forks into | the maxillary and mandibular processes. Dorsal to the oral cavity is the fronto

Fic. JW— Sections ih (X 13); C*

Lai. Kosat proem Mrd. nasal prnrtss iloxillary procrss

Epilketi.ll plaSe

li the oi&ctory anlages of human embn'os. A, 4.9 nun. (X 20): B, fi-Sn m. {X 13); D and £. 10 mm. (.1, B and C from Kicbel and Hie.)

nasal process of the head, lateral to it the maxillary processes, and \'entral to it are the mandibular processes (Fig. 97). With the development of the nasal pits the fronto-nasal process is divided into paired laUral nasal processes and a single > median frontal process, from which are differentiated later the median nasal ffroc- ] esses, or processus globulares (Fig. 370). Thf nasal pits are at first grooves, each bounded mesially by the median frontal process and laterally by the lateral nasal process and the maxillary process (Fig. 370 .4). The fusion of the maxillary processes with the ventro-lateral ends of the median frontal process converts the

DEVELOPUENT OF THE SENSE QKOAMK

373

nasal grooves into blind pits or fosse, shutting them off from the mouth cavity (Fig. 370). Thus in embryos of 10 to 12 mm. the nasal fossa has but one opening, the external naris, and is separated from the mouth cavity by an ectodermal plate (Fig. 369 D, E).

The ventro-lateral ends of the median frontal process enlarge and become the median nasal processes which fuse with the lateral nasal processes and reduce the size of the external nares (Fig. 370 B). Externally, the nares are now bounded ventrally by the fused nasal processes. The epithelial plates which sq)arate the nasal fosse from the primitive mouth cavity become thin membra

Fio. 370.— Two stages in the development of the jaws and nose. A , Ventral view of the end of the head of a 10.5 nun. human embryo (after Peter) i S, of an 11 .3 mm. embryo (after RabI).

nous structures caudally, and, rupturing, produce two internal nasal openings, the primitive choana (Fig, 153). Cranially, the epithelial plate fc destroyed by ingrowing mesoderm of the maxillary process and median nasal process which replaces it, thereby forming the primitive palate (Fig. 369 D). The primitive palate forms the Up and the premaxillary palate. The nasal fosse now open externally through the external nares and internally into the roof of the mouth cavity through the primitive choana.

Coincident with these changes the median frontal process has become relatively smaller and that portion of it between the external nares and the nasal fosse becomes the nasal septum (Fig. 370). As the fadal region grows and elongates, the primitive cboanx become longer and form slit-like openings in the roof of the mouth cavity. By the development and fusion of the palatine processes (described on p. 147) the dorsal portion of the mouth cavity is separated off and constitutes the nasal passages (cf. Figs. 371 and 373). The nasal passages of the two sides for a lime communicate thrcsugh the space between the hard palate and the nasal septum. Later, the ventral border of the septum fuses with the hard palate and completely separates the nasal passages (Fig. 372). The nasal passages of the adult thus consist of the primitive nasal fossse plus a portion

Olfadory epilkelium Vomero-natal oigiin ^

Dental (,i«inu—

Meckel's earlilnfe

Fio. 37 L— Transversa ^.eaiim ihro embryo. In the nasal seplum is

il pas&agc<> anil jiabiine i)r<tcesses of a 20 mm. human on of the vomero-nasal organ (of Jacobson). X 30.

of the primitive mouth cavity which has been appropriated secondarily by the development of the hard palate. The passages of the adult thus open caudally by secondary choana into the cavity of the pharynx.

Part of the epithelium which lines the nasal fossfe is transformed into the sensory olfactory epithelium (Fig. 371). The remainder covers the concha: and lines the vomero-nasal organ (of jacobson), the ethmoidal cells, and the cranial sinuses.

The Vomero-nasal Organ {of Jacobson) is a rudimentary epithelial structure which first appears in 8.5 to 9 mm. embryos on the median wall of the nasal fossa

DEVELOPMENT OF THE SENSE ORGANS

375

(Fig, 369 C, E). The groove deepens and closes caudally to form a tubular structure in the cranial portion of the nasal septum (Fig. 371). During the sixth month it attains a length of 4 mm. Nerve fibers, arising from cells in its epithelium . join

Fig. 372. — Transverse section through the nasal passages of a 65 mm. human fetus. X 14.

the olfactory nerve, and it also receives fibers from the n. terminalis. In late fetal stages it often degenerates, but may persist in the adult (Merkel, Mangakis).

Harizonliil elhmnid plait

— /Mirral lo

Fig. 373.— Right naul passage of a fetus at tenn (after Killian). /, MuUlo-tuihinal; II-VI, ethmoturbinals. The slight clevatioD at the left of / and // is the naso-turhinal.

Special cartilages are developed for its support (Fig. 371). The organ of Jacobson is not functional in man, but in many animals evidently constitutes a spedat olfactory organ.

376

The Conchas are structures which are poorly developed in man. Tliey ap-1 pear on the lateral and median walls of the primitive nasal fosss. The inferior I concha, or maxillo-lurbinal. is developed first in human embryos (Figs. 371 and | 372), It forms a ridge along the caudal two-thirds of the lateral wall and is I marked off by a ventral groove which becomes the inferior nasal meatus (Fig. 373). The naso-lurhinal is very rudimentary and appears as a slight elevation dorsal and cranial to the inferior concha (Fig. 373). Dorsal to the inferior concha arise five dbmo-turbinals. which grow progressively smaller caudaUy. According to Peter, the ethmo-turbinals ansi il wall of the nasal fossa, and, by

a process of unequal growth, are tranai„. .o the lateral wall (Fig. 372), Acccs- , sory concha; are also developed (Killian),

In adult anatomy, the inferior concha forms from / (Fig. 373), the middle concha Iroux I //, and the superior concha from /// and IV.

In addition to the ridges formed by the concha;, there are developed in the grooves J

t'thtno-turbinals the ethmoidal cells. between / anri //, Fig. 373) gives rise to Vne frontal Ji lary sinus grows out from the inferior recess of the sa nasal fossa becomes the sphenoidal sinus, which, as

The cells of the olfactory epithelium become ciliated, but only a small area, representin the primitive epithelial invagination, functions as an olfactory sense organ. The olfaetoryl cells of this area give rise to the libers which constitute the olfactory nerve (cf. p. 357).

' birth the frontal recess (localedi|

(J. During the third month ihe n.

e groove. The most caudal end of ihsl

■£, invades the sphenoiil'l

IV. The Development of the Eye

The anlage of the human eye appears in embryos of 2.5 mm. as a thickeningj and evagination of the neural plate of the fore-brain. At this stage the neural '

groove of the fure-brain has not closed optic vesicles are larger, but still may brain cavity (Fig. 374 A, B). ^ vesicle is attachefl to the ven

The thickening, flatteni ;, i the optic vesicle gives rise to me tion also extends ventrally along the >. j„ the chorioid fissure (Figs. 331, 375 and

At the same time that the optic vesicle ib ectoderm overlying the former thickens, as see plale, or optic placode. This plate invaginates opening of which closes in embryos of 6 to 7 i lens vesicle, which remains at first attached to

U, 330 and 382). At 4 mm. the ctcd by a wide opening with the I shown in Fig. 374 C, the optic , distinct optic stalk (cf. Fig, 343). n of the distal and ventral wall of 174 B-D). The area of invaginaand produces a groove known as

DEVELOPMENT OF THE SENSE ORGANS

embryo of 10 mm. (Fig. 376) the lens vesicle has separated from the ectoderm, which will form the epithelium of the coraea. The lens vesicle in earlier stages

—Stages in Uie early devdopment of the buin&n eye. A, B,at 4 mm. (X 27); C, a 23); D. at 6.25 mm. (X 18) (after Kdbel and Elze).

a.(X

{Fig. 374 D) is closely applied to the inner wall of the optic cup, but now it has separated from it, leaving a space in which the vitreous body is developing. The inner retinal layer of the optic cup has become very thick and is appUed to the outer layer, so that the cavity of the primi- j^. tive optic vesicle is nearly obliterated (Fig. 376). Pigment granules have begun to appear in the outer cells which form the pigment layer oi the retimt. Mes- of,iu uaik

enchymal tissue surrounds the FiG.37S.-The optic stalk, cup and lw» of a human

optic cup and is beginning to embryo of 12.5 mm. The chotioid fissure has not yet ex, . , , , tended along the cqjtic stalk (from Fuchs, after Hocb++++make its way between the lens .tetter), x 90++++vesicle and the ectoderm. Here

the anterior chamber of the eye develops later as a deft in the mesoderm. The

distal mesenchymal tissue (next the ectoderm) forms the substantia propria of the

Mcsentkyma Lens vesicle VUrtous body OpHc stalk Opfk ri

^^W

mm^

s^P^

IM

p^Sj

^^

i^^9

Iw

i'^'^

i^

^^B

%

r

m

Epilkelium of cornea Pigmml laytr ofrtrm Nenous layer of et na

Fig. 376. — A transverse section through the optic cup stalk and lens of a 10 mm human embryo.

Epithelial layer t^ lens Pigment layer of the rt

Ectoderm

Fio. 377. — Transverse section passing through the optic cup at the level of the chorioid fissure. The central artery of the retina is seen entering the fissure and sending a branch to the proximal surface of the lens; from a 12.5 mm. human embryo. X 105.

cornea and its posterior epithelium, while the proximal mesenchyma (next the lens) differentiates into the vascular capsule of the lens. The mesenchyme surrounding the optic cup is continuous with that which forms the cornea and later

DEVELOPMENT OF THE SENSE ORGANS

379

gives rise to the sclerotic layer, to the chorioid layer, and to the anterior layers of the dtiary body and iris.

Both the inner and outer layers of the optic cup are continued into the optic stalk, as seen in Fig. 376, This is due to the trough-like invagination of the ventral wall of the optic stalk, the chorioid fissure, when the optic vesicle is transformed into the optic cup (Fig. 375), Into the chorioid fissure grows the central artery of the retina, carrying with it into the posterior cavity of the eye a small amount of mesenchyme (Fig. 377). Branches from this vessel extend to the posterior surface of the lens and supply it with nutriment for its growth. At a later stage the chorioid fissure EtrUhdial Una

closes, so that the distal rim of the optic cup forms a complete circle.

If the chorioid fissure fails to close, the optic cup remains open at one point and this results in the defective developmcnl of the iris, ciliary body, and chorioid layer. Such a defect is known as coloboma.

The old view that the development of the lens vesicle causes the formation of the optic cup by pushing in its distal wall has been disproved by W. H, Lewb, for if an aniage of the optic vesicle from an amphibian embryo be transplanted to some other part of the embryo, it can develop into an optic cup in the absence of a lens. Furthermore, it is the contact of optic vesicle with ectoderm that furnishes the stimulus for lens fonnalion, both normally and after transplantation to foreign regions, e. g., abdomen.

The lens vesicle, and its early development from the ectoderm, have been described. Its proximal wall is much thickened in 10 mm. embryos, and these cells form the lens fibers (Fig. 376) which will soon obliterate the cavity of the vesicle, as in embryos of 15 to 17 mm. (Fig. 378). The cells of the distal layer remain of a low columnar type and constitute the epithelial layer of the lens. When the lens fibers attain a length of 0.18 mm. they cease forming new fibers by cell division. New fibers thereafter arise from the cells of the epithelial layer at its line of union with the lens fibers. The nuclei are arranged in a layer convex toward the outer surface of the eye and later degenerate, the degeneration begin

Eclodrrm

Pig. 378.^ — Section through the lens and corneal e derm of a 16 mm. pig embryo. X. 140.

380 THE PEEIPHEllAL NERVOUS SYSTEM

ning centrally. Lens sutures are formed on the proximal and distal faces of the lens when the longer newly formed peripheral fibers overlap the ends of the shorter central fibers. By an intricate but orderly arrangement of fibers these sutures are later transformed into lens-stars of three, and finally of six or nine rays (Fig. 379). The structureless capsule of the lens is probably derived from the lens cells. The lens, at first somewhat triangular in cross section, becomes nearly spherical at three months (Fig. 379).

Poslmor epukdntm

The origin of the vitreous body has been in doubt, one view deriving it from the mesenchyma which enters the optic cup through the chorioid fissure and about the edge of lens, another view holding that it arises from cytoplasmic processes of cells in the retinal layer.

It is certain that the vitreous tissue is formed before mesenchyma is present in the cavity of the optic cup. Szily {Anat. Hefte, Bd. 35, 1908) regards this primitive vitreous body as a

DEVELOPMENT OF THE SENSE ORGANS 381

derivative of both retinal and lens cells, it forming a non-cellular network of cytoplasmic processes which are continuous with the cells of the lens and retina. With the ingrowth of the central artery of the retina, from which the artery of the lens passes to the proximal surface of the lens and branches on it, a certain amount of mesenchymal tissue invades the optic cup, and this tissue probably contributes to the development of the vitreous body (Fig. 377). The vitreous body may therefore be regarded as a derivative both of the ectoderm and of the mesoderm.

The mesenchyma accompanying the vessels to the proximal surface of the lens, and that on its distal surface, give rise to the vascular capsule of the lens (Fig. 377). On the distal surface of the lens this is supplied by branches of the anterior dliary arteries and is known as the pupillary membrane; the vessels disappear and the membrane degenerates just before birth. The artery of the

Fk. 380.— Section of the nervous layer of the retina from a diagiaimnaticaUy the cellular elements of the rel

mm. human fetus. At the left is shown according to Cajal. X 440.

lens also degenerates, its wall persisting as the transparent hyaloid canal. Fibrillae extending in the vitreous humor from the pars cilia ta of the retinal layer to the capsule of the lens persist as the zonula ciliaris or suspensory ligament of the lens.

Differentiation of the Optic Cup.— We have seen that of the two layers of the optic cup the outer becomes the pigment layer of the retina. Pigment granules appear in its cells in embryos of 7 mm. and the pigmentation of this layer is marked in 12 mm. embryos (Fig. 377).

The inner, thicker layer of the optic cup, the retinal layer, is subdivided into a distal zone, the pars caca, which is non-nervous, and into the pars optica, or the nervous retina proper. The line of demarcation between the pars optica and the pars oeca is a serrated circle, the ora serrata. The blind portion of the retinal layer, the pars caca, with the development of the ciliary bodies is differentiated

Otdtr nuclear layer

i4— Outer reticular layer

Inner nuclear layer

Inner reikular layer

into a pars ciliarts and pars iridis retina. The former, with a cx>rresponding zone of the pigment layer, covers the ciliary bodies. The pars iridis forms the proximal layer of the iris and blends intimately with the pigment layer in this region, its cells also becoming heavily pigmented (Fig, 379),

The pars optica, or nervous portion of the retina, begins to difTerentiate proximaljy. the differentiation extending distally. An outer cellular layer and an \nncT fibrous layer may be distinguished in 12 mm. embryos (Fig. 377), These

correspond to the cellular layer (ependymal and mantle zones) and marginal layer of the neural tube. In fetuses of 65 mm. (C R) the retina shows three layers, large ganglion cells having migrated in from the outer cellular layer of rods and cones (Fig. 380). In a fetus of the seventh month all the layers of the adult retina may be recognized (Fig. 381). As in the wall of the neural tube, there are differentiated in the retina supporting tissue and nervous tissue. The supporting elements, or fibers of Mailer, resemble ependymal cells and are radially arranged (Figs. 380 and 381). Their terminations form internal and external limiting membranes.

The neuroblasts of the retina differentiate into an outer layer of rod and cone cells, the visual cells of the retina, which are at first unipolar (Fig. 381). Internal to this layer are layers of bipolar and multipolar cells. The inner layer of multipolar cells constitutes the ganglion cell layer. Axons from these cells form the inner nerve fiber layer of optic fibers. These converge to the optic stalk, and, in embryos of 15 mm., grow back in its wall to the brain. The cells of the optic stalk are converted into neuroglia supporting tissue and the cavity of the stalk is gradually obliterated. The optic stalk is thus transformed into the optic nerve

cell layer

'Interitai limiting membrane

DEVELOPMENT OF THE SENSE ORGANS 383

The Sclerotic and Chorioid Layers, and their Derivatives. — After the mesenchyme grows in between the ectoderm and the lens (Fig. 377), the lens and optic cup are surrounded by a condensed layer of mesenchymal tissue, which gives rise to the supporting and vascular layers of the eyeball. By condensation and differentiation of its outer layers, a dense layer of white fibrous tissue is developed, which forms the sclerotic layer. This corresponds to the dura mater of the brain. In the mesenchyme of 25 mm. embryos a cavity appears distally which separates the condensed layer of mesenchyme continuous with the sclerotic from the vascular capsule of the lens (Fig. 379). This cavity is the anterior chamber of the eye and separates the anlage of the cornea from the lens capsule.

An inner layer of mesenchyme, between the anlage of the sclerotic and the pigment layer of the retina, becomes highly vascular during the sixth month. Its cells become stellate in form and pigmented, so that the tissue is loose and reticulate. This vascular tissue constitutes the chorioid layer, in which course the chief vessels of the eye. The chorioid layer corresponds to the pia mater of the brain. Distal to the ora serrata of the retinal layer the chorioid is differentiated: (1) into the vascular folds of the ciliary bodies; (2) into the smooth fibers of the ciliary muscle; (3) into the stroma of the iris. The proximal pigmented layers of the iris are derived from the pars iridis retinae and from a corresponding zone of the pigment layer. Of these, the pigment layer cells give rise to the sphincter and dilator muscles of the iris. These smooth muscle fibers are thus of ectodermal origin.

The Eyelids appear as folds of the integument in 20 mm. embryos. The lids come together and the epidermis at their edges is fused in 33 mm. embryos (Fig. 379). Later, when the epidermal cells are cornified, separation of the eyelids takes place. A third rudimentary eyelid, corresponding to the functional nictitating membrane of lower vertebrates, forms the plica semilunaris. The epidermis of the eyelids forms a continuous layer on their inner surfaces known as the conjunctiva^ which in turn is continuous with the anterior epithelium of the cornea.

The Eyelashes, or cilia y develop like ordinary hairs and are provided with small sebaceous glands. In the tarsus, or dense connective tissue layer of the eyelids, which lies close to the conjunctival epithelium, there are developed about 30 tarsal (Meibomian) glands. These arise as ingrowths of the epithelium at the edges of the eyelids, while the latter are still fused.

The Lacrimal Glands appear in embryos of about 25 mm., according to Keibel and Elze. They arise as five or six ingrowths of the conjunctiva, dorsally and near the ext.:mal angle of the eye. The aniages are at first knob-like, but rapidly lengthen into solid epithelial cords. They begin to branch in 30 mm. embryos. At stages between 50 and 60 mm. (C R) additional aniages appear which also branch.

In 38 mm, (C R) embryos a septum begins to partition the gland into orbital and palpebral portions. This septum is complete at 61) mm. (C R), the five or six aniages first developed constituting the peripheral orbital part. Lumina appear in the glandular cords in fetuses or 50 mm. {C R) by the degeneration of the central cells. Accessory lacrimal glands appear in 300 mm. (C R) fetuses. The lacrimal gland Ls not fully diflercntiated at birth, being only one-third the size of the adull gland. In old age marked degcueration occurs.

The NasO'lacrimal Duct arises in 12 mm. embryos as a ridge-like thickening of the epithelial lining of the naso-lacrimal groove (Fig. 149), which, it will be remembered, extends from the inner angle of the eye to the olfactory fossa. This thickening becomes cut off, and, as a solid cord, sinks into the underlying mesoderm (Schaeffer). Secondary sprouts growing out from this cord to the eyelids form the lacrimal canals. A lumen, completed at birth, appears during the third month {Fig. 372).

V. The Development of the Ear

The human ear consists of a sound-conducting apparatus and of a receptive organ. The conveyance of sound is the function of the external and middle ears.

Iliad-brain

A ttdilory ganglion A udilory placode

Fig. .^R2. — Two stagei in the early dcvclo[jiiie i< I

Horizontal section through the head sjid opm m auditory placode and ganglion (X 27); B, section tlirougn human embryo (X 33).

The end organ proper is the inner ear with the cochlear duct. Besides this acoustic function tb ear acts as an organ of equilibration.

DEVELOPMENT OF THE SENSE OSGANS 385

The Inner Ear. — The epithelium of the internal ear is derived from the ectoderm. Its first anlage appears in embryos of 2 mm. as a thickened ectodermal

Fig. 383.— Four EIze). X about 30. r-c. vesicle; Near. 4, i\eur. 5,

vesicle of a 4 mm. human embryo (after Keibel and tbe anlage of the endolymph duct and sac; a.v., otic four and five of the myelencephalon.

plate, the auditory placode (Fig. 382 A). These are developed dorsal to the second branchial grooves, at the sides of the hind bram opposite the fifth neuromeres (Fig. 383). The placodes are invaginated to form hollow vesicles which close in embryos of 2.5 to 3

Wali oj mydencepkaion—

mm., but remain temporarily attached to the ectoderm (Fig. 382 B).

The auditory vesicle, or otocyst, when closed and detached, is nearly spherical, but approximately at the point where it was attached to the ectoderm a recess, the ductus enddymphUicus, is formed. The point of origin of this recess is shifted later from a dorsal to a mesial position (Figs. 384 and 385 o). The endolymph duct corresponds to that of selachian fishes, which remains permanently open to the exterior- In man, its extremity is closed and dilated to form the endolymphatic sac (Fig. 385 e).

The differentiation of the auditory vesicle has been described by His. Jr.. and more recently by Streetcr (Amer. Jour. Anat., vol, 6, 1906). In an embryo of about 7 mm. the vesicle has elongated, its narrower ventral process con

Fig. 3S4.— Right half of a tmisverse sect on through tbe hind-brain and ot c %es cle showing the position of the endolymph duct From a human embryo 69 mm long (His).

stituting the anlage of the cochlear duel (Fig. 385 a). The wider, dorsal portion of the otocyst is the vestibular anlage, which shows indications dorsaUy of the developing semicirciJar canals. These are formed in 11 mm. embryos as two pouches — the anterior and posterior canals from a single pouch at the dorsal border of the otocyst, the lateral canal later from a lateral outpocketing (Fig. 385 c). Centrally the walls of these pouches flatten and fuse to form epithelial plates. In the three plates thus produced canals are left peripherally, communicating with the cavity of the vestibiJe. Soon the epithelial plates are resorbed, leaving the semicircular canals as in Fig. 385 d, e. Dorsally a notch separates the anterior and posterior canals. Of these canals, the anterior is completed before the posterior. The lateral canal is the last to develop.

In a 20 mm. embryo (Fig. 385 e) the three canals are present and the cochlear duct has begun to coil like a snail shell. It will be seen that the anterior and posterior canals have a common opening dorsally into the vestibiJe, while their opposite ends and the cranial end of the lateral canal are dilated to form ampulla. In each ampulla is located an end organ, the crista ampuUaris, which will be referred to later. By a constriction of its wall the vestibule is differentiated into a dorsal portion, the utriculus, to which are attached the semicircular canals, and a ventral portion, the sacculus, which is connected with the cochlear duct (Fig. 385 e,f). At 30 mm. the adult condition is nearly attained. The sacculus and utriculus are more completely separated, the canals are relatively longer, their ampullae more prominent, and the cochlear duct is coiled about two and a half turns (Fig. 385/). In the adult, the sacculus and utriculus become completely separated from each other, but each remains attached to the endolymph duct by a slender canal which represents the prolongation of their respective walls. Similarly, the cochlear duct is constricted from the sacculus, the basal end of the former becomes a blind process, and a canal, the ductus reunienSy alone coimects the two.

The epithelium of the labyrinth at first is composed of a single layer of low columnar cells. At an early stage, fibers from the acoustic nerve grow between the epithelial cells in certain regions and these become modified to produce special sense organs. These end organs are the cristce amptUlares in the ampullae of the semicircular canals, the maculm acusticce in the utriculus and sacculus, and the spiral organ (of Corti) in the cochlear duct.

The cristas and maculae are static organs, or sense organs for maintaining equilibrium. In each ampulla, transverse to the long axis of the canal, the epithelium and underlying tissue form a curved ridge, the crista. The cells of the

f.jonun lateral

l-'ii;. ,iS.i.— Six slap,-s in Ihe ilfvclnjinicnt of the itiltrnal tar (Sln-etcr). X 2.1. The fiKun's -hiuv Inlrnil views <if mix Ids < if llu- lid mt-mbni nous bl>yHmh--ci ul (>.6 mm.; ft at <> mm.; <-nl t1 mm.; dm 1.1 mm.: r m 20 mm., ami / al Mi mm. The nilors ycllun' ami ml are used 1<> iniliiatc n>|M.Ttivcly the (-(H'hirar nml \'cstil>uliir divtsions of the onnistic nene nnd its ininulia. ahunrf. fixur, .\iva of wall where al>-<iqition is etwnpl<-le; trus, ems eiimmuw: r. v. l-il., liuctus semieirruliiris luleralis: c .>i'. pi"/., (luelus -rmicireularis iHisterior: r. v..<ii^.. iluetus >emii-ireiilaris sujierior or anterinr; niUni, i\urt\\^ eiH-hlearis; i.kA. pinifA.iiHhlfar nnloKf; rwrfi'/vmf*., a])[>i'niiix eniiulymiihatieus: iini„ saeriiliis; tiir. ,«rfW., saceiis t'n<1»1ym[>hailrusi \inus h(. /.i(., siiuis iiirieuli Lili^ralis: iilrif., tilriitiliis.

DEVELOPMENT OF THE SENSE ORGANS 387

epithelium are differentiated: (1) into sense cells with bristle-like hairs at their ends, and (2) into supporting cells. About the bases of the sensory cells nerve fibers from the vestibular division of the acoustic nerve branch. The macular resemble the cristae in their development save that larger areas of the epithelium are diflferentiated into cushion-like end organs. Over the maculae concretions of lime salts may form otoconia which remain attached to the sensory bristles.

The true organ of hearing, the spircU organ, is developed in the bascU epithelium of the cochlear duct, basal having reference here to the base of the cochlea. The development of the spiral organ has been studied carefully only in the lower mammals. According to Prentiss (Amer. Jour. Anat., vol. 14, 1913) in pig embryos of 5 cm. the basal epithelium is thickened, the cells becoming highly columnar and the nuclei forming several layers. In later stages, 7 to 9 cm., inner and outer epithelial thickenings are differentiated, the boundary line between them being the future spiral tunnel (Fig. 386 ^4). At the free ends of the cells of the epithelial swellings there is formed a cuticular structure, the membrana tectoria^ which appears first in embryos of 4 to 5 cm. The cells of the inner (axial) thickening give rise to the epithelium of the spiral limbus, to the cells lining the internal spiral sulcus J and to the supporting cells and inner hair cells of the spiral organ (Fig. 386 By C). The out^r epithelial thickening forms the pillars of Corti, the outer hair cells, and supporting cells of the spiral organ. Differentiation begins in the basal turn of the cochlea and proceeds toward the apex. The internal spiral sulcus is formed by the degeneration and metamorphosis of the cells of the inner epithelial thickening which lie between the labium vestibulare and the spiral organ (Fig. 386 B, C). These cells become cuboidal, or flat, and line the spiral sulcus, while the membrana tectoria loses its attachment with them. The membrana tectoria becomes thickest over the spiral organ and in full term fetuses is still attached to its outer cells (Fig. 386 C).

Hardesty (Amer. Jour. Anat., vol. 18, 1915), on the contrary, asserts that the membrana tectoria is not attached permanently to the cells of the spinal organ.

From what is known of the development of the spiral organ in human embryos, it follows the same lines of development as described for the pig. It must develop relatively late, however, for in the cochlear duct of a newborn child figured by Krause the spiral sulcus and the spiral tunnel are not yet present.

The mesenchyme surrounding the labyrinth is differentiated into a fibrous membrane directly surrounding the epithelium, and into the perichondrium of the cartilage which develops about the whole internal ear. Between these two is a more open mucous tissue which largely disappears, leaving the perilymph

Fig. 386. — Three staets in ihc dilTertntiation of the basai epithelium of the cochlear duct to form the s;>iral ori;an (of Corti), internal spiral sulcus and labium vestibulare. .1. Section through the cochlear duct of an 8,5 cm. pig fetus (X 120); B, the same from a 20 cm, fetus (X 140); C, from a 30 cm. fetus (near term] (X HO), rp.s.np.. Epithelium of spiral sulcus; /i,f., hair cells; i.cp.c, inner epithelial thickening; i.h.c., inner hair cells; i.pil.. inner pillar of Corti: l>ib. test,, labium vestibulare; limb, sp., limbus spiralis; m. hm., basilar membrane; m. lecl.. membrana tectorial m. veil., vestibular membrane; n. cwA., cochlear division of acoustic nerve; o.rp-c, outer epithelial thickeninR; o.h.c., outer hair cells; s.sp., sulcus spiralis; sc.lymp., scala timpani; si. II.. strij>e of Hcnsen: l.sp., spiral tunnel.

Space. The membranous labyrinth is thus suspended in the fluid of the perilymph space. The bony labyrinth is produced by the conversion of the cartilage capsule into bone. In the case of the cochlea, large perilymph spaces form above and below the cochlear duct. The duct becomes triangular in section as its lateral wall remains attached to the bony labyrinth, while its inner angle is adherent to the modiolus. The upper perilymph space is formed first and is the scala vestibuliy the lower space is the scala tympani. The thin wall separating the cavity of the cochlear duct from that of the scala vestibuli is the vestibular membrane (of Reissner). Beneath the basal epithelium of the cochlear duct a fibrous structure, the basilar membrane, is differentiated by the mesenchyme. The modiolus is not preformed as cartilage, but is developed directly from the mesenchyme as a membrane bone. The development of the acoustic nerve has been described on page 358 with the other cerebral nerves.

The Middle Ear. — The middle ear cavity is differentiated from the first pharyngeal pouch which appears in embryos of 3 mm. The pouch enlarges rapidly up to the seventh week, is flattened

horizontally, and is in contact with the Malleus

ectoderm (Fig. 168). During the latter ^MMtrL.e) part of the second month, in embryos f^

of 24 mm., the wall of the tympanic

cavity is constricted to form the auditory Tympanum^^ _^,,,jr ^^^^c

(Eustachian) lube. This canal lengthens ^ ^- O'fch II

(ReicherVs cartilage)

and its lumen becomes slit-like during r^ -.on ^' x. - ». u i.. i

• =• r IG. 387 — Diagram snowing the branchial the fourth month. The tympanic cavity arch origin of the auditory ossicles.

is surrounded by loose areolar connective tissue in which the auditory ossicles are developed and for a time are embedded. Even in the adult, the ossicles, muscles, and chorda tympani nerve retain a covering of mucous epithelium continuous with that lining the tympanic cavity. The pneumatic cells are formed at the close of fetal life.

The development of the auditory ossicles has been described by Broman (Anat. Hefte, Bd. 11, 1899), with whose general conclusions most recent workers agree. The condensed mesenchyma of the first and second branchial arches gives rise to the ear ossicles.

The malleus and incus are differentiated from the dorsal end of the first arch (Fig. 387). The cartilaginous anlage of the malleus is continuous ventrally with MeckePs cartilage of the mandible. Between the malleus and incus is an intermediate disk of tissue, which later forms an articulation. When the malleus begins to ossify it separates from Meckel's cartilage. The incus is early connected with the anlage of the slopes, and the connected portion becomes the cms tongum. Between this and the stapes an articulation develops.

The stapes and Reichert's cartilage are derived from the second branchial arch (Fig. 387). The mesenchymal anlage of the stapes is perforated by the stapedial artery, and its cartilaginous anlage is ring-shaped. This form persists until the middle of the third month, when it assumes its adult structure and the stapedial artery disappears.

Kii;. .18S. — StaResin the development of the auricle. (Adapted in part after Hb). .4,11 mm.; B,

13.6 mm.; C, 15 mm.; D, adult. 1, 2, 3, clt:\-ations on the mandibular arch; 4, 5, 6, elevations on the hyoid urch; af, auricular fold; ov, otic vesicle; 1, tragus; 2, 3, helix; 4, 5, antihelii; 6, antitiagus.

The muscle of the malleus, the tensor tympani. is derived from the first branchial arch; the sliipfdial muscle from the second arch. The further fact that these muscles are innervated by ihe trigeminal and facial nerves, which arc the nerves of the first and second arches respectively, points toward a similar origin for the ear ossicles.

Fuths, studying rabbit embryos, on the contrary, concludes: (I) the stapes is derived from the capsule of the labyrinth; (2) the malleus and incus arise independently of the first branchial arch.

The External Ear. — The external ear is developed from and about the first ectoticrmal branchial groove. The auricle arises from six elevations which appear, three on the mandibular, and three on the hyoid arch (Fig. 388). Modem accounts of the transformation of these hillocks into the adult auricle agree in the main.

Caudal to the hyoid anlages a fold of the hyoid integument is formed, the auricidar fold or hyoid helix. A similar fold forms later, dorsal to the first branchial groove, and imites with the auricular fold to form with it the free margin of the auricle. The point of fusion of these two folds marks the position of the satyr tubercle, according to Schwalbe. Darwin^s tubercle appears at about the middle of the margin of the free auriciJar fold, and corresponds to the apex of the auricle in lower mammals. The tragus is derived from mandibular hillock 1 ; the helix from mandibiJar hillocks 2 and 3; the antihelix from hyoid hillocks 4 and 5; the antitragus from hyoid hillock 6. The lobule represents the lower end of the auricular fold.

The external auditory meatus is formed as an ingrowth of the first branchial groove. In embryos of 12 to 15 mm. the wall of this groove is in contact dorsally with the entoderm of the first pharyngeal pouch. Later, however, this contact is lost, and during the latter part of the second month, according to Hammar, an ingrowth takes place from the ventral portion of the groove, to form a funnelshaped canal.

The lumen of this tube is temporarily closed during the fourth and fifth months, but later re-opens. During the third month a cellular plate at the extremity of the primary auditory meatus grows in and reaches the outer end of the tympanic cavity. During the seventh month a spaqe is formed by the splitting of this plate, and the secondary inner portion of the external meatus is thus developed.

The tympanic membrane is formed by a thinning out of the mesodermal tissue in the region where the wall of the external auditory meatus abuts upon the wall of the tympanic cavity. Hence it is covered externally by ectodermal, and internally by entodermal epithelium.

INDEX

Abdominal pregnancy, 20 Abducens nerve, 116, 361 Accessorius nerve, 116 Acoustic nerve, 92, 116, 358 Acrania, 352 Adipose tissue, 287 Adrenalin, 370 After pains, 241 After-birth, 242 Als nasi, 145

Alar plate, 323, 332, 335, 337 Allantoic stalk, 66, 97, 120

vessels 67 Allantois! 57, 66, 69, 74, 83, 93, 97 derivation of, 70, 74 section through. 111 Allelomorphs, 21 Alveoli of pancreas, 179 Alveolo-lingual gland, 152 Ameloblasts, 156 Amitosis, 12 Amnion, origin of, 65, 73

bat, 74

chick, 55, 62, 65

human, 71, 73

pig, 68 Amniotic fluid, 74 Amphiaster, 13

Amphibia, cleavage of ovum in, 25 gastrulation of, 28 origin of mesoderm in, 30 Amphioxus, cleavage of ovum in, 23 gastrulation of, 28 origin of mesoderm in, 29 Ampulla of ductus deferens, 218 Ansil membrane, 160, 205 Anaphase of mitosis, 13 Anchoring villi, 237 Angioblast, 39 chick, 42 human, 243 Animal pole, 23 Anlage defined, 3 Ansa hypoglossi, 355, 360 Antihelix, 391 Antitragus, 391 Anus, 97, 143, 160 Aorta, origin of, 258

chick, 40

descending, 40, 46, 48, 59, 60, 62, 83, 99, 130, 260, 261

dorsal, 46, 49, 85, 99, 122, 260, 264

pig, 99, 121

ventral, 46, 48, 57, 83, 99, 249, 260 Aortic arches, 59, 60, 121, 122, 263, 264

chick, 57

Aortic arches, human, 83, 261

transformation of, 261 Appendicular skeleton, 315 Appendix epididymidis, 218

testis, 218, 219

vermiformis, 172, 174 Aqueduct, cerebral, 330, 337 Archenteron, 28, 29, 31, 34 Archipallium, 346 Arcuate fibers, 335 Area opaca, 36

pellucida, 36

scrotal, 227

vasculosa, 243 Areolar tissue, 286 Artemia, 14 Arteries, axillary, 268

basilar, 264, 266

brachial, 268

carotid, 99, 121, 262, 263, 266

cerebral, 266

choroidal, anterior, 266

coeliac, 99, 122, 262, 267

development of, 261

epigastric, 266

femoral, 268

gluteal, 268

hepatic, 178

hypogastric, 268

iliac, 123, 267, 268

innominate, 263

intercostal, 266

interosseous, 268

intersegmental, 99, 122, 260, 262, 265

ischiadic, 268

lumbar, 266

mammary, 266

median, 268

mesenteric, 262, 267 inferior, 122 superior, 122, 261

of extremities, 268

of heart, 83

of lower extremity, 268

of pig, 99, 121

of upper extremity, 268

ovarian, 267

peroneal, 268

phrenic, 267

popliteal, 268

puhnonary, 99, 121, 122, 168, 258, 262

radial, 268

renal, 205, 267

sacral, middle, 268

spermatic, 267

spinal, 264

393

394

Arteries, ftapedial, 390

sobdavian, 122, 262, 263, 266, 266

sapnuenal, 267

olDar, 268

umbakal, 86, 99, 123, 135, 260, 267

ventral, 99, 122

ventio-lateial, 99, 122

vertebral, 122,264

viteUine, 46, 58, 63, 86, 99, 122, 260, 261, 262 chick, 42 Artificial parthenog mcs is, 20 Arytenoid cartilage, 166

folds, 117

ridges, 94, 151

swepings, 165 Ascaris megalooephala bivalens, reduction of chromofiomes in spermatogenesb of, 16 univalens, 13 Atrial canal, 251

foramina, 98

septa, 251

valves, 259 Atrio-ventricular bundle, 259

foramen, 252 Atrium, 57, 83, 90, 97, 249, 251 Auditory meatus, external, 90, 112, 146, 191

nerve, 358

ossicles, 389

placode, 45, 48, 385

tube, 82, 161, 389

vesicle, 385 Auricle of ear, 146, 390 Auricular fold, 391 Autonomic system, 366 Axial skeleton, 309 Axillary artery, 268

nerve, 356

vein, 276 Axis cylinder of nerve fiber, 302 Azygos vein, 274

Baby, blue, 255 Back, muscles of, 317 Bars, sternal, 311 Bartholin's glands, 228 Basal pUte, 239, 240, 323, 332 Basilar artery, 264, 266

membrane, 389 Baulic vein, 276, 277 Basophiles, 247 Berlin's renal columns, 202 Bicuspid valves, 121, 259 Bile capillaries, 177

duct, common, 120 Biogenesis, law of, 5 Birds, cleavage of ovum in, 26

gastrulation of, 28

origin of mesoderm in, 31 Bladder, 77, 143, 205, 207 Blastocoele, 24 Blastoderm, 26 Blastodermic vesicle, 26 Blastomeres, 23 Blastopore, 29, 31 Blastula, 24

Blood cells, 42, 243, 244 ichthyoid, 244 sauroid, 244

Blood corposdes, red, 244, 245 white, 245. See also Lemuijit dements, monophyledc theoiy o polyphylectic theory of origin, islands, 38, 42, 243 |Jates,247 sinuses, 281

vascular system, pig, 97, 120 vessds, anomalies of, 277 chan^ at birth, 278 chick. 42, 46, 57 human, 243, 247 pig. 97, 120 primitive, 259 Bhie baby, 255 Body cavities, 179

stalk, 71 Bone, cartilage, 288, 289 growth^, 290 cells, 289 destrojrers, 289 ethmoid, ossification of, 313 formation, endochoodiml, 289 perichondral, 289, 290 periosteal, 289 formers, 288 growth of, 290 histogenesb of, 288 lacrimal, 314 lacuiue, 289 marrow, 289 red, 289 yellow, 290 membrane, 288 of skuU, 314 nasal, 314

occipital, ossification of, 312 palate, 314 regeneration of, 291 sphenoid, ossification of, 313 temporal, ossification of, 313 zygomatic, 314 Border vein, 276 Bowman's capsule, 198, 199 Brachial artery, 268 plexus, 355 vein, 276 Brachium conjunctivum, 337

pontis, 336 Brain, human, 327 of pig, 115 olfactory, 328 vesicles, primary, 322, 327 Branchial arches, 315 chick, 57 human, 82 pig, 89, 94, 112 skeleton. 314 defts, 55, 57

pig, 89 duct, 161 Branchiomerism, 366 Broad ligaments, 221 Bronchi, primary, of pig, 95, 1 19

ventral, 167 Bronchial buds, 119, 167 B runner, duodenal glands of, 173 Bulbar limb, 249 swellings, 121

INDEX

395

Bulbo-urethral glands, 228 Bulbus cordis, 57, 60, 83, 249 Bundle, atrio-ventricular, 259

ground, 325

median longitudinal, 335 Bursa infracardiaca, 190

omental, 189 inferior recess of, 190

pharyngeal, 162

C^UM, 120, 143, 172, 173, 174

Calcar avis, 351

Calcarine fissure, 351

Calyces of metanephros, 120, 199

Canal, atrial, 251

atrio-ventricular, 252

central, of adult spinal cord, 324

entodermal, 159

G&rtner's, 219

Haversian, 290

hyaloid, 381

incisive (of Stenson), 148

inguinal, 221, 222

lacrimal, 384

pleuro-peritoneal, 183

Stenson's, 148 CanalicuU, 289

aberrans, 199 Capillaries, bile, 177 Capsule, Bowman's, 198, 199

cells, 306

internal, 345

of liver, 192

periotic, 312

vascular, of lens, 378, 381 Cardiac diverticulum, 119

glands, 170

muscle, 291, 293 Cardinal veins, 123

anterior, 49, 58, 59, 60, 101, 261, 268, 271 common, 58, 60, 97, 101, 261, 268, 271 posterior, 58, 62, 63, 102, 261, 268, 274 Carotid arteries, 99, 121 common, 263 internal, 262, 263, 266

gland, 369 Carpus, ossification of, 316 Cartilage, arytenoid, 166

bone, 288, 289 growth of, 290

comiculate, 166

cricoid, 166

cuneiform, 166

elastic, 287

fibro-, 287

histogenesis of, 287

hyaline, 287

Meckel's, 315

of larynx, 165

Reichert's, 390

thyreoid, 166, 315 Cauda equina, 326 Caudate lobe of liver, 192

nucleus, 345 Caul, 74, 242 Cavity, body, 179

head, v^66

joint, 291

Cavity, marrow, 290

medullary, 290

oral, 142

pericardial, 53, 179, 180

peritoneal, 53, 185

pleural, 53, 183, 185

pleuro-pericardial, 40

pleuro-peritoneal, 179

tympanic, 161, 389 Cell-chain theory of development of ner\'e fibers,

306 Cells, aggregation, 3

blood, 42, 243, 244 ichthyoid, 244 sauroid, 244

bone, 289

capsule, 306

chromaffin, 368, 369

cone, of retina, 382

decidual, 236

division of, 12

enamel, 156

ependymal, 302, 307, 324

ethmoidal, 313, 376

follicle, 8

ganglion, 305 unipolar, 305

genital, 213

germ, 7, 302

giant, 247

gland, 297

goblet, 283

hair, 295, 296, 387

interstitial, of testis, 213

mass, inner, 71 intermediate, 52

mastoid, 314

migration, 3

multiplication, 3

muscle, smooth, 291

nerve, 300

neuroglia, 300, 302, 307, 308

rod, of retina, 382

sense, 387

sex, 208

sheath (of axis cylinder), 306

sperm, 10

supporting, 371, 387 of neural tube, 307 of spinal ganglia, 305, 306

sustentacular (of Sertoli), 14, 213

taste, 371 Cement of teeth, 157 Centra of vertebras, 142 Central canal of adult spinal cord, 324

nervous system, 321 chick, 44, 55 human, 80, 321 pig, 114

sulcus, 351 Centrosome, 7 Cephalic flexure, 55, 79, 327

pig, 89 vein, 276, 277 Cerebellum, 115, 336 Cerebral aqueduct, 115, 330, 337 artery, anterior, 266 middle, 266 posterior, 266

396

Cerebral corlex, 351

Cle«v4ge of ovum, reptile*, 26

Cleft palule. 149

nerves, 115,357

slemum, 316

veins. 273

xiphoid process, 316

Cervical duct, 161

Clitoris, 143. 223

Cloaca. KJ, 97, 171,205

fleiure. 328

anomaly of, 208

gabion, 368

Cloacal membrane. 83, 160, 205

tubercle, 225

SLtth, 116

Closing plates. 57. 60, 95, 118, 160

sinus, 112

ritw. 239

pig, 90

Coccygeal gland. 2H2

veTicie. 161

Cochlenrdurl. 384,386

Chamber, anlerior. of eye, 377. 3S3

Cceliacarlen,*), 122,262,267

Chick embryos, 36. 43, 55

aiU. primitive, 267

of fifty hours' incubation, 55

Ccelom, 29, 33, 180

of twenty houis' duration, 36

chick, 40, 53

human. 179

preservation of. .W

pleural, 96

study of. 36, «, 55

Ccelomic pouches. 29

Chin, 145

Colic valve, 174

ChOMK. 147

Collateral eminence, 351

primiUve. 373

fissure, 351

■econdaiy, 374

Colliculus. facial, 364

Chondrification of skull, 312

inferior, 337

of vertebrtE, 310

Chondrioconta. 2S5

superior, 337 Coloboma.379

Chondrocranium.312

ossification of, 3ll

Colon. 120,174

Chorda dorsalis, 309

Column, gray. 324

origin of, 35

Columns, muscle. 293

gubernaculi. 221,222

renal, 202

Chordmie tendinea:, 2SP

++++Chorioid fissure of eye, 376. 379

jrray, m

layer of eve. 3S.1

bipiHicampal, .W

plexus, 141. 142,334.338,342

of telencephalon, .W,.

Chorioidal arter>-, anterior, 266

posterior, of labia majoi*. 225

fissure. 342. 349

white. 325

Chorion. oriKin of, 65

Compact byer, 236, 240

chick. 65

Concealed tesds, 224

frondosum, 235, 237

Conchar. 146.313,376

human. 72

Concrescence, theory of, 31

Iseve. 235. 237

Cone cells of retina, 382

pis, (», 70

Conjunctiva. 383

villi of. 71,72.232,237

Connective tissue, 285

Chromaffin bodies, 368

while fibrous. 285

aortic, 3W

Copula, 94, 117.150

Coracoid process, 316

accessorjV 1 7, 32

Cord, genital, 210

number of. 13

medullary. 217

Cilia, 383

nephrogenic 197,201

Ciliary bodies. 383

spermatic, 224

Ranglion. 361,368

spinal, 322

muscle, 383

testis, 212, 213

Circulation. feUl, 277

umhilical, human, 70

portal, 279

of pig. 70

vitelline, 46

Corium, 295 . . , ,„

Circulatory system, 83

Osteraa chyU, 279

Corneal tissue, 286

Clava, 336

Corniculalc carlilagcs, 166

Clavicle, ossification of, 315

Corona mdiata, 9

Cleevajjeofovum, 23

Coronarj- appendagcE, 192

ligament. 192

sinus. 253, 271

birds, 26

sulcus, 225. 2S1

frog, 25, 26

Corpus albicans, 217

primates, 27

cilosum, 346, 348

INDEX

397

Corpus hemorrhagicum, 217

luteum, 217 spurium, 217 verum, 217

striatum, 329, 341, 345 Corpuscles, blood, red, 244, 245

white, 245. See also Leucocytes.

lamellated, 371

renal, 133, 198, 199

splenic, 282

tactile, 371

thymic, 163 Cortex, cerebral, 351

of cerebral hemispheres, 329

of metanephros, 202

primitive, of cerebral hemisphere, 341 Corti*s organ, 359, 386

pillars, 387 Costal processes, 310 Costo-cervical trunk, 266 Cotyledons of human placenta, 240 Cowper's glands, 228 Crest, ganglion, 304, 353

neural, 304 Cribriform plates, 313 Cricoid cartilage, 166 Crista ampullaris, 386

galli, 313

inguinalis, 221

terminalis, 254 Crura cerebri, 330 Cms longum, 390 Cryptorchism, 214, 224 Cumulus oophorus, 216 Cuneiform cartilages, 166 Cuneus, 336, 351 Cutis plate. 111 Cuvner's ducts, 58 Cyclopia, 352 Cystic duct, 120, 177

kidney, 205 Cysts, dermoid, 295 Cytoplasm of ovum, 7

Darwin's tubercle, 391

Decidua basalis (serotina), 232, 236, 237, 239

capsularis (reflexa), 231, 236

vera (parietalis), 232, 235 Decidual cells, 236

membranes, 230, 231 separation of, 241

teeth, periods of eruption, 157 Dendrites, 304 Dental canaliculi, 157

lamina, 153

papilla, 153, 157

pulp, 157

sac, 157 Dentate nucleus, 337 Dentinal fibers of Tomes, 157 Dentine, 157 Derma, 295 Dermatome, 293 Dermoid cysts, 295 Dermo-muscular plates, 51 Dcrmo-myotome, 285, 293 DescendinR tract of fifth nerve, 335, 361 Determination of sex, 22

Diaphragm, 187, 188

anlage of, 61

anomalies of, 194 Diaphra^atic hernia, 194 Diaphysis, 290 Diaster, 13

Diencephalon, 56, 80, 92, 115, 327, 338 Differentiation of embryo, 3

of tissues, 4 Digestive canal, chick, 45, 57 human, 80 pig, 6 mm., 93

glands, human, 81 Dilator muscles of iris, 383 Discs, intercalated, 293

inter\'ertebral, 310 Dissecting instruments, 137 Dissections, lateral, of viscera, 138

median sagittal, 140

pig embryos, 137

ventral, 143 Diverticulum, cardiac, 119

hepatic, 96, 119, 175

Meckel's, 79, 171

of ileum, 171

of Nuck, 224

of pharyngeal pouches, 95 Ducts, branchial, 161

cervical, 161

cochlear, 384, 386

common bile, 120

Cuvier's, 58

cystic, 120, 177

Ebner's, 152

genital, 208, 210, 218

hepatic, 120, 177

mesonephric, 120, 199, 210

milk, 298

Mullerian, 210

naso-lacrimal, 384

pancreatic, 179

papillary, 201

para-urethral, 227

periportal, 177

pronephric (primary excretory), 196, 199

thoracic, 279

thyreoglossal, 164

vitelline, 159 Ductuli efferentes, 199, 218 Ductus arteriosus, 263, 279

choledochus, 120, 177

deferens, 218

endolymphaticus, 385

epididymidis, 218

reuniens, 386

venosus, 101, 124, 270, 279 Duodenal glands (of 6 runner), 173 Duodeno-hepatic ligament, 192 Duodenum, 119, 170, 173 Dyads, 16

E\R, 384

auricle of, 146

external. 112. 146, 384, 390

inner, v^84, 385

internal, 45

middle, 3H4, .^89 Kbner's ducts and glands, 152

398

INDEX

Ectocknn, 3, 28

fonnatlon of, 28 Ectodennal denx-adves, histogenesb ci, 294 Ectoplasm, 285

Efferent ductules of epididyinis, 199 Elastic cartilage, 287

tissue^ 286 Eleidiii,294

Ellipoids of ^leen, 282 Embryos, duoc, 36, 43, 55

of thirty-dght hours' duration, 43 of twenty hours' duration, 36 of twenty-6ve hours' duration, 38 preservation of, 36 study of, 36 human, 71 crown-rump length, 87 estimated age. 87 ofCo6te,78 of Dandy, 76 of Etemod, 77 of His, 2^ mm., 78 4.2mni^79 Normentafel, 84, 85 of Krdmer, 76 of MaU, 76 of Peter, 74 of Spee, 74 of Thompson, 76 pig, 6 mm., 89

10 mm., transi'erse sections, 125 10 to 12 mm., 112 dissection of, 137 trans\'erse sections of 6 mm., 104 whole, for study, 137 Eminence, collateral, 351 Enamel celb, 156 layer, 156 organs, 153 pulp, 155 Encephalon, 80

Endocardial cushions, 98, 121, 131, 251, 252 Endocardium, 131, 249

chick, 41 Endochondral bone formation, 289 Endolymphatic sac, 385 Endoplasm, 285 ?2ndotheIium, 54 Enlargement, cervical, 326

lumbar, 326 Entoderm, 3, 28, 29

formation of, 28 Entodermal canal, 159 epithelium, 170 histogenesis of, 283 Eosinophiles, 246 Ependymal celb, 302, 307, 324 layer, 59, 126, 307, 322, 333 zone, 301 Epicardium, 42, 98, 131, 249 Epidermis, 294

anomalies of, 295 Epididymis, 219

efferent ductules of, 199 Epigastric arteries, 266 Epigenesis, 2

Epiglottis, 94, 116, 143, 151, 165 Epiphysis (pineal gland), 141, 290, 310, 330, 339 Epiploic foramen (of Winslow), 134, 190

Epistropheus, 310 Epithalamus, 330 Epithdia, 3

Epithelial bodies, 82, 163 Epithelium, 54

basal, of cochlear duct, 387

entodennal, 170 histogenesis of, 283

olfactory, 128

respiratory, 168

stratified, 294 Epitrichium, 294, 295, 296 Eponychium, 299 Epoophoron, 199, 219 Erythroblasts, 244, 245 Erythroc>'tes, 244, 245 Erythroplastids, 245 Esophagus, 81, 94, 95, 119, 143, 169 Ethmoid bone, ossification of, 313 Ethmoidal cells, 313, 376 Ethmo-turbinals, 376 Eustachian tube, 161, 389

valve, 254 Excretory duct, primary, 62, 196, 199 Expression, muscles of, 320 Elxtra-embryonic mesoderm, 71 Extremities, arteries of, 26S

muscles of, 318

veins of, 276 Eye, chick, 43, 45, 47, 59

human, 80, 376

pig. 89 Eyelashes, 383 Eyelids, 383

Fach, de\*elopment of, 144 Facial colliculus, 364

ner\'e, 92, 116,362,363 Falciform ligament, 133, 180, 192 False hermaphroditism, 228 Fasciculi proprii, 325 Fasciculus cuneatus, 325

gracilis, 325 Femoral artery, 268

nerve, 356

vein, 277 Femur, ossification of, 316 Fertilization, 19, 20

significance of, 21 Fertilizin, 20 Fetal circulation, 277

membranes, human, 71 pig, 68 Fetus, 87

relation of, to placenta, 241 Fibrils, horn, 299 Fibro-cartilage, 287 Fibula, ossification of, 316 Filament, axial, of spermatozoon, 11

spiral, of spermatozoon, 1 1

terminal, of spermatozoon, 11 Filiform papillse, 151 Filum terminale, 326 Fingers, supemumeran*, 316 Fissure, calcarine, 351

chorioidal, 342, 349, 376. 379

collateral, 351

great longitudinal, 342

INDEX

399

Fissure, hippocampal, 346, 349

lateral, 349

of Rolando, 351

parieto-occipital, 351

Sylvian, 349

ventral median, 325 Fixation of pig embryos, 137 Flagellum of spermatozoon, 11 Flexure, cephalic, 55, 79, 327

cervical, 328 pig, 89

iliac, 174

pontine, 327 Flocculus, 337 Floor plate, 322, 324, 332 l*oliate i>apilke, 152 Follicle cells, 8 roUicles, Graafian, 9, 215

primordial, 215

vesicular, 215 Fontanelles, 314 Foramen, atrio-ventricular, 98

caecum, 151, 164

epiploic (of Winslow), 134, 190

interatrial, 98, 253

interventricular, 115, 258, 329, 343 closure of, 259

mandibular, 315

Monro's, 343

of Winslow, 134, 190

ovale, 98, 120, 253, 254, 255 section through, 130 Fore-brain, chick, 40, 43, 44, 47, 59

human, 327 Fore-gut, chick, 39, 40, 41, 49, 57

human, 81,159, 160

pig, 93 Fore-skin, 226 Fomices of vagina, 220 Fornix, 346, 347 Fossa, incisive, 148

olfactory, 371,372

ovalis, 255

supratonsillar, 161

tonsilla , i61 Fovea cardiaca, 39, 40, 41, 83

chick, 49 Frenulum prepucii, 226 Frog, cleavage of ovum in, 25, 26 Frontal operculum, 349

sinus, 376 Fronto-nasal process, 372 Fronto-parietal operculum, 349 Froriep's ganglion, 93, 116, 360 Fundus of uterus, 220 Fungiform papills, 151 Funiculi of spinal cord, 325 Furcula of His, 165

Gall bladder, 120, 177 Ganglion, 353

accessory, 364

cell layer, 382 of retina, 358

cells, ms

unipolar, 305 cervical, 368 ciliary, 361 , 368

Ganglion crest, 304, 353 Froriep's, 93, 116,360 geniculate, 92, 116, 363 habenuls, 338 .jugular, 93, 116 nodose, 93, 116, 364 otic, 368

petrosal, 93, 116,364 prevertebral, 368

root, 93, 364

semilunar, 92, 116, 361

sphenopalatine, 368

spinal, 50, 1 16, 304 supporting cells, 305, 306

spiral, 358, 359

submaxillary, 368

superior, 93, 116, 364

sympathetic, 305, 367

trunk, 364

vestibular, 358

vagus accessory, 116

visceral, 368 Gartner's canals, 219 Gastric glands, 1 70 Gastro-hepatic ligament, 192 Gastro-lienic ligament, 191 Gastrula, 28 Gastrulation, 28

of amphibia, 28

of Amphioxus, 28

of birds, 28

of mammals, 29

of reptiles, 28 Geniculate bodies, 330

ganglion, 92, 116, 363 Genital cells, 213

cord, 210

ducts, 208, 210, 218

eminence, 114, 225

fold, 97, 120, 143, 197, 208

glands, 97, 143, 208 and mesonephric tubules, union of, 218

swellings, 225

tubercle, 225 Genitalia, external, 224

internal, ligaments of, 221 Germ cells, 7, 302

layers, 2, 3 derivatives of, 54 origin of, 23

plasm, continuity of, 4 Germinal disc, 26 Giant cells, 247 Gill slits, 55 Glands, accessory genital, 227

alveolo-lingual, 152

Bartholin's, 228

Brunner's, 173

bulbo-urethral« 228

cardiac, 170

carotid, 369

cells, 297

coccygeal, 282

Cowper's, 228

duodenal (of Brunner), 173

Ebncr's, 152

gastric, 170

genital, 97, 143, 208 and mesonephric tubules, union of, 218

400

INDEX

Glands, hemolymph, 281

intestinal, 1/3

lacrimal, 383 accessory, 384

lymph, 281

mammary, 1 14, 297 rudimentary, 298 supernumerary, 298

Meibomian, 383

parathyreoid, 118, 163

parotid, 152

pineal, 141, 290, 310, 330, 339

prostate, 227

salivary, 152

sebaceous, 296

sublingual, 152

submaxillary, 152

sudoriparous, 297

suprarenal, 143, 368, 369

sweat, 297

tarsal, 383

thymus, 118

thyreoid, 118, 164

urogenital, 144

uterine, of pregnancy, 236

vestibular, 228 Glans clitoridis, 225

penis, 226 Glomerulus, 133, 195, 198 Glomus caroticum, 369

coccygeum, 282 Glossopharyngeal nerv^e, 93, 116, 362, 364 Glottis, 94, 117, 151 Gluteal artery, 268

vein, 277 Goblet cells, 283 Gonads, 83

Graafian follicle, 9, 215 Granular layer of cerebellum, 337

leucocytes, 246 Granules, pigment, 295 Gray column, 324

commissures, 325

rami, 367 Groove, laryngo-tracheal, 164

neural, 300

primitive, 31

rhombic, 334

urethral, 225 Ground bundles, 325 Growth of embryo, 3 Gubernaculum testis, 222, 223 Gyrus dentatus, 346

hippocampi, 346

HiKMOPOiESis, 243 Hair, 295

bulb, 296

cells, 295, 296, 387

papilla, 296

shaft of, 296

sheath, 296 Hare lip, 146 Haversian canal, 290 Head cavities, 366

fold, 39

muscles of, 319

process, 32, 33^ 37, 38

Head, vertebrate, segmentation of, 365 Heart, chick, 41,46,49 descent of, 259 human, 83, 247, 248 pig, 90, 97, 116,120,143 primitive, chick, 42 ventricle of, 57 Helix, 391

hyoid, 391 Hemiazygos vein, 274 Hemispheres, cerebral, 328, 329, 349 Hemolymph glands, 281 Henle*s loop, 203 Hensen*s knot, 31, 36, 51 Hepatic artery, 178 diverticulum, 96, 119, 175 duct, 120, 177 vein, 270 common, 98 Heredity, Mendel's law of, 21 Hermaphroditism, 228

false, 228 Hernia, diaphragmatic, 194 inguinal, 224 umbilical, 70 Hind-brain, chick, 41, 44, 48, 59

human, 80, 327 Hind-gut, 57, 64, 83, 93. 159, 160 Hippocampal commissure, 347

fissure, 346, 349 Hippocampus, 346, 349

minor, 351 His, furcula of, 165 Histogenesis, 283 defined, 4 of bone, 288 of cartilage, 287 of ectodermal derivatives, 294 of entodermal epithelium. 283 of mesodermal tissues, 284 of muscle, 291 of ner\'ous tissue, 300 Historical. 1 Horn fibrils, 299 gray, 324

greater, of hyoid bone, 315 lesser, of hyoid bone, 315 Horse-shoe kidney, 205 Howship's lacunae, 289 Human embryos

, 71

crown-rump length, 87 estimated age, 87 of Coste, 78 of Dandy, 76 of Eternod, 77 of His, 2.5 mm., 78 4.2 mm., 79 Normentafel, 84, 85 of Kromer, 76 of Mall, 76 of Peter. 74 of Spee, 74 of Thompson, 76 Humerus, ossification of, 316 Hyaline cartilage, 287 Hyaloid canal, 381 Hvdramnios, 74 H>Tnen, 219, 221 Hyoid arch, 90

Hyoid helii, 391 Hyonijuidibular def[, 90 Hypogastric artery, 268 Hypoglossal nene. W. 116, 151, 360

Hypophysis, 57, Sf. 339

anterior lolje of, 59

posterior iobe of, 1 15 Hypospadias, 227 Hypoihalamus, 3,10

diverticulum of, 171 Hiac artcrici!. 123, 267, 268 flexure, 174 veins, 274, 275 Ilium, ossification of. 316 lni]jlantation of nvum. 231 Incisive canals (of Stenson), 148

fossa, 143 Incus, 315, 389, 390 Infundibulum, 330, 339 Inguinal canal, 22t, 222 fold, 220. 221 hernia. 224 Inner cell mass, 71

epithelial mass of gonad, 208 Innominate artery. 263 Instruments, dissecting, 137 Insula, .M9

Interatrial foramen, 98, 252 Intercalated discs, 193 Intercostal arteries. 266 Intermediate cell mass. W, 52 Interosseous artery, 268

Jntersegmenta! arteries, 99, 1 22, 260, 262, 265 fiber tracts, 335 veins, 274 Interstitial cells of testis, 213 Interi'enlricular foramen, 1 15, 258, 329, 343 closure of, 259 septum, 121.258

sulcus

258

Intervertebral discs, 310

muscles. 317 Intestinal glands, 173

loop, 143, 170 Intestine, human, 81, 83, 160, 170

pig. 96. 120

villi of, 173 Introduction, 1 Iris, 382. 3&)

muscles of, 383 Ischiadioc vein, 274

artery, 268 Ischium, ossification of, 316 IsUndof Keil..H9 Islands, blood, 243

of pancreas, 179 Isolecilhal ova, 23 Isthmus. 115.328,330

Jacobson's organ. 357, 374 Jomt cavity, 291

}oinls, 291 ugular ganglion, 93, 116 s»cs, 279 veins, 123, 2T3

Keratin, 299 Keratohyalin, 294 Kidney, anomalies of, 205

calyces of, 120

cystic, 205

horse-shoe, 205

human, 199

tubules of, 120. 20t. 203 Knot, primitive (of Hensen), 36, 51

Labia majora, 225

minora, 225, 227 Labyrinth, membranous, 45 Lacrimal bone, 314 canab. 384

glands, 38.) accessory, 384

groove, M Lacuna;, bone, 289

Hoviship's. 289 Lame! lie, periosteal. 290 Lamella led corpusclesj 371 Lamina perpend iculans, 31

terminal is, 329, .142, 346 Langhans' layer, 238 Larjngeal nerves, recurrent. 264 Laryngo- tracheal gtoove, 164 Larj-nx, Ifrl, 165

cartilage of. UiS

musrlesof .?30

ventricles of, 165 Law, Mendel's, of heredity, 21

of biogenesis, 5

epcndymal, 126, 307, 322, 333 epitrichial, 296

.-,■11, ,182

313

++++I 23

Sranului, ,U; Langhans', 2.18 mantle, 126,322,324 marginal, 126.322,325 medullary, 33" molecular. 337

e fit,,-!

ofri

i, 126

pigment, of retina, 126, 377, 381 retinal, 377, 381 sclerotic, of eye, 383 spongy. 236, 240 Lecithin, 7 Lemniscus. 338 median, ,135 Lens of eye, chick, 45, 47 human, 376 fibers of, 379

pupillary membrane of, 381 suspensoo' ligament of, 381 vascular capsule of, 378, 381 pig. 89 pit. 376 plate. 376 vesicles, 59. 376, 379

402

INDEX

Lens-stars, 380 Lenticular nuclei, 345 Lesser i)eritoneal sac, 133, 189 Leucocytes, 245

granular, 246

mast, 247

mononuclear, large, 246

non-granular, 245

polymorphonuclear, 246 Ligament, broad, 221

coronary, 192

duodeno-hepatic, 192

falciform, 133, 180, 192

gastro-hepatic, 192

gastro-lienic, 191

lieno-renal, 191

of internal genitalia, 221

of liver, 191

of testis, 221

proper, of ovar>', 221

round, 220, 222

spheno-mandibular, 315

stylo-hyoid, 315

susfKinsory, of lens, 381 Ligamentum arteriosum, 279

labiale, 222

ovarii, 210

scroti, 222

teres, 271, 279

testis, 210, 222

umbilicale medium, 208

venosum, 270, 279 Limbus ovalis, 254 Limiting membranes of retina, 382 Line, milk, 298 Linguo- facial vein, 101 Lip, 373

hare, 146

rhombic, 334 Liver, anlage of, 57, 62, 175

anomalies of, 178

caudate lobe of, 192

cords, 131

human, 81, 175

ligaments of, 191

lobules of, 178

pig, 90, 93, 96, 1 19

quadrate lobe of, 192

sinusoids of, 57, 62, 176 Lobes of cerebrum, 349 Lobule of ear, 391 Lobules of liver, 1 78 Lobuli epididymidis, 218 Lumbar arteries, 266

enlargement, 326

veins, 276 Lumbo-sacral plexus, 356 Lung buds, 82 Lungs, human, 81, 164, 167 apical buds, 167 changes at birth, 168 stem buds, 167

pig, 95, 119 Lunula, 299 Lymph glands, 281

sacs, 279, 280 Lymphatic system, 279 Lymphatics, origin of, 279

peripheral, 279

Lymphocytes, small, 245 Lymphoid tissue of spleen, 282

Maculae acustioe, 386 Magma reticulare, 71 Mall's pulmonary ridge, 183 Malleus, 315, 389

muscles of, 390 Mammals, cleavage of ovum in, 26

gastrulation of, 29

origin of mesoderm in, 32 Mammary arteries, 266

glands, 114, 297 nidimentar>', 298 supernumerary, 298 Mammillarj' bodies, 330, 347

recess, 330, 341 Mandibular arch, 90

foramen, 315

nerve, 116, 361

process, 79, 80, 90, 112, 314, 372 Mantle layer, 126, 322, 324 Manubrium, 311 Marginal layer, 126, 322, 325

sinus, 241

zone, 302 Margo thalamicus, 327 Marrow, bone, 289 red, 289 yellow, 290

cavity, 290 Massa intermedia, 341 Mast leucocytes, 247 Mastication, muscles of, 319 Mastoid cells, 314

process, 314 Maturation, 12, 14

of mouse ovum, 18

significance of, 21 Maxilla?, 315 Maxillary nerve, 116, 361

process, 79, 80, 90, 112, 314, 372

sinus, 376 Maxillo-turbinal anlage, 376 Meatus, external auditory, 90, 112, 1^

inferior nasal, 376 Meckel's cartilage, 315

diverticulum, 79, 171 Meconium, 175 Median arter>', 268

longitudinal bundle, 335

nerve, 356 Mediastinum, 167

of ovary, 214

testis, 213 Medulla oblongata, 80, 330 Medullary cavity, 290

cords, 217

layer, 337

sheath, 306

velum, 330, 337 Mcgakatyocytes, 247 Meibomian glands, 383 Membrana tectoria, 387 Membrane, anal, 160, 205

basilar. 389

bone, 288

bones of skull, 314

INDEX

403

Membrane, cloacal, 160, 205

decidual, 230, 231 separation of, at birth, 241 tjrmpanic, 117

limiting, of retina, 382

obturator, 316

pericardial, 187

pharyngeal, 159

pleuro-pericardial, 182, 183

pleuro-peritoneal, 182, 183

pupillary, 381

Reissner's, 389

synovial, 291

tympanic, 391

urogenital, 160, 205

vestibular, 389

vitelline, 7 Membranous labyrinth, 45 MendePs Law of heredity, 21 Menstruation, 10, 230

uterus during, 230 Mesamceboids, 243, 244 Mesencephalon, 80

chick, 44, 48, 60

human, 330, 327, 337

pig, 92, 115 Mesenchyma, 3

chick, 41, 53

human, 284 Mesenteric arteries, 262, 267 inferior, 122 superior, 261

veins, 270 superior, 99, 100, 122, 125 Mesentery, 93, 96, 120, 133, 179, 180, 191, 192

anomalies of, 194

dorsal, 81, 192 Mesocardium, 180

dorsal, 49, 249 Mesocolon, 180, 193, 194 Mesoderm, 3, 28

amphibian, 30

Amphioxus, 29

birds, 31

extra-embryonic, 34, 71

intra-embryonic, 34

mammal, 32

origin of, 29

primary, 28

reptiles, 30

somatic, 52, 53, 69

splanchnic, 53, 69, 169, 366

Tarsius, 34 Mesodermal segments, 2, 40, 51, 62, 64

tissues, histogenesis of, 284 Mesoduodenum, 180, 193 Mesogastrium, 180 Mesonephric duct, 49, 52, 62, 97, 120, 199, 210

fold. 197

tubules, 197 and genital glands, union of, 218 Mesonephros, 52, 83, 90, 93, 97, 120, 143, 195, 197 Mesorchium, 210 Mesorectum, 180, 194 Mesothelium, 54, 284

peritoneal, 170 Mesovarium, 210 Metameres, 2 Metamerism, 2

Metanephros, 52, 97, 120, 143, 195, 199

and umbilical arteries, section through, 136

calyces of, 199

collecting tubules, 199, 201

cortex, 202

pelvis, 199

tubules, 199, 201

ureter, 199 Metaphase of mitosis, 13 Metatarsus, ossification of, 316 Metathalamus, 330

Metencephalon, 80, 92, 115, 327, 328, 336 Methods of study, 5 Mid-brain, 80, 327

chick, 43, 44, 47 Mid-gut, 57, 159 Migration, cell, 3 Milk ducts, 298

line, 114,298

teeth, periods of eruption, 157 Minot's ichthyoid blood cells, 244 Mitosis, 12

phases of, 12-14

significance of, 21 Mitotic figure, 13 Mitral valve, 259 Moderator muscles, 259 Modiolus, 389 Molecular layer, 337 Monaster, 13

Mononuclear leucocytes, large, 246 Monophyletic theory of origin of blood elements,

243 Monro's foramen, 343 Mons pubis, 233

Montgomery's rudimentary mammary glands, 298 Morula, 24

Motor nerves, somatic, 360 Mouse ovum, fertilization of, 19

maturation of, 18 Mouth, pig, 6 mm., 93 Miiller's fibers, 382

tubercle, 221 Miillerian ducts, 210 Multiplication, cell, 3 Muscles, 316

anomalies of, 320

cardiac, 291, 293

ciliary, 383

columns, 293

dilator, of iris, 383

histogenesis of, 291

inter\'ertebral, 317

moderator, 259

of back, 317

of expression, 320

of extremities, 318

of head, 319

of larynx, 320

of maJIeus, 390

of mastication, 319

of neck, 317

of pharynx, 320

of tongue, 320

of trunk, 317

papillary, 259

plate, 60, 62

skeletal, 291, 292

smooth, 291

404

INDEX

Muscles, sphincter, of iris, 383

stapedial, 390

stemo-cleido-mastoid, 364

thoraco-abdominal, 317

trapezius, 364

voluntary, 52 Muscular system, 316 Musculocutaneous nerve, 356 Myelencephalon, 80, 92, 115, 328, 330, 332 Myelin, 306

development of, 326

sheath, 306 Myelocytes, 245, 246 Myoblasts, 292, 293 Myocardium, 42, 98, 249, 259 Myofibrillae, 293 Myotomes, 2, 292

changes in, during formation of adult muscles, 317

chick, 51

Nail fold, 298, 299

human, 298 Naris, external, 373 Nasal bone, 314

meatus, inferior, 376

passages, 374

processes, 145, 372, 373

septum, 313, 373 Naso-lacrimal duct, 384 Naso-turbinal anlagc, 376 Navel, 70

Neck, muscles of, 317 Neopallium, 346 Nephrogenic cords, 197, 201

tissue, 120, 136,202 Nephrostome, 195 Nephrotome, 195

chick, 40, 52, 64 Nerve, abducens, 116, 361

accessorius, 116

acoustic, 92, 1 16, 358

auditory, 358

axillarv, 356

cells, 300

cerebral, 115, 357

facial, 92, 116,362,363

femoral, 356

fibers, 300 cell-chain theory of development, 306 layer, 382

glossopharyngeal, 93, 116, 362, 364

hypoglossal, 93, 116, 151, 360

mandibular, 116, 361

maxillary, 116, 361

median, 356

motor somatic, 360

musculocutaneous, 356

obturator, 356

oculomotor, 92, 115, 330, 360

olfactory. 357

ophthalmic, 116, 361

optic, 115,358,383

peroneal, 356

petrosal, superficial, 116, 363

phrenic, 355

radial, 356

recurrent laryngeal, 264

Nerve, sciatic, 356

sensory, somatic, 357

somatic, motor, 360 sensory, 357

spinal, 116, 353 accessory, 93, 116, 364 efferent or ventral root fibers of, 302

terminal, 358

tibial, 356

trigeminal, 92, 116, 361

trochlear, 116,330,361

ulna, 356

vagus, 93, 1 16, 362, 364

visceral mixed, 361 Nervous layer of retina, 126

system, 91, 114 central, 321 chick, 44, 55 human, 80, 321 peripheral, 353 sympathetic, 366

tissue, histogenesis of, 300 Neural crest, 50, 93, 304 chick, 41

folds, 38, 40

groove, 3S, 300

plate, 300

tube, 38, 40, 64, 300, 332 anomalies of, 352 origin of, 29, 30 supporting cells of, 307 Neurenteric canal, 31, 32, 33, 76 Neurilemma, 306 Neuroblasts, vS02

differentiation of, into neurones, 302

of retina, 382 Neurofibrillar, 304 Neuroglia cells, 300, 302, 307, 308

fibers, 300, 302, 307, 308 Neurokeratin, 306, 308 Neuromeres, 44, 104, 115, 334 Neurones, 302

afferent, 305

differentiation of neuroblasts into, 302

theory, 305 Neuroporcs, 40, 321

anterior, 43 Ncutrophiles, 246 Nipple, 298 Node, primitive (of Hensen), 51

of Ranvier, 306 Nodose ganglion, 116 Nodulus cerebclli, 337 Normoblasts, 244 Nose, 371 Notochord, 33, 38, 309

chick, 40, 64

origin of, 29, 35 Notochordal canal, 33

plate, 31,32, 37, 38 Nuclear zone, 302 Nuclei pulposi, 35, 309 Nucleolus, 7 Nucleus ambiguus, 364

caudate, 345

cuneatus, 335

dentate, 337

gracilis, 335

lenticular, 345

INDEX

40s

Nucleus of pons, 536

olivary, 335

receptive, 335

red, 337

ruber, 337

terminal, 335 Nuck's diverticula, 224 Nymphae, 227

Obex, 334

Obturator membrane, 316

nerve, 356 Occipital bone, ossification of, 312 Oculomotor nerve, 92, 115, 330, 360 Odontoblasts, 157 Olfactory apparatus, 346

brain, 328

epithelium, 128

fossa, 371, 372

lobe, 346

nerve, 357

organ, 371

pits, 112,371,372 pig. 89

placodes, 371

stalk, 346

tracts, 346 Olivary nucleus, 335 Omental bursa, 189

inferior recess of, 190 Omentum, 133, 169, 180, 191, 192 OScyte, 18

primary, 18 Oogenesis, 8 Oogonia, 18 Operculum, 349 Ophthalmic nerve, 116, 361

vein, 273 Optic chiasma, 329, 358

cup, 56, 112,328,376,381

nerve, 115,358,382

placode, 376

recess, 330, 343

stalks, 47, 59, 376

tract, 358

vesicles, 40. 43, 47, 59, 343 Ora serrata, 381 Oral cavity, 142 Orbital operculum, 349 Organ, Corti's, 359, 386

Jacobson's, 357, 374

spiral, 386, 387

vomero-nasal, 357, 374 Os coxa*, 316 Ossicles, auditory, 389 Ossification of carj^us, 316

of chondrocranium, 312

of ethmoid bone, 313

of femur, 316

of fibula, 316

of humerus, 316

of ilium, 316

of ischium, 316

of metatarsus, 316

of KKcipital bone, 312

of patella, 316

of phalanges, 316

of pisiform, 316

Ossification of pubis, 316

of radius, 316

of skull, 312

of sphenoid bone, 313

of tarsus, 316

of temporal bone, 313

of tibia, 316

of ulna, 316

of vertebrae, 310 Osteoblasts, 288, 289 Osteoclasts, 289 Ostium abdominale, 210

vaginae, 221 Otic ganglia, 368

vesicle, 45 Otocyst, 45, 56, 60, 80, 92, 385 Ovarian arteries, 267

pregnancy, 20

vein, 275 Ovary, 214

anomalies, 218

compared with testis, 217

descent of, 222

mediastinum, 214

prop)er ligament of, 221

septula, 214

stroma of, 215 Ovulation, 10 Ovum, cleavage of, 23. See also Cleavage of ovum,

human, 7

fertilization of, 20

implantation of, 231

isolecithal, 23

maturation of, 17, 18

mouse, fertilization of, 19

segmentation of, 23. See also Cleavage of ovum.

structure of, amphibian, 7 bird, 7 monkey, 10

telolecithal, 23

Palvte bones, 314

cleft, 149

development of, 146

premaxillary, 373

primitive, 373

soft, 149 Palatine processes, lateral, 147

tonsil, 82, 118, 162 Pallium of cerebral hemispheres, 329

of cerebrum, 341 Pancreas, alveoli of, 179

human, 81, 178 accessor>' duct of, 179

islands of, 1 79

pig, 96, 120 Pancreatic duct, 179 Papilla-, dental, 153, 157

hair, 2%

of tongue, 151, 152

renal, 202 Papillary ducts, 201

muscles. 259 Paradidymis, IW. 218 Parathyreoid gland, 82^, 118, 163 Paraurethral ducts, 227 Parietal pleura, 168 Parietals, 314

4o6

INDEX

Parieto-occipital fissure, 351 Parolfactory area, 346 Paroophoron, 199, 219 Parotid glands, 152 Pars oeca, 381

ciliaris, 382

iridis retins, 382

lateralis of sacrum, 311

optica, 381, 382 hypothalamica, 339

radiata, 202 Parthenogenesis, artificial, 20 Patella, ossification of, 316 Peduncles of cerebrum, 338 Pelvis, renal, 199, 201 Penis, 143

Perforated space, 346 Pericardial cavity, 49, 53, 179, 180 chick, 53, 60

membrane, 187 Perichondral bone formation, 289, 290 Perichondrium, 287 Periderm, 294 Perilymph space, 387, 389 Periosteal bone formation, 289

lamellae, 290 Periosteum, 287 Pcriotic capsule, 312 Peripheral lymphatics, 279

nervous system, 353

sinus, 281 Periportal ducts, 177 Peritoneal cavity, 53, 185 chick, 53

mesothelium, 170

sac, 133 lesser, 133, 189 Peritoneum, 133 Peroneal artery, 268

nerve, 356 Petrosal ganglion, 93, 116, 364

nerve, superficial, 116, 363

sinus, 273 PflUger's tubes, 215 Phalanges, ossification of, 316 Phallus, 143, 225 Pharyngeal bursa, 162

membrane, 42, 46, 47, 80, 159

plate, 42

pouches, 46, 60, 95, 117, 160

tonsil, 162 Pharyngopalatine arches, 149 Pharynx, human, 81

muscles of, 320

pig, 93, 116 Philtrum, 146 Phrenic artery, 267

nerve, 355 Pia mater, 126 Pig embryos, 112 6 mm., 89 10 to 12 mm., 112 dissection of, 137 transverse sections of 6 mm., 104 of 10 mm., 125

fetal membranes, 68 Pigment granules, 295

layer of retina, 1 26, 377, 381 Pillars, anterior, of fornix, 347

PiUars of Corti, 387

Pineal body or gland, 141, 290, 310, 330, 339

Pisiform, ossification of, 316

Pituitary body, 339

Placenta, accessory, 242

human, 73, 230, 231, 235, 237 cotyledons of, 240 intervillous spaces of, 241 position of, 242 relation of fetus to, 241 vessels of, 241

previa, 242

succenturiate, 242 Placodes, 362

auditory, 385

olfactory, 371

optic, 376 Plasm, germ, continuity of, 4 Plate, alar, 323, 332, 335, 337

basal, 239, 240, 323, 332

blood, 247

closing, 160

cribriform, 313

cutis, 111

floor, 322, 324, 332

lens, 376

muscle. 111

neural, 300

notochordal, 31

roof, 322, 332, 338

urethral, 225 Pleura, parietal, 168

visceral, 168 Pleural cavity, 53, 61, 183, 185 chick, 53

coelom, 96 Pleuro-pericardial cavity, 40

membranes, 182, 183 Pleuro-pcritoneal canal, 183

cavities, 179

membranes, 182, 183 Plexus, brachial, 355

chorioid, 141, 142, 334, 338, 342

lumbo-sacral, 356 Plica semilunaris, 383

venae cavae, 103, 133, 189, 192, 274 vein of, 274 Polar bodies, 18 Polocytes, 18 Polydactyly, 316

Polymorphonuclear leucocytes, 246 Polyphyletic theory of origin of blood elements,

243 Polyspermy, 20 Pons, 115,330

nucleus of, 336 Pontine flexure, 327 Popliteal artery, 268 Portal circulation, 279

vein, 99, 125, 268, 270 Postbranchial bodies, 164 Postnasal gut, 97 Preformation, doctrine of, 2 Pregnancy, abdominal, 20

ovarian, 20

tubal, 20

uterine glands of, 236

uterus during, 230 Premaxillary palate, 373

Premyelocytes. 244, 245, 246 Prepucium, 2ZS, 226 Preverlebrii) ganglia, 368 Primary excretory ducts, 52, 196, 199 Primates, 68

cleavage of ovum in, 27 Primitive choanx, 373

folds, 31

groove, 31, 36. 38

heart, chick, 42

knot or node, 31,36,51

palate, 373

pit, 31

segraeots. 2, 40

streak, 31,36, 40, SI Primoidial follicles. 215 Proajnniotic area, 39. 43 Process, coracoid. 316

costal, 310

fronto-nasal, 372

latetal nasal. 144, 145, 372 palatine, 147

mandibular, 112, 314, 372

mastoid, 314

manillary, 112,314,372

median nasal, 144. 145, 372, 373 palatine. 147

nasal, 372

styloid. 314. 315

vermiform, 172, 174

xiphoid, 311 cleft, 316 Processus globulares, 372 Proncphric ducts, 196

tubules, 49 Pronephros, 52, 195 Pronucleus. 18. 19 Prophase of mitosis, 13 Prosencephalon, 327

chick, 44 Prostate gland, 227

ProsUtic utricle, 218, 219 j

Pubis, ossification of, 316 I

Pulmonary arteries. 99, 121, 122, 168, 258, 262, 264 i

ridge, IJW I

vein, 121, 168, 255 i

Pulp, dental. 157

enamel. 155 Pupillaiy membrane, 381 Pyramids of kidney, 201

Ralhke's pockcl, 57. 59, 81, 93, 126, 160

Recapitulatian, law of, 5

Receptive nucleus. 335

KwEss, inferioi, ol omental bursa, 190

lateral, 334

mammlllary, 330, 341

optic. 330, 34,^ Rectum, 120, 135, 143. 174, 205 Red blood corpuscles, 244, 24S

bone marrow. 289

nucleus, 337 Reference, titles tor, 6 Regeneration of bone, 291 Reicherl's cartilage, 390 Reil's islands, 349 Reissner's membrane. 389 Renal artery, 205, 267

columns, 202

corpuscles, 133. 198, 199

papilla'. 202

pelvis, 199, 201

tubules, 201, 203

veins. 275 Reptiles, cleavage of ovum id, 26

gastrulation of. 28

origin of mesoderm it

testis, 212 Kelicular formation, 335

tissue, 6.1. 285 Retina, layer? of, 382

nervous layer, 126

pigment layer of, 1Z6, 377, 381 Retinal layer. 381

of optic cui). 377 Retroperitoneal sac, 279 Rhinencephalon. 328. 341, 346 Rhombencephalon, 80, 327

chick, 44 Rhombic grooves, 334

lip, 334 Rhombcidial sinus, 40, 44, 50 Ribs. ,MW. 310 Ridge, pulmonary. 183 Rod cells of retina. 382 Rolando's fissure, 351 Roof plate. .132. ,132. 338 Roots, spinal, dorsal, 305

Round ligament. 220, 222

lobe of liver, 192

Radial artery, 268

nerve, 356 Radius, ossification of. 316 Ramus angularis. 270

270

dorsal. 354 gray, ,'67 lateral, 354 posterior. 354 terminal, 354 ventral. 3.M white. ,W6

Sacciili^s. ,186 Saccus vaginalis, 223 Sactal artery, middle, 268 Sacrum, pars lateralis of, 311 Sagittal dissections, median, 140

sinus, superior, 273 Salivary glands, 152 Saphenous vein 277 Sarcolemma, 293 Sarcoplasm. 293 Sarcostyles. 29.1 SalyriiilK-rck. .Wl

++++.d i-cll

.244

Scab tymiwii i vislibuli. 389 I Scapula. ossificalioD of, 316 . Sciatic ner^'e, 356

4o8

INDEX

Sclerotic layer of eye, 383 Sclerotome, 111, 284 Scrotal area, 227 Scrotum, 227

ligament of, 222 Sebaceous gland, 296 Sections, chick, fifty hours, 59 thirty-eight hours, 47 twenty-five hours, 40

pig, 6 mm., 104 10 nrni., 125 SecsseFs pocket, 35, 81, 93, 160 Segmental zone, 64

Segmentation of ovum, 23. See also Cleavage of ovum.

of vertebrate head, 365 Segments, mesodermal, 2, 40, 51, 62, 64

primitive, 2 Semilunar ganglion, 92, 116, 361

valves, 258 Seminal vesicle, 218 Sense cells, 387

organs, chick, 44, 55 human, 80, 370 Sensory nerves, somatic, 357

organs, general, 371 Septa placentae, 240 Septum, atrial, 251

mterventricular, 121, 258

median, of adult spinal cord, 324, 325

membranaceum, 259

nasal, 313, 373

pellucidum, 346, 347

primum, 98, 120, 252, 279

scroti, 227

secundum, 121, 253, 279

spurium, 253

transversum, 61, 62, 83, 113, 116, 143, 175, 180, 182, 183 Sertoli, sustentacular cells of, 14, 213 Sex cells, 208

determination of, 22 Shaft of hair, 296 Sheath cells, 306

hair, 296

medullary, 306

myelin, 306 Shoulder-blade, ossification of, 316 Sinus, blood, 281

cavernosus, 273

cervical, 90, 112

coronary, 253, 271

frontal, 376

marginal, 241

maxillary, 376

peripheral, 281

petrosal, 273

rhomboidal, 40, 44, 50

sagittal, superior, 273

sphenoidal, 376

transverse, 273

urogenital, 120, 205, 212

venosus, 57, 60, 97, 120, 249, 250, 253 valves of, 121, 251 Sinusoids, 86

of liver, 57, 62, 176,268,269 Situs viscerum inversus, 194 Skeletal muscle, striated, 291, 292

system, 309

Skeleton, 309

anomalies of, 316

appendicular, 315

axial, 309

branchial arch, 314 Skull, 311

chondrification of, 312

membrane bones of, 314

ossification of, 312 Smooth muscle, 291 Solitary tract, 362 Soma, 4 Somatic mesoderm, 52, 53, 69

motor nerves, 360

sensory ner%'es, 357 Somatopleure, 30, SSf 52, 53, 62, 64 Somites, 2 Sperm cells, 10 Spermatic artery, 267

cord, 224

veins, 275 Spermatids, 14 Spermatocyte, primary, 14

secondary, 14 Spermatogenesis, 14 Spermatogonia, 14, 213 Spermatozoon, 10 Sphenoid bone, ossification of, 313 Sphenoidal sinus, 376 Spheno-mandibular ligament, 315 Spheno-palatine ganglia, 368 Sphincter muscle of iris, 383 Spina bifida, 352 Spinal accessory nerve, 93, 116, 364

arteries, 264

cord, 322 primitive segments, section through, 111

ganglia, 50, 116,304

supporting cells, 305, 306

nerves, 116, 353 efferent or ventral root fibers of, 302

roots, dorsal, 305

tract, descending, of trigeminal nerv^e, 361 Spiral ganglia, 358, 359

limbus, 387

organ, 386, 387

sulcus, 387

tunnel, 387 Spireme, 13

Splanchnic mesoderm, 53, 69, 169, 366 Splanchnopleure, 30, 34, 52, 53, 64 Spleen, 191, 281 Splenic corpuscles, 282 Spongioblasts, 302, 306, 307 Spongy layer, 236, 240 Stapedial artery, 390

muscle, 390 Stapes, 315, 390 Stenson's canal, 148 Sternal bars, 311

Sterno-clcido-mastoid muscle, 364 Sternum, 311

cleft, 316 Stoerck's loop, 203 Stomach, 81,96, 119, 169 Stomodaeum, 57, 80, 161 Stratified epithelium, 294 Stratum corneum, 294

germinativum, 294

INDEX

400

Stratum granuiosum, 216, 217, 294

lucidum, 294 Stroma of ovary, 215 Study, methods of, 5 Stylo-hyoid ligament, 315 Styloid process, 314, 315 Subcardinal veins, 102, 123, 124, 274 Subclavian arteries, 99, 122, 262, 263, 266, 268

veins, 123, 276 Sublingual gland, 152 Submaxillary ganglia, 368

gland, 152 Substantia ossea, 157

propria of cornea, 377 Sudonparous glands, 297 Sulcus, central, 351

coronary, 225, 251

hypothalamicus, 330, 339

interventricular, 258

limitans, 323, 332, 339

of cerebrum, 351

spiral, 387 Supporting cells, 371, 387 of neural tube, 307 of spinal ganglia, 305, 306

tissue, 285 Suprarenal artery, 267

gland, 143, 368, 369 accessory, 370

vein, 275 Supratonsillar fossa, 161 Suspensory ligament of lens, 381 Sustentacular cells (of Sertoli), 14, 213 Sweat glands, 297 Sylvian fissure, 349 Sympathetic ganglia, 305, 367

nervous system, 366 Synovial membrane, 291

Tactile corpuscles, 371 Taenia, 334 Tail bud, 55

fold, 55

gut, 97

of caudate nucleus, 345 Tarsal glands, 383 Tarsius, origin of mesoderm in, 34 Tarsus, 383

ossification of, 316 Taste buds, 151,371

cells, 371 Teeth, aniages of, 153, 154

anomalies of, 158

cement of, 157

decidual, periods of eruption, 157

dental lamina of, 153 ixipilla, lvS3, 157 pulp, 157 sac, 157

dentine, 157

development of, 153

enamel, 153, 155

milk, iK.Ti()<ls of eruption, 157

o<lontoblasts, 157

of vertebrates, 158

I^ermanent, |)eriods of eruption, 158 Tegmentum, 3v^0 Tela chorioidea, 329, 338

Telencephalon, chick, 56

commissures of, 346

human, 80, 327, 341

pig, 92, 115 Telolecithal ova, 23 Telophase of mitosis, 13 Temporal bone, ossification of, 313

operculum, 349 Tendon, 286 Tensor nerve, 358

nucleus, 335

ramus, 354

tympani, 390

ventricle, 326 Testis, 212

anomalies of, 214

compared with ovary, 217

concealed, 224

cords, 212, 213

descent of, 222

intermediate cords of, 213

interstitial cells of, 213

ligament of, 221

mediastinum, 213

tubuli contorti, 213 recti, 213 septula, 213 Tetrads, 16 Thalamus, 142, 330 Thebesian valve, 254 Theca foUiculi, 217 Theory of concrescence, 31 Thoracic duct, 279 Thoraco-abdominal muscles, 317 Thymic cori^uscles, 163 Thymus, 162

aniages, 82

gland, 118 Thyreo-cervical trunk, 266 Thyreoglossal duct, 117, 164 Thyreoid anlage, 60

cartilage, 166, 315

gland, 118, 164 human, 81,82, 164 pig, <M, 95 Tibia, ossification of, 316 Tibial ner\e, 356

veins, 277 Tissue, adifwse, 287

areolar, 286

connective, 285 white fibrous, 285

corneal, 286

difi^erentiation of, 4

elastic, 286

lymphoid, of si)leen, 282

ner\'ous. 300

reticular. 16w^, 285

supporting, 285 Titles for reference, 6 Toes, suixTnumcrar>', 316 Tomes, dentinal fibers of, 15/ Tongue, muscles of, 320

of pig. 116, 143, 149 fiapilKT of, 151, 152 Tonsil, iKiIatine, 82, 118, 162

I)haryngeal, 162 Tonsillar fossa, 161 Touch-i)acls, v^OO

4IO

INDEX

Trabeculae came, 259

Trachea, human, 81, 82, 164, 166

piK,94,95, 119, 143 Tract, descending, of fifth nerve, 335 Tractus solitarius, 335 Tragus, 391 Trapezius muscle, 364 Triangular ligaments, 192 Tricuspid valves, 121, 259 Trigeminal nerve, 92, 116, 361 Trochlear nerve, 1 16, 330, 361 Trophectoderm, 26, 71, 72, 232 Trophoderm, 232, 234 Tubal pregnancy, 20 Tuber cinereum, 330, 341 Tubercle, cloacal, 225

Darwin's, v^91

genital, 225

MUller's, 221

satyr, 391 Tuberculum acusticum, 358

impar, 82, 94, 117, 150 Tubular heart, 248 Tubules, mesonephric, 197^

and genital glands, origin of, 218

renal, 120, 201, 203 Tubuli contorti, 213

recti, 213

septula, 213 Tunica albuginea, 212, 214

externa, 2i7

interna, 217

vaginalis, 224 Turbinate anlages, 143 Twins, development of, 21 Tympanic cavity, 161, 389

membrane, 117, 391

Ulna, ossification of, 316 Ulnar artery, 268

nerve, 356 Ultimobranchial body, 118, 164 Umbilical arteries, 86, 99, 123, 135, 260, 267

cord, human, 70 of pig, 70

hernia, 70

veins, 259, 261, 268, 271 human, 86 pig, 100, 124

vessels, 70 Umbilicus, 70 Unguiculates, 68 Ungulates, 68

Unipolar ganglion cells, 305 Urachus, 77, 208 Ureter, 120, 135, 199, 208 Urethra, 143, 205, 227 Urethral groove, 225

plate, 225 Urogenital ducts, 144

fold, 197, 208

glands, 144

membrane, 160, 205

opening, 225

organs, 83, 143

sinus, 120, 205, 212

system, 97, 120, 195 Uterine glands of pregnancy, 236

Uterine tubes, 219 Utero-vaginal anlage, 220 Uterus, 219, 220

anomalies of, 221

bicomis, 221

during menstruation, 230 pregnancy, 230

fetalis, 221

fundus of, 220

growth of, 221

infantilis, 221

ligaments of, 221, 222

masculinus, 219

planifundus, 221 Utricle, prostatic, 218, 219 Utriculus, 386 Uvula, 149

Vagina, 219, 220 anomalies of, 221 fomices of, 220 masculina, 218, 219 Vagus ganglia, accessory, 116

ner\'e, 93, 116,362,364 Vallate papillse, 151 Valves, atrio-ventricular, 259 bicuspid, 121, 259 colic, 174 Eustachian, 254 mitral, 259

of coronary sinus, 254 of inferior vena cava, 254 of sinus venosus, 121, 251, 253, 254 semilunar, 258 Thebesian, 254 tricuspid, 121, 259 Vascular system, 243 Vegetal pole, 23

Veins, anterior cardinal, 49, 58, 59, 60, 86, 101, 123, 261, 268, 271 axillary, 276 azygos, 274 basilic, 276, 277 border, 276 brachial, 276 cardinal, 123 anterior, 49, 58, 59, 60, 86, 101, 123, 261, 268,

271 common, 58, 60, 86, 101, 123, 261, 268, 271 left, 97 right, 97 posterior, 58, 62, 63, 86, 102, 123, 261, 268, 274 cephalic, 276, 277 cerebral, 273

common cardinal, 58, 60, 86, 101, 123,261,268, 271 left, 97 right, 97 development of, 268 femoral, 277 gluteal, 277 hemiazygos, 274 hepatic, 270

common, 98 iliac, 274, 275 intersegmental, 274 ischiadic, 274 jugular, 123, 273

INDEX

411

Veins, linguo-facial, 101

lumbar, 276

mesenteric, superior, 99, 100, 125, 270

of extremities, 276

of heart, 86

of lower extremity, 277

of pig, 99, 123

of plica vense cavae, 274

ophthalmic, 273

ovarian, 275

portal, 99, 125, 268, 270

posterior cardinal, 58, 62, 63, 86, 102, 123, 261, 26S, 274

pulmonary, 121, 168, 255

renal, 275

saphenous, 277

spermatic, 275

subcardinal, 102, 123, 124, 274

subclavian, 123, 276

suprarenal, 275

tibial, 277

umbilical, 259, 261, 268, 271 human, 86 pig, 100, 124

vitelline. 49, 62, 86, 99, 124, 182, 260, 268 chick, 39, 40, 42 right, 98 Velum, medullary, 330, v337 Vena anonvma, left, 271 right, 272

capitis lateralis, 273 medialis, 271, 273

cava, inferior, 100, 103, 120, 124, 189, 274, 275 superior, 271

ports, 268, 270 Ventral arteries, 99, 122

ramus, 354 Ventricle, fifth, 347

first, 329

fourth, 115,330

lateral, 115,329

of heart, 57, 83, 90, 97, 249, 251, 258

of lar>'nx, 165

second, 329

terminal, 326

third. 329, 341 Ventricular limb, 249 Ventro-lateral arteries, 99, 122 Vermiform process. 172, 174 Vermis cerebelli, 336 Vernix caseosa, 74, 295 Vertcbnc, 309, 310

chondrification of, 310

ossification of, 310

pig, centra of, 142

variations in number, 316 Vertebral arch, 310

arteries, 122, 264 Vertebrate head, segmentation of, 365 Vesicle, auditory, 3S5

blastodermic, 26

brain, primary, 322, 327

Vesicle, cer\ncal, 161

lens, 376, 379

optic. 40. 43, 47, 59, 343

otic, 45

seminal, 218 V'esicular follicles, 215 Vestibular anlage, 386

ganglia, 358

glands, 228

membrane, 389 Villi, anchoring. 237

of chorion, 71, 72, 232, 237

of intestine, 173

origin of, 72 Viscera, 114

lateral dissections, 138

pig, dissections of, 91 Visceral ganglia, 368

mixed nerves, 361

pleura, 168 Vitelline arteries. 46, 58, 63, 86, 99, 122, 260, 261, 262 chick, 42

circulation, 46

duct. 159

membrane, 7

veins. 49. 62, 86, 99, 124, 182, 260, 268 chick, 40 right, 98 Vitello-umbilical trunk, 86, 260 \'itreous body of eye, 380 Voluntary muscle, 52 Vomer, 314 Vomero-nasal organ, 357, 374

White blood cori>uscles, 245. See also Leucocytes,

commissure, 325

fibrous connective tissue, 285

rami, 366 Whole embryos

for study, 137 Winslow's foramen, 134, 190 WoltVian ducts, 97, 83 

Xiphoid process, 311 cleft, 316

Yellow bone marrow, 2*X) Yolk, 7

sac, 65. W), 67, 68. 77

stalk, 65, 66. 77, 79, 120, 159, 170, 171

ZoN'A pellucida, 7 Zone, ei)endymal, 301

marginal, 302

nuclear, 302

segmental, 64 Zonula ciliaris. 381 Zuckerkanill's l>o<lies, 369 Zygomatic Iwne, 314

E601 Prentiss, u. 110401 fP9S Lab. manual and textb.of 1915 embrvoloev.