ook B COPYRIGHT DEPOSIT GUIDE TO THE Dissection and Study OF THE CRANIAL NERVES AND BLOOD VESSELS OF. THE HORSE BY. GRANT SHERMAN HOPKINS New York State Veterinary College Ithaca, N. Y. SECOND EDITION GUIDE LO; TEE Dissection and Study OF THE CRANIAL NERVES AND BLOOD VESSELS OF THE HORSE SECOND EDITION BY GRANT SHERMAN HOPKINS THE CRANIAL NERVES. Apparent or NAME Real aie Superficial Foramen of Exit Function Deep Origin Ovens rigin I. N. olfactorius. Olfactory epithelium. | Olfactory bulb. E items in the eribriform Sensory. II. N. opticus. Ganglion cells of the Optic chiasma. | Fm. opticum. Sensory. retina. II1. N. oculomotorius. Floor of the aqueduct | Gays cerebri. Fm. lacerum orbitale. Motor. of Sylvius. IV. N. trochlearis. Floor of the aqueduct | Anterior medul- Fm. patheticum. Motor. of Sylvius. lary velum. Motor | Floor of 4th ventricle root. and the pons. { Fm. lacerum basis cranii, | Sensory V.N. trigeminus< Pons. Fm. rotundum, and Sensory | Ganglion semilunare. (| Fm. lacerum orbitale. Motor. root. (Gasserion ganglion.) Floor of 4th ventricle VI. N. abducens. and Medulla. Fm. lacerum orbitale. Motor. gang.geniculatum. Sensory VII. N. facialis. Floor of 4th ventricle. | Medulla. I'm. stylomastoideum. and Motor. VIII. N. acusticus Ganglion spirale and Medulla Meatus acusticus internus. | Sensory. = =) ganglion vestibulare. ie : Floor of 4th ventricle Sensory IX. N. glossopharyngeus. and the ganglion Medulla. Fm. lacerum basis cranii. and petrosum. Motor. Floor of 4th ventricle Sensory X. N. vagus. and the ganglia jug- | Medulla. Fm. lacerum basis cranii. aad ulare and nodosum. Motor. Floor of 4th ventricle | Medulla and XI. N. accessorius. and the ‘spinall cord cervical por- | Fm. jacerum basis cranii. | Motor. asfarbackasthe 6th] tion of spinal or 7th spinal nerve. | cord. XII. N. hypoglossus. Medulla‘ Fm. hypoglossi. Motor. Floor of 4th ventricle. On. A661564 me | on The Cranial Nerves and Blood Vessels of the Horse According to the usualenumeration there are twelve pairs of cranial nerves. The first or olfactory nerve, on either side, consists of numerous soft, gray, non-medullated fibers which are not united into a single nerve trunk but pass through the cribriform plate of the ethmoid bone as numerous small bundles; these several bundles taken together are considered as one nerve. Of the twelve pairs of cranial nerves three are sensory, viz., the olfac- tory, the optic and the acoustic nerves. Five are motor, viz., the oculo- motor, trochlearis, abducens, accessory and hypoglossal nerves. The remain- ing four nerves, viz., the trigeminal, facial, glossopharyngeal and vagus, are mixed nerves. The relation of the motor and the sensory nerves to the brain and spinal cord is radically different. The motor nerve fibers originate from nerve cells that lie within the gray matter of the brain and spinal cord and are distributed principally to the skeletal and visceral musculature. The sen- sory nerve fibers, on the other hand, originate from nerve cells that are situated in the sensory ganglia or the end organs lying wholly outside of the central nervous system. The sensory nerve fibers enter the brain and spinal cord and terminate either directly or indirectly in the respective sense areas and reflex centers of the central nervous system. Under normal conditions the motor fibers are stimulated only at their central origin, i. e., through the nerve cells in the brain and spinal cord from which the fibers originate. The sensory fibers are stimulated only at their endings in the peripheral tissues, the skin, the mucous membrane and the sense organs. Of the purely sensory nerves the first or olfactory originates from the olfac- tory cells of the nasal mucous membrane and passes in the form of numerous soft, gray, non-medullated fibers through the lamina cribrosa of the ethmoid to the olfactory bulb of the brain. The connections established by the nerve fibers that connect the olfactory bulb with the cerebral hemispheres are complicated and in part incompletely known. The optic nerve arises from the ganglion cells of the retina of the eye. From. these cells the nerve fibers pass through the optic nerve and thence to the primary optic centers of the brain. 6 The origin of the acoustic nerve is from two ganglia in the internal ear. Theacoustic nerve consists of two parts, the cochlear and vestibular branches. The cochlear branch arises from the ganglion spirale of the cochlea and the vestibular branch from the ganglion vestibulare of the internal ear. From . these sensory ganglia of origin the nerve fibers pass through the internal acoustic meatus to their respective acoustic and equilibrium centers in the brain. The twelve pairs of cranial nerves as commonly enumerated are given in the preceding table. The part or region of the brain to which the respective nerves are attached is often spoken of as the place of origin of the nerve. It should be kept in mind, however, that the real origin of the respective motor nerves is from a group or nucleus of nerve cells situated within the central nervous system and that the real origin of the sensory nerves is from their respective ganglia or end organs situated outside of the central nervous system. The sensory fibers of the fifth, seventh, ninth and tenth cranial nerves originate from the cells of the ganglia of these nerves. A short distance from the ganglion nerve cells the sensory fibers divide into two branches of which one branch passes into the brain while the other passes to the peripheral tissues as the skin, mucous membrane, teeth, etc., the two branches together constituting a sensory nerve fiber. PREFACE This dissection guide is designed to meet the needs of the student for an orderly and systematic guide to the dissection of the cranial nerves and blood vessels. By exercising a little care nearly all of the parts may be left intact for study and demonstration after the dissection is completed. After completing the dissection of a part, as a nerve or blood vessel, which often must be done piecemeal, it is essential that the student get a compre- hensive idea of the structure as a whole. This idea should be got from the specimen itself. Most students need encouragement to study and to learn the actual object rather than to memorize text-book descriptions of it. Too often the student is unable to identify on the dissected specimen a given structure although he may be able to repeat practically everything that is said of it in the book. The dissection of the nerve supply to the larynx preferably should be done on another larynx. Otherwise the vessels and nerves already dissected, in this region of the head, will be so mutilated as seriously to interfere with their subsequent demonstration. After completing the dissection and study of the head the student should demonstrate his dissection. A satisfactory demonstration necessitates the presentation of visual evidence confirmatory of all oral statements. 9 will be dissected later. The nerves auricularis medius and auricularis posterior and also the three small nerves to the muscles digastricus, stylo- mandibularis, occipito-styloideus and stylohyoideus originate from the N. facialis at the stylomastoid foramen, Pl. IT, 52, 53, 57. The two auricular nerves are readily found but the other three small nerves are covered by a thin aponeurosis and cannot be demonstrated satisfactorily at present. Usually a nerve loop encircles the A. auricularis posterior, Pl. IT, 58. N. auricularis posterior. Carefully remove the skin of the external ear. The N. auricularis pos- terior originates from the N. facialis at the stylomastoid foramen and accom- panies the peripheral portion of the A. auricularis posterior as shown in PI. II, 52. The nerve, covered by the parotid gland, passes dorsally across the base of the styloid process of the occipital bone and is distributed to the pos- terior auricular muscles. Turn aside the overlying structures and trace the nerve as far as possible. A. auricularis posterior. Pl. II, 46. The superficial branches of this artery should now be dissected. The origin of the artery and its deep branch cannot be seen at this stage of the dissection. Of the two superficial branches the larger, posterior branch passes to the posterior part of the ear, near its base, and divides into two branches both of which extend to near the tip of the ear where they anas- tomose with each other; one of these anastomosing branches runs along near the middle of the posterior surface of the external ear and the other ~ near the inner or medial border of the ear. The much smaller of the two superficial branches of the A. auricularis posterior passes along the lateral or external border of the ear and anas- tomoses with the middle branch. A small branch accompanies the N. auricularis medius through the foramen near the base of the styloid process of the conchal cartilage to the inner surface of the ear, Pl. II. N. auricularis medialis or internus. This nerve originates from the N. facialis close to the stylomastoid for- amen, Pl. II, 53. Surrounded by gland tissue, it passes along the styloid process of the conchal cartilage to the foramen near the base of this process through which the nerve passes to the inner surface of the ear. N. auricularis anterior or auriculo-palpebraris. This nerve, as already indicated, originates from the dorsal edge of the N. facialis immediately posterior to the V. temporalis superficialis, Pl. IT, 54. 10 Transect and turn aside the thin M. zygomatico-auricularis and carefully remove the gland tissue which surrounds the nerve. Before the nerve crosses the zygomatic process of the temporal bone it gives off several small branches which supply the anterior auricular muscles. The main portion of the N. auricularis anterior passes anteriorly across the zygomatic process of the squamous temporal bone a little posterior to the mandibular articular surface; here it intermixes somewhat with a branch of the N. lacrimalis, from the 5th cranial nerve, and with it forms a plexus known as the plexus auricularis anterior, Pl. II, 55. The larger portion of the nerve, however, continues anteriorly to the inner canthus of the eye and is distributed to the muscles corrugator supercilii, orbicularis palpebrarum and levator naso-labialis. (The branch to the last mentioned muscle may be traced 10 to 15 cm. below the eye). The branch of the N. lacrimalis which helps to form the plexus auricularis anterior passes through a small groove on the zygomatic process of the temporal bone immediately posterior to the suture between this process and the supraorbital process of the frontal bone and is distributed to the skin at the base of the ear. Ramus colli. This small nerve arises from the N. facialis almost directly opposite the N. auricularis anterior, Pl. II, 59, or occasionally in common with the anterior end of the nerve loop encircling the A. auricularis posterior. It passes obliquely through the parotid gland and then extends along its sur- face, close to the V. jugularis, immediately beneath the aponeurosis which covers the superficial face of the gland. The M. parotido-auricularis receives a filament either from the ramus colli or directly from the N. facialis. The ramus colli receives communicating branches from the second to the sixth spinal nerves. The parotid gland should now be removed in order to expose the small nerves to the muscles occipito-styloideus, digastricus, stylo-mandibularis and stylohyoideus. In removing the gland, if the handle of the scalpel be used pretty largely the danger of injury to the veins and underlying structures will be greatly diminished. Interposed between the deep face of the parotid gland and the subjacent structures is an aponeurosis which is attached principally to the tendons of the sterno-mandibularis and brach- iocephalicus. The three small nerves to the muscles occipito-styloideus, digastricus, stylo-mandibularis and stylohyoideus originate from the ventral edge of the N. facialis, near the stylomastoid foramen. The filament to the M. stylohyoideus can not be readily demonstrated until after the removal of the mandible. “NI Dissection of the Cranial Nerves and Blood Vessels Make an incision in the skin on the median plane from near the free margin of the lower lip to a point opposite the third or fourth tracheal ring. The anterior end of this incision should now be continued dorsally along the margin of the lips as far as to the median plane of the upper lip. A second incision should now be made from the tip of the ear along its lateral margin to its base; continue this incision along the parotid gland and prolong it to the firstincision. Reflect the skin. Care should be taken in reflecting the skin not to include the thin M. cutaneous faciei. This muscle is fairly well defined in the submaxillary space and on the lateral face of the horizontal portion of the mandible (PI. 1,19; Pl. II, 17) but the portion which covers the greater part of the M. masseter is largely aponeurotic. Upon the removal of the skin two large branches of the N. facialis will be seen extending across the M. masseter, covered only by the thin M. cuta- neous faciei. To dissect this latter muscle, begin at its more or less clearly defined border in the submaxillary space and dissect it from the underlying parts. This may be done the more readily if the muscle be transected a little posterior to the large nerve which is supplied to it and the overlying skin by one of the branches of the N. facialis (Pl. I, nerve just below 36). Over a large part of the M. masseter the cutaneous faciei is mostly aponeurotic and this portion of the muscle may be entirely removed. N. facialis, VII. Mixed. This nerve is usually classed as a mixed nerve. The facial nerve proper, however, is purely motor at its nucleus of origin in the dorsal part of the pons. The nerve emerges from the base of the brain immediately caudal to the pons, Pl. VI, 14. The N. facialis passes from the cranial cavity through the internal acoustic meatus and the facial canal of the petrous temporal bone. Closely associated with the facial nervein its course through the facial canal are a sensory nerve— N.interm edius—anda ganglion—Gang. geniculatum— which are often regarded as the sensory part of the facial nerve. This sensory nerve and ganglion however have no nerve connection with the facial nerve and form no integral part of it. The nerve fibers from the geniculate ganglion to the brain constitute the nerve intermedius; the peripheral fibers from the ganglion I2 large nerve with which the N. labialis dorsalis intermixes some distance anterior to the infraorbital foramen is the N. infraorbitalis, a branch of the 5th cranial nerve. Before proceeding farther with the dissection of the nerves the following structures should be demonstrated. Submaxillary lymph gland. Remove the connective tissue from the submaxillary space and note the location, form and size of the submaxillary lymph gland. The gland is V shaped, each arm being from 10 to 12 cm. in length. Parotid duct and the V. maxillaris externa. Trace the V. maxillaris externa to the place where it passes from the submaxillary space across the border of the mandible. Referto Pl. II for an idea of the relations of the parotid duct, the artery and the vein shortly after they cross the margin of the mandible. At this stage of the dissection, veins 28, 29, 30, 31 cannot be seen, as they are covered by the M. masseter; they will be exposed later. Cut the two branches of the N. facialis (dorsal and ventral labial nerves) about 5 cm. anterior to the parotid gland and reflect them from the M. masseter. Now continue the dissection of the parot- id duct and the adjacent portions of the A. and V. maxillaris externa. Trace the parotid duct to its termination in the oral cavity opposite the third superior premolar tooth. Note that the duct is somewhat enlarged just before it opens into the oral cavity. Demonstrate by inserting a probe into the duct a few centimeters from its termination. A. labialis ventralis or inferior. This artery originates from the A. maxillaris externa about 2 cm. ventral to the M. depressor labii inferior, Pl. II, 40;P1.VII,10. It passes obliquely across the deep face of this muscle and continues to the lower lip where it anastomoses with its fellow of the opposite side. It gives off a branch to the angle of the mouth (A. anguli oris) which may anastomose with the A. labialis superior. The A. labialis inferior supplies the M. depressor labu inferior, the inferior molar glands and the lower lip and skin of this region. A. labialis dorsalis or superior. The A. labialis superior is the next large branch of the A. maxillaris externa. It originates near the level of the maxillary or facial crest, Pl. I, 37; Pl. II, 41. It passes beneath the muscles zygomaticus, levator naso- labialis and dilator naris lateralis all of which have previously been turned aside. Trace the artery into the upper lip and demonstrate its anas- 13 tomosis with its fellow of the opposite side; and also its anastomosis with the palatine arteries, by means of a branch which passes through the foramen incisivum of the premaxilla, PI. NWilleno: A. lateralis nasi. This vessel arises from the maxillaris externa a little peripheral to the A. labialis superior, Pl. II, 42. It extends nearly parallel to the A. labialis superior and enters the nasal fossa near the angle formed by the nasal and premaxillary bones. Aa. dorsalis nasi and angularis oculi. These two small vessels may be considered as the terminal branches of the A. maxillaris externa. They arise on the M. levator labii superioris pro- prius and pass under the M. levator nasolabialis, the first to the dorsum nasi and the second to the vicinity of the inner canthus of the eye. A. & V. transversa faciei, Pl. I, 32, 33; Pl. In) 48: Note the relation of this artery and vein to the zygomatic process of the temporal bone and to the facial crest. Note also the small nerve which accompanies the superficial portion of the artery and vein; this small nerve is a branch of the N. temporalis superficialis, as will be demonstrated later. After a short course the artery and vein dip into the M. masseter, a portion of which must be removed in order to demonstrate the course of the vessels, Pl. II, 31, 48. Just after the A. transversa faciei crosses the posterior border of the mandible and gains its lateral face, it gives off a deep branch which, accompanied by a large vein, passes ventrally between the bone and the deep face of the M. masseter (Pl. II, immediately below 61). To expose the vessels just mentioned and also the N. massetericus, proceed as follows: Reflect the proximal portion of the N. facialis from the M. masseter and remove enough of the muscle to expose for a distance of 2 or 3 cm. the deeply situated branches of the A. & V. transversa faciei. The N. mas- setericus is deeply embedded in the muscle and lies from 3 to 4 cm. anterior to the vessels just exposed, Pl. II, 63. To uncover the nerve, make an incision 8 to 10 cm. in length and about one and one-half centimeters in depth, in the M. masseter just ventral of, and parallel to, the A. & V. trans- versa faciei and carefully turn aside the overlying portion of the muscle until the nerve is uncovered. Demonstrate the distribution of the nerve to the M. masseter and then cut it 5 to 8 cm. from the sigmoid notch of the mandible. (The origin of the nerve from the mandibular division of the 5th cranial nerve cannot be demonstrated until after the removal of the mandible, Pl. III, 62). The dissection of the deep branches of the A. & V. 14 transversa faciei, already partially exposed, should now be completed. The artery almost immediately divides into two branches of which the larger is distributed to the M. masseter. The smaller branch is covered by the vein and can be traced for only a short distance, at present. It runs beneath the V. transversa faciei and the zygomatic process of the temporal bone, enters the temporal fossa and anastomoses with the A. temporalis posterior. Each of the above mentioned arterial branches is accompanied by a vein. A. & V. masseterica. The V. masseterica joins the jugular opposite the V. auricularis posterior, Pl. II, 35. It is formed, at the posterior border of the mandible, by two branches one of which comes from the M. masseter and the other from the M. pterygoideusinternus. Trace the masseteric branch and its accompanying artery as far as possible. The vein usually anastomoses with the V. bucci- natoria. The origin of the A. masseterica and the pterygoid branch of the vein will be demonstrated after the mandible is removed. The M. masseter should now be removed as shown in PI. II, but in doing this be careful not to injure the large veins which lie beneath the muscle, Pl. II, 29, 30. These vessels, Vv. buccinatoria and alveolaris, and also the small artery that lies just dorsal to the V. buccinatoria, should be cleaned up as shown in PI. IT. N. ramus transversus faciei. This small nerve accompanies the A. & V. transversa faciei, as already demonstrated. Trace the nerve to its place of origin from the N. temporalis superficialis, Pl. III, 74. At this stage of the dissection the latter nerve usually is not clearly distinguishable from the N. facialis, as the two nerves unite at the place of origin of the ramus transversus faciei and also from this point to its place of origin the N. temporalis superficialis is covered by the surrounding structures. Removal of the mandible. Cut the A. & V. maxillaris externa, the parotid duct, the A. & V. trans- versa faciei, and the A. & V. masseterica at their respective places of crossing the margin of the mandible. All of the horizontal portion of the mandible, except the part anterior to the mental foramen, should now be completely denuded as follows: Begin at the ventral margin of the horizontal portion of the mandible and dissect up en masse all of the overlying structures so that when these are turned dorsally both the upper and lower rows of teeth are exposed. With the saw and chisel cut the ramus of the mandible a little 15 posterior to the mental foramen and also cut it near the place of crossing of the N. facialis. With strong plyers abduct the ramus of the mandible just enough to expose the artery, vein and large nerve that enter the mandibular foramen. All three of these structures should now be cut. Note the small N. mylohyoideus, Pl. III, 72, which lies just posterior to the above men- tioned vessels and nerve, and close to the surface of the bone. Continue to abduct the mandible and at the same time detach from it, as completely as possible, the muscles pterygoideus internus and stylomandibularis; also transect the M. mylohyoideus near its attachment to the mandible. Detach the M. digastricus from the ramus of the mandible and remove the latter. The remaining proximal portion of the mandible, 1. e., the coronoid process and the condyle, are best removed by first detaching, with saw and chisel, the coronoid process from the condyle, but in doing this some care is necessary not to injure the N. massetericus, which passes through the corono-condyloid or sigmoid notch. Now cut the M. pterygoideus externus close to its attach- ment to the mandible and disarticulate and remove the condyle. The zygomatic arch and the coronoid process of the mandible should now be removed. With saw and chisel cut the zygomatic process of the temporal bone near the middle of the condyle and glenoid fossa and at right angles to their long axis; cut the orbital process of the frontal bone just peripheral to the supraorbital foramen and also the malar bone at the level of the maxillary tuberosity of the maxilla. Sever the palpebrae and the periorbita or orbital sheath, to within about 2 cm. of the inner canthus, from their attachments to the rim of the orbit, taking care not to cut the nerve and artery that pass through the supraorbital foramen. Remove the detached portion of the zygomatic arch and also the coronoid process of the mandible; in removing the latter, however, disturb as little as possible the overlying plexus auricu- laris anterior and the M. temporalis, whose insertion completely surrounds the coronoid process. Slit the M. temporalis down to the bone and care- fully detach the muscle from the coronoid process and remove the latter. Before proceeding with the dissection of the nerves, the large V. maxil- laris interna and certain other veins should be noted. V. masseterica (continued). The deep branch of this vein should now be traced into the M. pterygoi- deus internus. A little peripheral to the points where the veins masseterica and auricu- laris posterior open into the V. jugularis, the latter vessel is formed by the union of two large branches, the V. temporalis superficialis and the V. maxillaris interna, Pl. II, 37, 38. 16 V. temporalis superficialis. The V. temporalis superficialis is formed by the union of the veins au- ricularis anterior and transversa faciei. The course of the vein and its relation to the N. facialis are shown in Pl. II, 37. Occasionally the N. facialis lies superficial to the temporal vein. V. auricularis anterior. This vein arises from the anterior face of the external ear and unites with the transversa faciei to form the V. temporalis superficialis. Demonstrate the large branch, V. cerebralis dorsalis, which emerges from the parieto- temporal canal posterior to the postglenoid process of the squamous tem- poral bone, and joins the auricularis anterior shortly before the latter unites with the transversa faciei. The V. transversa faciei has already been traced. V. maxillaris interna. Trace the large V. maxillaris interna, Pl. II, 38, from the V. jugularis along the ventral border of the M. pterygoideus externus. At the alveolar border of the mandible it makes an abrupt S shaped curve and is continued by the large V. buccinatoria, Pl. II, 29. The principal radicles of the V. maxillaris interna are as follows: (1) V.temporalis profunda. This is a large vessel which receives smaller branches from the M. temporalis and from the parieto-temporal canal. Its dissection should be deferred until after the temporal nerves have been dissected. (2) V. dorsalis linguae. This large vein is a satellite of the N. lingualis; it enters the V. maxillaris interna near the alveolar margin of the mandible. _ (3) YV. buccinatoria, Pl. II, 29. This is the direct continuation of the V. maxillaris interna, as mentioned above. It may communicate with the V. alveolaris in the vicinity of the maxillary tuberosity. Its communication with the V. maxillaris externa is shown in PI. II. (4) V. alveolaris, Pl. II, 30. Push aside the orbital fat and trace the vein to the periorbita. Its connection with the ophthalmic vein cannot be seen until after the periorbita has been removed. Venae labiales, Pl. II, 25, 26, 27, 28. Trace the V. labialis communis (Pl. II, 25) from its place of union with the maxillaris externa to the venous plexus near the middle of the cheek. From this plexus, trace the respective labial veins to the lips; also trace the branch which communicates with the V. buccinatoria as shown in Pl. IT, 28. In tracing the latter do not cut the nerve which lies in close proximity to the dorsal surface of the vein, Pl. IT, 65. 17 V. angularis oculi, V. dorsalis nasi and V. lateralis nasi. Pl. I, 27, 28, 29. These branches have already been exposed while tracing the correspond- ing arteries. Cut the various veins that enter the maxillaris interna and turn aside or remove the latter. N. trigeminus, V. Mixed. The apparent origin of the N. trigeminus is from the side of the pons by two roots, of which the larger is sensory and the smaller motor; the fibres of the sensory root, however, really originate from the large ganglion semilunare of the 5th cranial nerve. The fibers of the smaller motor root originate in the pons and mid brain. Within the cranial cavity, the trunk of the N. trigeminus divides into three large branches or divisions, viz., the N. oph- thalmicus, the N. maxillaris and the N. mandibularis, Pl. VI, 12’, 12”, 12”. All of the nerve fibres of the motor root enter the N. mandibularis; a large number of sensory fibres also enter this portion of the 5th nerve thus making it a mixed nerve. The ophthalmic and maxillary divisions of the trigeminus are purely sensory nerves. The N. ophthalmicus passes from the cranial cavity through the foramen lacerum orbitale; the N. maxillaris passes through the foramen rotundum and the N. mandibularis through the fora- men lacerum basis cranii. N. mandibularis. Mixed. The N. mandibularis is made up of both sensory and motor nerve fibres. The nerve, which has a very short course, leaves the cranial cavity by the fo- ramen lacerum basis cranii and, under cover of the M. pterygoideus ex- ternus, divides into several terminal branches as shown in Pl. III, 61. To demonstrate these branches of the N. mandibularis first identify the two large nerves, N. lingualis and N. alveolaris inferior, Pl. III, 69, 71, which extend across the outer surface of the M. pterygoideus internus, and trace them towards the base of the skull as far as to the edge of the M. pterygoideus externus from beneath which the two nerves emerge. The M. pterygoide- us externus must not be removed but simply pushed aside just sufficiently to expose clearly the origin of the nerves. Branches of the N. mandibularis. (1) N. alveolaris inferior. Sensory. This nerve arises from the N. mandibularis in common with the N. lingualis, Pl. III, 69, 71. It passes through the alveolar canal of the man- dible and upon emerging at the mental foramen it divides into several branches known as the mental nerves, which are distributed to the chin and 18 the lower lip, Pl. II, 64a. With a chisel, expose the nerve, artery and vein alveolaris inferior in their course through the alveolar or mandibular canal. As already mentioned, the Nn. mentales are simply the terminal branches of the N. alveolaris inferior. Trace them into the lower lip. Just before emerging from the mental foramen the N. alveolaris inferior gives off a branch that extends through a small osseous canal to the roots of the canine and incisor teeth. To demonstrate this small branch, medisect the lip and chin and remove the one half from their attachment to the mandible and turn them aside. Now carefully chisel away the bone and trace the nerve to the roots of the teeth. (2) N. mylohyoideus. This small nerve was noted when removing the mandible. Trace it to its origin from the N. mandibularis and to its termination in the M. mylo- hyoideus, the anterior portion of the M. digastricus and the skin of the anterior part of the submaxillary space, Pl. III, 72. The filament to the M. digastricus is given off near the posterior border of the M. mylohyoideus. The N. mylohyoideus may appear to originate from the N. alveolaris inferior; the fibres, however, can readily be separated from this nerve and traced back to the N. mandibularis. Gl. sublingualis. Reflect the M. mylohyoideus and identify the sublingual salivary gland, Pl; 1,-35; Pl. VIII, fea, 8, “It 1stirom 12 to 15 em. in length and from 2 to 3 cm. in width. Note the sublingual crest and the 20 to 30 small openings of the ducts of the sublingual gland. (3) N. lingualis. Sensory. The N. lingualis arises from the mandibularis in common with the N. alveolaris inferior, Pl. III, 69. The two nerves pass between the muscles pterygoideus externus and internus and soon diverge from each other, the lingual nerve lying to the inner side and somewhat anterior to the N. alveo- laris inferior. Near the place where the N. lingualis diverges from the alveolaris inferior, it is joined by the chorda tympani, a small nerve which originates within the facial canal of the petrous temporal, from the genicu- late ganglion of the N. intermedius. Demonstrate as much of the chorda tympani as possible. At the anterior border of the M. pterygoideus in- ternus the lingual nerve passes between the muscles mylohyoideus and styloglossus between which it extends as far as to the posterior end of the sublingual salivary gland where it passes beneath the gland and the M. sty- loglossus deep into the tongue. Dissect up the ventral edge of the sublingual 19 gland and turn it dorsally. Trace the nerve to the point where it dips be- tween the muscles styloglossus and genioglossus. Further dissection should be deferred until after the N. sublingualis has been dissected. The N. lingual- is gives off several small branches to the region of the maxillary tuberos- oye Wa: (4) N. sublingualis. Sensory. This small nerve arises from the dorsal edge of the N. lingualis opposite, or a few centimeters from, the anterior edge of the M. pterygoideus internus, Pl. III, 70. Upon reaching the sublingual gland the nerve dips beneath it and accompanied by the sublingual artery and vein and the duct of the sub- maxillary salivary gland, all of which should now be studied, runs the whole length of the sublingual gland and terminates in the mucous membrane of the anterior portion of the floor of the mouth. Numerous small branches are given off from the N. sublingualis to the mucous membrane of the tongue and oral cavity. Demonstrate the termination of the submaxillary duct at the caruncula sublingualis. The N. lingualis, after giving off the sublingual, passes between the mus- cles mylohyoideus and styloglossus to the posterior extremity of the sub- lingual gland, as already mentioned. Here it turns obliquely across the ventral border of the M. styloglossus and extends along the inner surface of the muscle to the tip of the tongue. Demonstrate the numerous branches given off from the dorsal edge of the lingual nerve in its course between the muscles of the tongue. These branches extend to the mucous membrane of the anterior two-thirds of the dorsum of the tongue. (5) N. massetericus (continued). This nerve should now be traced from the point where it was cut, 5 to 8 cm. from the sigmoid notch of the mandible, to its place of origin from the N. mandibularis, close to the base of the skull, Pl. III, 62. From its place of origin it extends laterally, immediately anterior to the temporo- mandibular surface of the temporal bone and through the sigmoid notch of the mandible as already noted. Near its origin it usually gives off two branches, the Nn. temporales profundi, both of which should be traced into the temporal muscle, Pl. III, 63. The mass of fatty tissue in the orbit should now be removed after first demonstrating the small artery supplied to it. (6) N. buccinatorius. Sensory. The N. buccinatorius may be readily found at the antero-internal surface of the V. buccinatoria, Pl. II, 65. Opposite the last molar tooth the nerve 20 passes between the M. depressor labii inferioris and the mucous membrane of the cheek and accompanies the inferior labial artery and vein to the lower lip. In this part of its course numerous branches are given off to the inferior molar glands and to the mucous membrane of the cheek and lower lip; one or more small branches may be traced to the upper lip in the immediate vicinity of the commissure. Now trace the nerve toward its place of origin from the N. mandibularis. Opposite the maxillary tuberosity it gives off several small branches to the superior molar glands and to the mucous mem- brane of the cheek. The N. buccinatorius passes between the maxillary tuberosity and the anterior border of the M. pterygoideus externus and thence through the M. pterygoideus externus which must be divided longi- tudinally in order to expose the nerve; do not, however, disturb the muscle more than is necessary clearly to expose the nerve, Pl. III, 64. (7) N. temporalis profundus anterior. This small nerve originates from the N. mandibularis. It lies on the dorsal surface of the N. buccinatorius along which it extends to near the anterior border of that portion of the M. pterygoideus externus which is dorsal to the nerve, Pl. III, 8. It then bends dorsally, as shown in Pl. III, 65, and immediately enters the temporal muscle. (8) N. pterygoideus externus. This small nerve originates from the N. mandibularis and almost im- mediately enters the inner or deep surface of the external pterygoid muscle. Very frequently the nerve consists of two nearly parallel portions, Pl. III, 67. (9) N. pterygoideus internus. The nerve to the M. pterygoideus internus is much larger than the one to the M. pterygoideus externus. It originates from the N. mandibularis and is partly covered by the dorsal edge of the common trunk of the nerves lingualis and alveolaris inferior. The nerve enters the muscle at its posterior border, Pl. III, 68. (10) N. temporalis superficialis. Sensory. This is a large sensory branch which originates from the N. mandibularis and joins the facial nerve at the posterior border of the mandible, Pl. III, 74. It gives off several small branches one of which, ramus transversus faciei, accompanies the artery and vein of the same name for some distance across the M. masseter as has already been demonstrated; one small branch, ramus auricularis, accompanies the anterior auricular artery and vein to the ear. Numerous small filaments go to the parotid gland and to the external ear. N. ophthalmicus. Sensory. The N. ophthalmicus is the smallest of the three principal branches of the N. trigeminus. It originates from the semilunar ganglion and, for a short distance, is closely joined to the N. maxillaris but within the orbital hiatus the two trunks are separated by the thin osseous plate that separates the foramen lacerum orbitale from the foramen rotundum. Within this os- seous canal the nerve divides into three branches, viz., N. lacrimalis, N. frontalis or supraorbitalis, and the N. nasociliaris, all of which are sensory. . To expose the nerve proceed as follows: With the handle of the scalpel, free from its attachment to the bone the portion of the temporal muscle that intervenes between the orbit and the M. pterygoideus externus, taking care not to break the artery that emerges from the temporal foramen; also simi- larly detach the portion of the M. pterygoideus externus that is attached to the region between the orbital hiatus and the alar or pterygoid foramen. Slit open the periorbita a little posterior to its point of connection with the V. alveolaris. Note on a prepared skull the relations to each other of the foramen patheticum, the foramen lacerum orbitale and the foramen rotun- dum. With a small chisel carefully remove enough of the bony plate that forms the lateral wall of the orbital hiatus to expose clearly the Nn. ophthal- micus and maxillaris; care should be taken not to disturb the small N. trochlearis which emerges from the foramen patheticum. Upon drawing aside the periorbita three nerves are visible, viz., the lacrimalis, the frontalis or supraorbitalis and the orbitalis. [The N. orbitalis is a branch of the N. maxillaris and will be dissected with that nerve.| : (1) N.Jacrimalis, Sensory. Pl. IV, 27. This consists of several small branches which pass directly to the lacrimal gland and the upper eyelid. One of the larger branches, however, pierces the periorbita, passes posterior to the orbital process of the frontal bone and helps to form the plexus auricularis anterior. This branch of the N. lacri- malis supplies filaments to the skin of the temporal region and the base of the ear, as already noted when dissecting the N. auricularis anterior. (2) NN. frontalis. Sensory. This nerve is of about the same size as the lacrimal and for some distance from its origin lies immediately dorsal to the N. lacrimalis, Pl. IV, 25. Within the orbit it is enclosed by the periorbita until within 2 to 4 cm. of the supraorbital foramen when it pierces the periorbita and then lies b tween this membrane and the bone, Pl. IV. After passing through the 22 supraorbital foramen the nerve divides into several small branches which join with the terminal filaments of the N. auricularis anterior, and are dis- tributed to the skin of the forehead and upper eyelid. (3) N. nasociliaris. Sensory, Pl. IV, 26; Pl. V, 28. The N. nasociliaris has the same general course as the A. ophthalmica and lies close to either the dorso-lateral or convex side, Pl. V, 28, or fre- quently at the concave side of the artery. At its origin it is covered by the Nn. lacrimalis and frontalis. To expose the nerve, dissect up the muscles rectus dorsalis and levator palpebrae dorsalis and transect them at about one or two centimeters from their attachment to the globe of the eye,Pl. V, 7, 8. Beneath the M. rectus dorsalis the nerve divides into two main branches, Pl. V, 29, 30, of which one branch, N. ethmoidalis, accompanies the ophthalmic artery through the ethmoid foramen into the cranial cavity and thence passes through the cribriform plate and is distributed to the mucous membrane of the nasal fossa. The other branch, N. infratrochlearis, is of about the same size as the ethmoidal branch. It extends along the ventral surface of the M. trochlearis or obliquus dorsalis as far as to the trochlea or pulley through which the muscle passes. Before attempting to trace the nerve farther first expose the terminal tendon of the muscle troch- learis or obliquus dorsalis and transect it close to the trochlea. The nerve may now readily be traced to the nasal canthus of the eye where it 1s distrib- uted to the skin, the membrana nictitans and the lacrimal apparatus in this region. Some of the filaments extend several centimeters beyond the nasal canthus of the eye. A small branch extends from the N. nasociliaris to the ciliary ganglion constituting the long or sensory root of the ganglion (radix longa ganglii ciliaris), Pl. V, 32. N. maxillaris. Sensory. The origin of this division of the trigeminus from the semilunar ganglion of the fifth cranial nerve and its position immediately ventral to the N. ophthalmicus have already been noted. Carefully free the nerve and adjoin-_ ing arteries, Pl. IV, 30, and Pl. V, 25, of surrounding fatty tissue noting mean- time the three or four small nerves extending to the region of the max- illary tuberosity. The N. maxillaris divides into three branches, viz., N. orbitalis, N. infraorbitalis, and N. sphenopalatinus. (1) N. orbitalis. Sensory, Pl. IV, 28. The nerve orbitalis arises from the N. maxillaris before the latter passes through the foramen rotundum. It enters the periorbita or ocular sheath >2 =a) and soon divides into two or more branches which extend between the periorbita and the M. rectus externus to the lateral canthus of the eye and are distributed to the lower eyelid. (2) N. infraorbitalis. Sensory. The N. infraorbitalis is simply the continuation of the greater portion of the N. maxillaris through the infraorbital canal. With saw and chisel expose the nerve by opening the maxillary sinus and the osseous canal through which the nerve passes. At the infraorbital foramen the nerve divides into three portions, a dorsal, a middle and a ventral, Pl. II, 68, 69, 70. The small dorsal portion, N. nasalis dorsalis or N. nasalis externus, consists of one or more branches which accompany the M. levator labii superiorus proprius and are distributed to the skin on the dorsum of the nose and the nasal diverticulum. The middle portion, N. nasalis anterior, is much larger than the preceding. It enters the anterior portion of the nasal fossa usually by two branches as shown in Plate II. The smaller of these two branches is distributed to the mucous membrane of the anterior part of the nasal fossa; the larger branch is continued to the skin of the upper lip. The ventral portion, ramus labialis dorsalis, is the largest of the three por- tions. It divides into numerous branches which intermix with the fibres of the N. labialis dorsalis of the facial nerve and are distributed to the skin and tactile hairs of the upper lip. The small branch, ramus alveolaris maxillae incisivus, supplied to the canine and incisor teeth, arises from the N. infra- orbitalis in the anterior part of the infraorbital canal. Two to four centi- meters before reaching the infraorbital foramen the ramus enters a small canal in the superior and premaxillary bones and runs in this canal to the roots of the canine and incisor teeth. With a small chisel expose the nerve throughout its intraosseous course, or see laboratory specimen already exposed. The small nerves to the maxillary sinus and the superior molar teeth also arise from Nn. maxillaris and infraorbitalis. Transect the N. infraorbitalis near its entrance to the infraorbital canal and turn aside the proximal part. (3) N. sphenopalatinus. Sensory. The N. sphenopalatinus arises as a large somewhat flattened nerve from the ventral side of the N. maxillaris and passes directly to the sphenopalatine foramen, Pl. V, 41. Closely attached to the dorso-medial surface of the nerve are numerous ganglia (ganglia sphenopalatina or Meckel’s ganglion) which are scattered along the nerve for a distance of 2 to 4 cm, Pl. V, 42. A magnifying glass may be necessary to bring out clearly these small ganglia. 24 Note the numerous small filaments, a score or more, extending from the dorsal side of the ganglia to the periorbita. Some of these filaments pass through the periorbita to the structures within. Numerous filaments from the sphenopalatine ganglia join the Nn. sphenopalatinus, palatinus major and palatinus minor. Immediately after passing through the sphenopala- tine foramen the N. sphenopalatinus divides into two nearly equal branches, a lateral or external branch and a medial or internal branch (see laboratory specimen). The lateral branch runs along theinferior turbinated bone and is distributed to its mucous membrane and to that of the middle and ventral nasal meati. The medial branch, N. septi narium, leaves the main trunk at nearly a right angle and passes to the posterior end of the nasal septum and then extends anteriorly towardsthe prenares. It lies near the ventral edge of the nasalseptum and is distributed to the mucous membrane of the septum and also to the mucous membrane of the anterior portion of the hard palate. (4) N. palatinus anterior or major. Sensory. This large nerve arises from the N. sphenopalatinus and accompanies the anterior palatine artery through the palatine canal and groove, PI. V, 43. Expose from within the maxillary sinus the nerve and artery in’ their course through the palatine canal. In the palatine groove the nerve forms a kind of plexus around the artery. It is distributed principally to the mucous membrane of the hard palate but also sends some filaments through small foramina in the bones of the hard palate to the mucous mem- brane of the nasal fossa. (5) N. palatinus posterior or minor. This small nerve arises from the ventral edge of the sphenopalatine nerve in common with some of the fibres of the N. palatinus anterior. It passes through the groove formed by the maxillary tuberosity and the palatine bone and is distributed to the soft palate, Pl. V, 44. N. canalis pterygoidei (Vidii). First demonstrate on a cleaned skull the two foramina of the pterygoid or vidian canal. Now lift up the A. maxillaris interna and the N. spheno- palatinus a little from the bone and note the vidian nerve extending from the anterior foramen of the canal to the posterior part of the sphenopalatine ganglion. (The N. canalis pterygoidei is formed by the union of the super- ficial petrosal branch of the N. facialis with a sympathetic filament). 25 Summary of the Branches of the N. Trigeminus or 5th Cranial Nerve The N. trigeminus divides into three principal branches, viz., the N. ophthalmicus, the N. maxillaris and the N. mandibularis. The first two are sensory and the last isa mixed nerve. The N. mandibularis supplies the muscles of mastication, viz., the masseter, the temporal and the two ptery- goids; also the mylohyoid and the anterior belly of the digastric; it also supplies sensory branches as follows: the temporalis superficialis, the buc- cinatorius, the lingualis and sublingualis, the rami dentales and mentales. The N. ophthalmicus divides into three branches, viz., the N. frontalis, the N. lacrimalis and the N. nasociliaris. The N. maxillaris supplies the follow- ing branches: N. orbitalis, N. infraorbitalis, Nn. palatinus major and minor and the N. sphenopalatinus. N. oculomotorius. III. Motor. This nerve supplies all the extrinsic muscles of the eye except the obliquus dorsalis or trochlearis, the rectus externus and the retractor oculi. The superficial origin of the nerve is from the crus cerebri. It passes from the cranial cavity through the foramen lacerum orbitale and is here covered by the three branches of the N. ophthalmicus. At the apex of the orbit the nerve divides into a small dorsal branch and a much larger ventral branch, Pl. V, 33, 34. The dorsal branch is short and supplies the muscles rectus dorsalis and levator palpebrae dorsalis. It enters the rectus dorsalis about two centimeters from the origin of the muscle and near its lateral border. The very small filament to the levator palpebrae dorsalis may be found best by raising somewhat the latter muscle from the rectus dorsalis and carefully removing the intervening connective tissue. The filament enters the muscle at its inner or deep face near the middle of the muscle. By using a magnifier the filament may easily be recognized and traced to its place of origin from the dorsal branch of the N. oculomotorius. Usually it is more or less embedded in the M. rectus dorsalis. The ventral branch of the N. ocu- lomotorius is much larger and longer than the dorsal branch. Before attempting to follow this ventral branch, which passes between the tendons of origin of the rectus dorsalis and rectus externus, first dissect the branch of this nerve that supplies the M. obliquus ventralis. This branch lies between the adjacent borders of the external and ventral recti muscles, Pl. IV, 29. Trace it to its termination in the ventral oblique muscle. Transect the M. tectus externus near its middle and reflect the proximal end. Now follow the branch that supplies the M. obliquus ventralis to its place of origin from the ventral branch of the oculomotor, taking care not to disturb 26 the small ciliary ganglion which lies close to the place of origin of this branch from the oculomotor, Pl. V, 38. Usually the ciliary ganglion is so small that it cannot be seen clearly with the unaided eye; by using a magnifying glass, however, it can be seen satisfactorily. Near the origin of the branch to the M. obliquus ventralis the ventral branch of the N. oculomotorius terminates in several large short branches of which two or three enter the rectus ventralis and one or more equally large branches enter the rectus internus, Pl. V. No special dissection is necessary to demonstrate the large branches just mentioned. Ganglion ciliare (Ophthalmic ganglion). This small ganglion les directly against the ventral branch of the N. oculomotorius and is connected to it by one or more very short branches from that nerve, which branches constitute the motor or short ciliary root of the ganglion (radix brevis gangli ciliaris). The sensory or long ciliary root of the ganglion (radix longa gangli ciliaris) is formed by a branch from the N. nasociliaris, Pl. V, 32. From the ciliary ganglion and its sensory root are given off the several ciliary nerves which accompany the optic nerve to the globe of the eye. [The ganglion is more easily demonstrated in the cat than in the horse.] N. abducens, VI. Motor. Pl. VI, 13. The superficial origin of the N. abducens is from the medulla, immediately posterior to the pons. It passes from the cranial cavity into the orbit through the foramen lacerum orbitale and divides into two branches the larger of which enters the M. rectus externus at its inner face, near the origin of the muscle. The smaller branch enters the M. retractor oculi, a short dis- tance from its origin, and is the only nerve supplied to this muscle, Pl. V, 36. N. trochlearis or patheticus, IV. Motor. The superficial origin of the N. trochlearis is from the anterior medullary velum immediately posterior to the quadrigemina. It passes through the smallest of the three suprasphenoidal grooves and emerges from the cranial cavity through the foramen patheticum, Pl. IV, 24, and Pl. V, 31. The nerve extends from this foramen directly to the M. trochlearis or obliquus dorsalis which it enters at its dorso-lateral border at a point about half-way between the place of origin of the muscle and the trochlea or pulley through which the muscle passes. 27 N. acusticus, VIII. Sensory. The apparent origin of this nerve is from the side of the medulla imme- diately caudal to the N. facialis, Pl. VI, 15. Its real origin, however, is from the spiral and vestibular ganglia of the internal ear. It passes through the internal auditory meatus with the N. facialis. Submaxillary salivary gland. To expose this organ, transect the M. pterygoideus internus just ventral to the N. lingualis and remove the detached portion of muscle. Turn the M. stylomandibularis dorsally. The submaxillary salivary gland extends from beneath the wing of the atlas to the basihyoid or body of the hyoid bone. It is from 20 to 25 cm. in length and from 2 to 4 cm in width, al- though the cervical or posterior end is sometimes much wider. The gland is somewhat crescent shaped and is surrounded by a thin fibrous capsule. Turn the gland dorsally noting meantime any small arteries supplied to it. Trace - its duct, which extends along the deep face of the gland nearly the whole length of the organ and is continued anteriorly to the caruncula sublingualis where it opens into the oral cavity. Nerve filament to the M. stylohyoideus. This very small filament extends along the outer face of the proximal por- tion of the M. stylohyoideus for a distance of several centimeters. Trace the filament to its place of origin from the N. facialis, Pl. III, 77. Exposure of the A. carotis communis. Remove the aponeurosis covering the V. jugularis and the adjoining muscles. Turn aside the M. sterno-mandibularis taking care not to cut the nerve that enters its deep face at the level of the V. maxillaris externa. Now turn aside the M. subscapulo-hyoideus in order to expose the trachea, the oesophagus (if on the left side), the thyreoid body, the A. carotis communis and the common trunk of the vagus and sympathetic nerves, Pl. III, 28, 29, 30, 36, 89. Spend some time in studying the relations to each other of the parts just mentioned. Note the relation of the thyreoid body to the angle formed by the jugular and external maxillary veins and also the relation of the jugular vein to the carotid artery. V. thyreoidea. This large vessel arises from the thyreoid body principally, but also from the superior cervical lymph gland and the posterior pharyngeal region, and terminates in the V. jugularis at nearly the same level as the V. maxillaris externa. Another vein from the muscles of the dorsal part of the neck enters the jugular at about this same level. 28 V. occipitalis. This large vein emerges from beneath the wing of the atlas and opens into the jugular about 5 cm. peripheral to the V. maxillaris externa. Anterior cervical lymph gland. This gland is situated in the triangular space formed by the jugular and external maxillary veins and the posterior border of the submaxillary salivary gland. The gland may form two or more separate masses the larger of which, six or more cm. in length in this specimen, lies at the side of the carotid artery; the smaller mass, 2 to 3 cm. in length, lies between the thyreoid body and the submaxillary salivary gland. This lymph gland is supplied with blood by a small branch from the A. thyreoidea superior. A. carotis communis, Pl. III, 36. Trace this artery to the point where, under cover of the submaxillary salivary gland, it divides into its three terminal branches, viz., A. occipitalis, A. carotis interna and A. carotis externa, Pl. III. 38, 39, 40. Collateral branches of the A. carotis communis. (1) Several small branches to the oesophagus, the trachea and to some of the ventral muscles of the neck. (2) Wis SOR CORSE OME 10. PLATE VI Dura. Medulla. Cerebellum. Pons. Cerebrum. Hypophysis. Chiasma opticum. Bulbus olfactorius. PPPPPPPPPP PPP EZZZZ 2222222227 . opticus, . oculomotorius. . trochlearis. trigeminus. This trunk divides into three subdivisions, viz., . ophthalmicus, . maxillaris. . mandibularis abducens. facialis. acusticus. glossopharyngeus. vagus. accessorius. hypoglossus. irst spinal nerve. cerebrospinalis. spinalis ventralis. basilaris. cerebelli posterior. carotico-basilaris. cerebelli anterior. carotis interna. intercarotica. cerebri profunda. . choroidea anterior. . communicans posterior. . cerebri media. . cerebri anterior. This either fuses with its fellow of the opposite side as in the present case, or is joined to it by a transverse branch called A. communicans anterior. Ne A. As meningea anterior. corporis callosi. ethmoidalis See Pl. VIII, fig. 2. Nasal branch of the A. ethmoidalis. See Pl. VII, fig. 2. PLATE VI a. (Pl. VI, 21) A. cerebrospinalis. ” , 22) A. spinalis ventralis. Rami medullares. 4(Pl. VI, 23) A. basilaris. I 2 (é 3 4 Gy ell 6 (@ 7 We Sas OG 10 (cs Il ce 12 (es Te (CS 14 Gs ry . VI. 24) A. cerebelli posterior. 25) A. carotico-basilaris. 27) 29) A. A. carotis interna. 28) A. . choroidea anterior, . communicans posterior. . cerebri media. . cerebri anterior. . meningea anterior. . corporis callosi. intercarotica. cerebri profunda. 16 A. cerebri posterior (Not named in Pl. VI but are represented by the two small arteries immediately posterior to the hypopbysis, No. 6). 17 (Pl. VI. 26) A. cerebelli anterior. PLATE VII FACIAL REGION IN PERSPECTIVE I’. M. levator nasolabialis, cut and turned aside. M. levator labii superioris proprius. 3’. M. dilator naris lateralis, cut and turned aside. 4’. M. zygomaticus, cut and turned aside. M. masseter. M. buccinator. M. depressor labii inferioris. M. cutaneons facie. A. maxillaris externa. 10. A. labialis ventralis or inferior. 11. A. labialis dorsalis or superior. 12. A. lateralis nasi. 13. Small artery to nasal region. 14. A. dorsalis nasi. 15. A. angularis oculi. 16. Terminal branches of the A. palato-labialis. These branches anas- tomose withthe dorsal nasal and the superior labial; they also give off branches to the upper lip and the nostrils. 17. V. maxillaris externa. 18. N. facialis. 19. N. infraorbitalis. 20. Ductus parotideus. 21. Tongue. 22. Caruncula sublingualis. COI AMY Yn fisti Lite ¥ td 9. LO: aby i 12. 13) 14. 15. 16. Qe OW OW No PLATE VIII FIGURE 1. Naris. Tongue. Mandible. M. zygomaticus. M. buccinator (a portion of this muscle has been removed to show the sublingual salivary gland). M. masseter. 7’. M. depressor labii inferioris. Glandula sublingualis with its numerous ducts which open into the oral cavity. A. maxillaris externa. A. labialis ventralis or inferior. A. angularis oris. V. maxillaris externa. 13‘, 13°. Vv. labiales. Ductus parotideus. N. buccinatorius. N. alveolaris inferior. FIGURE 2. Frontal sinus. Ethmoid bone. Fossa ethmoidalis. On the right side a portion of the frontal bone has been removed in order to show the extent of the ethmoid fossa and the blood vessels in it. Portion of falx cerebri. A. communicans posterior. A. cerebri media. A. cerebri anterior. A. corpus calosi. A. meningea anterior. A. ethmoidalis. . Ir‘, Rete ethmoidale. Nasal branches of A. ethmoidalis. Chiasma opticum. Part of hypophysis. PLATE VIII BRell. 21. j ~ on DANAfwWN A Stylohyoid (great cornu). Ceratohyoid (small cornu) Thyreohyoid, end cut off (thyroid cornu). Glossohyoid (lingual process). Thyroid cartilage partially cut away. Cricoid cartilage. Arytenoid cartilage. Epiglottis. Trachea. Soft palate. Root of tongue. . Pharyngeal wall turned back. Posterior pillar of soft palate. Oesophagus. M. cricothyroideus, cut. M. cricoarytenoideus dorsalis, cut and one end turned aside, M. cricoarytenoideus lateralis. M. ventricularis (or part of the M. thyroarytenoideus), Laryngeal saccule. 20. Cut edge of pharyngeal mucous membrane. PLATE IX 28. 29. * 30, Bie Thyreoid body. A. carotis communis. A. maxillaris externa. A. lingualis. N. laryngeus superior (sensory). N. laryngeus inferior (recurrent laryngeal) (Motor). Branch of the N. laryngeus inferior which supplies the cricoaryte- noeideus dorsalis and the arytenoideus transversus. The branch to the M. cricoarytenoideus dorsalis is not shown in the drawing. It is given off beneath the cricoarytenoideus dorsalis and immedi- ately enters the deep face of the muscle. The branch to the M. arytenoideus transversus is No. 28. Branch of the N. laryngeus inferior to the M. arytenoideus transversus. Branch of the N. laryngeus inferior to the M. cricoarytenoideus later- alis. 30. Branches of the N. laryngeus inferior to the Mm. vontrie- ularis and vocalis. 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