DIRECTIONS

FOR THE

Dissection and Study

OF THE

CRANIAL ‘NERVES AND

BLOOD VESSELS

OF

THE HORSE

DIRECTIONS

FOR THE

Dissection and Study

OF THE

CRANIAL NERVES AND
BLOOD VESSELS

OF

THE HORSE

BY GRANT SHERMAN HOPKINS

THE CRANIAL NERVES.

OF Ten
Wer

NAME

Real or
Deep Origin

Apparent or
Superficial
Origin

Foramen of Exit

Foramina in the cribriform

\A\3

Function

I. Nn. olfactorii. Olfactory epithelium. | Olfactory bulb. eel Sensory.
II. N. opticus. Gagetion cells of the | Optic chiasma. | Fm. opticum. Sensory.
retina.
III. N. oculomotorius. F ergs ee eee Crus cerebri. Fm. lacerum orbitale. Motor.
- Floor of the aqueduct | Anterior medul- .
IV. N. trochlearis. epSvies lary velum or Fm. patheticum. Motor.
Motor | Floor of 4th ventricle
2 , root. and the pons. Fm. lacerum basis cranii, | Sensory
V. N. trigeminus q . Pons. Fm. rotundum, and
Sensory} Ganglion semilunare. Fm. lacerum orbitale. Motor
root. | (Gasserion ganglion.)
VI. N. abducens. Floor of 4th ventricle. | Medulla. Fm. lacerum orbitale. Motor
Sensory
VII. N. facialis. Floor of 4th ventricle. | Medulla. Fm. stylomastoideus. and
Motor
VIII. N. acusticus Ganglion spirale and Medulla Meatus acusticus internus. | Senso
2 pa ; ganglion vestibulare. : ; BY
Floor of 4th Ventricle Sensory
IX. N. glossopharyngeus. and the ganglion pe- |Medulla. Fm. lacerum basis cranii. and
trosum. Motor
Floor of 4th ventricle Sensory
X. N. vagus. and the ganglia jug- | Medulla. Fm. lacerum basis cranii. and
ulare and nodosum. Motor
Floor of 4th ventricle | Medulla and
. and the spinal cord cervical por- : «
XI. N. accessorius. as far back as the 6th| tion of spinal Fm. lacerum basis cranii. |Motor.
or 7th spinal nerve. cord.
XII. N. hypoglossus. Floor of 4th ventricle. | Medulla. Fm. hypoglossi. Motor.

Byes

©clA361126

4 J

The Cranial Nerves and Blood Vessels
of the Horse

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 first incision. Care should be taken in reflect-
ing 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 (Pl. I, 19; Pl. II, 17) but the
portion which covers the greater part of the M. masseter is largely aponeuro-
tic. 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. cutaneous 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 th@®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.

The superficial origin of the N. facialis is from the medulla immediately
posterior to the pons. The nerve passes from the cranial cavity through
the facial canal of the petrous temporal bone. In its course from the
stylomastoid foramen, the external orifice of the facial canal, to the pos-
terior border of the mandible the nerve is deeply covered by the parotid
gland. Near the border of the mandible the nerve divides into two large
branches (Pl. I, 40, 41). Trace these two branches to their place of origin
from the N. facialis which place may be either under cover of the parotid
gland or a little distance anterior to it; if covered by the gland, remove
a small portion of the latter taking care not to cut the artery, nerve, or
vein which lie just dorsal to the nerve (PI. I, 32, 33, 42).

Before tracing the N. facialis farther, first dissect the auricular branch
of the second cervical nerve (Pl. I, 43). This large branch lies close to

4

the posterior border of the M. parotido-auricularis and extends approxi-
mately parallel to it. Trace the nerve to the external ear. Now dissect
the M. parotido-auricularis from the underlying parotid gland. Keep
close to the inner surface of the muscle to avoid cutting the very small
nerve, ramus colli, which for a part of its course lies between this muscle
and the gland (Pl. I, 44; Pl. I], 59). A small filament either from the
ramus colli or sometimes directly from the N. facialis is sent to the M.
parotido-auricularis.

Parotid gland and its duct.

Note the relations of the parotid gland to the mandible, the external
ear, the wing of the atlas and the great veins jugularis externa and maxil-
laris externa (Pls. I and II). Dissect the portion of the parotid duct which
extends, superficially, along the gland near its mandibular border noting the
several radicles which enter the duct from the gland. In the submaxillary
space the duct 1s covered by a thin aponeurosis which should be turned aside
or removed and the duct traced to the point where it leaves the submaxillary
space (Pl. I, 23). The remaining portion of the duct will be dissected later.
Note the relation of the submaxillary portion of the duct to the large V.
maxillaris externa (Pl. I, 23, 25).

The large V. auricularis posterior (Pl. I, 31; Pl. II, 36) will have been
partially exposed while tracing the auricular branch of the second cervical
nerve. ‘Trace this vein to its junction with the V. jugularis (Pl. II, 36).

The subglandular portion of the N. facialis should now be exposed but in
doing so care should be taken not to cut or break the V. temporalis super-
ficialis and the A. auricularis posterior (Pl. II, 37, 46) or any of the small
nerves given off from the N. facialis (Pl. II, 54, 59, 57, 58). With a tracer
or with the back of the scalpel, remove enough of the parotid gland to expose
clearly the nerve. The branch given off from the dorsal border of the
N. facialis immediately posterior to the large V. temporalis superficialis
is the N. auricularis anterior or auriculo-palpebraris (Pl. II, 54). This nerve
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 the stylohyoideus originate from the
N. facialis at the stylomastoid foramen (Pl. II, 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
(PIT, 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
posterior 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
foramen (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 II, 54).
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

6

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
mastoido-humeralis. 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.

Nn. digastricus, stylo-mandibularis and occipito-styloideus.

The nerve to the muscles digastricus and stylo-mandibularis originates
from the N. facialis close to the stylomastoid foramen, usually in common
with the nerve loop around the A. auricularis posterior, and passes directly
to the muscles (Pl. II, 57). No dissection other than the removal of the
parotid gland and the thin aponeurosis of the muscles is necessary to expose
this nerve. The very small nerve to the M. occipito-styloideus is some-
what difficult to find and should first be demonstrated to the student by the
instructor. It originates from the facialis close to or in common with the
preceding nerve. To expose this filament, transect the muscles mastoido-

7

humeralis and splenius, at the level of the V. auricularis posterior, and turn
aside their aponeurotic tendons; also turn aside or remove a portion of the
M. obliquus capitus anterior in order to expose fully the M. occipito-sty-
loideus. The latter muscle is covered by a thin aponeurosis which should be
carefully removed. The very small nerve lies on the surface of the muscle
just beneath the above mentioned aponeurosis, a little dorsal to the N. digas-
tricus. A magnifying glass is desirable to demonstrate this nerve satis-
factorily.

Nn. labiales.

These two large branches, labialis dorsalis and labialis ventralis (PI. I,
40, 41) are the direct continuations of the trunk of the N. facialis and supply
motor nerve fibres to the M. buccinator and all of the muscles of the lips and
nose. Students are not required to demonstrate the nerve supply to each
of these muscles but should keep clearly in mind that all of them are inner-
vated by the above mentioned branches of the N. facialis.

N. labialis ventralis.

This nerve gives off a large branch to the M. cutaneous faciei and the
skin (Pl. I, just below 36). Near the anterior border of the M. masseter
the N. labialis ventralis divides into several branches which supply the
muscles depressor labii inferioris, buccinator and the muscles of the lower
lip; the branches to the latter accompany the A. labialis inferior and are
covered by the M. depressor labii inferioris which should be transected near
its middle and turned aside.

N. labialis dorsalis.

The N. labialis dorsalis crosses the M. masseter dorsal to the N. labialis
ventralis. Anteriorly, the nerve is covered by the muscles zygomaticus,
levator naso-labialis and dilator naris lateralis (Pl. I). Transect and turn
aside these muscles and trace the nerve peripherally as far as possible. The
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.

8

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. Refer to 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
parotid 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 inferior. “

This artery originates from the A. maxillaris externa about 2 cm. ventral
to the M. depressor labii inferior (Pl. II, 40). 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 labii inferior, the inferior
molar glands and the lower lip and skin of this region.

A. labialis 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 (PI. I,
37; Pl. I, 41). It passes beneath the muscles zygomaticus, levator
nasolabialis and dilator naris lateralis all of which have previously been
turned aside. Trace the artery into the upper lip and demonstrate its
anastomosis 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.

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-

9

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. II, 31, 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 (PI. 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 facie. 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.) The dissection of the deep branches of the A. & V. transversa
faciei, already partially exposed, should now be completed. The artery
almost immediately divides into two branches of which the larger is distrib-
uted 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. pterygoideus internus. Trace the masseteric branch and its accompany-
ing artery as far as possible. The vein usually anastomoses with the

Io

V. buccinatoria. 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 Pl. II, but in doing this be
careful not to injure the large veins which lie beneath the muscle (PI. 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. II.

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
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, i. 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
attachment to the mandible and disarticulate and remove the condyle. Phe

at f

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 maxil'ary
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 carefully
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).

V. temporalis superficialis.

The V. temporalis superficialis is formed by the union of the veins
auricularis 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

12

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) V. 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. II, 28.
In tracing the latter do not cut the nerve which lies in close proximity to the
dorsal surface of the vein (PI. II, 65).

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 fibres of the smaller 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. ophthalmicus, the
N. maxillaris and the N. mandibularis. 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

13

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 foramen 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
foramen lacerum basis crani, and under cover of the M. pterygoideus
externus, 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. pterygoideus
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
mandible and upon emerging at the mental foramen it divides into several
branches known as the mental nerves, which are distributed to the chin and
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.

14

Gl. sublingualis.

Reflect the M. mylohyoideus and identify the sublingual salivary gland
(Pl. III, 35). Itis from 12 to 15 cm. 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. facialis. Demonstrate as much of the chorda tympani
as possible. At the anterior border of the M. pterygoideus internus 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. styloglossus deep
into the tongue. Dissect up the ventral edge of the sublingual gland and
turn it dorsally. Trace the nerve to the point where it dips between the
muscles styloglossus and genioglossus. Further dissection should be deferred
until after the N. sublingualis has been dissected. The N. lingualis gives off
several small branches to the region of the maxillary tuberosity (Pl. III).

(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
submaxillary 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

15

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
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 to clearly 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 PI. 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 (PI. III,

67.)

16

(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 partially 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 (PI. ITI,
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
osseous 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.|

17

(1) N. lacrimalis. Sensory (Pl. IV, 27).

This cons‘sts 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) N. 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 (Pls TVs 35).
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
between this membrane and the bone (PI. III). After passing through the
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 (BISW,<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 (PIV:
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 nasalfossa. 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 is distri-
buted 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).

18

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
meantime the three or four small nerves extending to the region of the
maxillary 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
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. E
(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 is 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.

19

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-mesial 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.
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 mesial or internal branch (see laboratory
specimen). The lateral branch runs along the inferior turbinated bone and
is distributed to its mucous membrane and to that of the middle and ventral
nasal meati. The mesial 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 towards the prenares. It lies near the ventral edge
of the nasal septum and is distributed to the mucous membrane of the septum
and, according to Ellenberger & Baum, 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
membrane 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).

20

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).

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 fami 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 be easily 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 les

21

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. rectus 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
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 lies 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 ganglii ciliaris). The sensory or long ciliary root of
the ganglion (radix longa ganglii 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.

N. abducens. VI. Motor.

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 ocul, 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.

22

N. acusticus. VIII. Sensory.

The apparent origin of this nerve is from the side of the medulla imme-
diately caudal to the N. facialis. 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. stylo-mandibularis 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 (PI. ITI, 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. thyreoideus.

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.

23

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 (PI. 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 (PI. III).

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) A. thyreoidea superior (PI. III, 37).

This is the largest collateral branch of the A. carotis communis. It
arises near the level of the thyreoid gland, bends over its cephalic end and
terminates by several branches in the ventral surface of the gland; several
large branches also enter the dorsal surface of the gland. It gives off a small
pharyngeal branch to the posterior part of the pharynx and a larger laryngeal
branch which passes between the cricoid and thyreoid cartilages to the interior
of the larynx.

(3) A. thyreoidea accessoria.

In this specimen, the artery arises from the carotis communis 5 cm. pos-
terior to the A. thyreoidea superior (10-12 cm. posterior to the trifurcation
of the carotid). It soon divides into three or four branches of which the
largest enters the posterior end of the thyreoid body; the other small branches
go to the muscles subscapulo-hyoideus, sterno-thyro-hyoideus and to the
trachea.

(4) <A. parotidea.

This artery is about the same size as the accessoria. It arises from the
carotid at the same level as the thyreoidea superior and divides into two
branches of which one goes to the parotid gland and to the muscles mastoido-

24

humeralis and rectus capitis anterior major; the other branch goes to the
submaxillary salivary gland and to the muscles sterno-mandibularis and
subscapulo-hyoideus and also supplies twigs to the cervical lymph gland.

A. occipitalis.

The origin of the A. occipitalis is from the carotis communis usually
immediately peripheral to that of the A. carotis interna (Pl. ITI, 38). Occa-
sionally, however, these two arteries arise by a common trunk of variable
length. The general course of the occipital artery is in nearly a direct line
to the alar foramen of the atlas. Beneath the wing of the atlas the artery
divides into two branches of which one passes through the alar foramen to
the region of the poll and the other through the foramen transversarium of
the atlas and anastomoses with the A. vertebralis. To expose the A. occipi-
talis turn aside the structures that cover the M. obliquus capitis posterior.
Cut the latter muscle along its attachment to the wing of the atlas, taking
care not to injure the arteries that pass through the foramen transversarium
and the foramen alare. Free the muscle from its attachment to the atlas
and the axis. Transect the M. obliquus capitis anterior close to its attach-
ment to the wing of the atlas and also close to the styloid process and the
crest of the occipital bone and turn it aside. _ Remove a portion of the wing
of the atlas in order fully to expose the artery.

Branches of the A. occipitalis.

(1) A small branch to the posterior extremity of the submaxillary
salivary gland (A. glandulae submaxillaris dorsalis).

(2) Small branches to the ventral recti muscles of the head and to the
parotid gland.

(3) The A. condyloidea is a very small branch which can be traced, at
present, for only a short distance. It divides into very small muscular and
meningeal branches. The former go to the muscles rectus capitis anterior
major and minor. The two very small meningeal branches enter the cranial
cavity by the foramen lacerum basis cranii and the hypoglossal foramen
respectively, and are distributed to the dura.

(4) A. meningea posterior.

This branch is much larger than any of the preceding branches. It runs
along the posterior edge of the styloid process of the occipital bone, passes
through the mastoid foramen (trace it only to this foramen) and is distri-
buted to the dura. Near the base of the styloid process it gives off a branch
to the region just posterior to the occipital tuberosity. :

25

(5) Ramus caudalis (retrograde).

This large branch leaves the A. occipitalis at nearly a right angle, passes
through the foramen transversarium of the atlas and anastomoses with the
A. vertebralis.

(6) Ramus occipitalis.

This large branch of the A. occipitalis passes through the alar foramen of
the atlas and supplies the muscles and skin in the region of the poll. In the
alar groove it gives off the A. cerebrospinalis which passes through the
intervertebral foramen of the atlas, penetrates the dura and divides into two
branches, ramus cerebralis and ramus spinalis. These two branches will
be demonstrated after removing the brain.

Pharyngeal lymph glands (PI. III, 31).

These glands he directly ventral to the M. stylohyoideus and are covered
laterally by the muscles stylo-mandibularis and digastricus. They often con-
sist of two groups; the larger and more compact group lies on the lateral
surface of the pharynx along the course of the A. carotis externa. The
smaller group, posterior or retropharyngeal lymph glands, are situated
between the posterior face of the pharynx and the eustachian or guttural air
sac. It consists of more or less isolated or scattered lymph nodules.

A. carotis interna (Pl. III, 39).

This artery is one of the three terminal branches of the carotis communis.
It extends to the foramen lacerum basis cranii through which it passes into
the cranial cavity. Its distribution to the brain will be demonstrated after
the removal of that organ.

A. carotis externa (Pl. III, 40).

The A. carotis externa is the largest of the three terminal branches of the
carotis communis. It crosses the lateral wall of the pharynx at the caudal
border of the eustachian or guttural air sac and is covered by the submaxil-
lary salivary gland, the muscles stylo-mandibularis, digastricus, stylohy-
oideus and the N. hypoglossus. Upon emerging from beneath these struc-
tures the artery passes more or less obliquely across the stylohyoid or great
cornu of the hyoid, and near its dorsal border divides into two terminal
branches: A. temporalis superficialis and A. maxillaris interna, the latter
being much the larger (Pl. III, 48, 51). The collateral branches of the carotis
externa are three in number, viz.: A. maxillaris externa, A. masseterica,
and A. auricularis posterior (Pl. III, 41, 46, 47).

26

(1) A. maxillaris externa.

The A. maxillaris externa rises from the carotis externa either on the inner
surface of the posterior belly of the M. digastricus or on the inner surface of
the M. stylohyoideus. In the first part of its course the artery crosses the
lateral wall of the pharynx nearly parallel to the stylohyoid bone and is
covered by the muscles digastricus and stylohyoideus. The N. hypoglossus
lies immediately ventral to the artery (Pl. III). After giving off the large
A. lingualis from its dorsal side (Pl. III, 43) the vessel inclines ventrally,
crosses the N. hypoglossus, the intermediate tendon of the digastricus where
the latter plays through the tendon of the stylohyoideus, the submaxillary
duct and often the end of the submaxillary gland itself, and enters the sub-
maxillary space near the posterior end of the submaxillary lymph gland. In
the submaxillary space the artery lies between the V. maxillaris externa and
the submaxillary lymph gland. The remaining or facial portion of the
A. maxillaris externa has already been dissected (p. 8). | Three collateral
branches arise from the A. maxillaris externa between its point of origin and
the anterior extremity of the submaxillary salivary gland, viz.: A.
palatina ascendens, A. lingualis and A. sublingualis. In addition to
these three collateral branches several small twigs are supplied to the M.
pterygoideus internus, the anterior extremity of the submaxillary salivary
gland and the pharyngeal lymph gland.

(a) A. palatina ascendens (PI. III, 42).

This artery arises from the dorsal side of the A. maxillaris externa 2 to 4
cm. from the A. carotis externa; sometimes, however, it arises in the angle
formed by the carotis externa and the maxillaris externa. It passes beneath
the stylohyoid bone, a short section of which should be removed, and is dis-
tributed to the lateral wall of the pharynx, the soft palate and the tonsil.

(b) A. lingualis (Pl. III, 43).

This large artery diverges from the maxillaris externa at the tip of the
thyroid cornu of the basihyoid, extends along the ventral edge of the stylo-
hyoid for a short distance and then dips under the M. hyoglossus. Before
exposing the artery first trace the large N. hypoglossus, which lies just ventral
to the A. maxillaris externa, across the lateral face of the M. hyoglossus.
Now push aside the M. styloglossus (PI. III, 12) in order more fully to expose
the M. hyoglossus (Pl. III, 13), and transect the latter muscle one to two
centimeters dorsal to the N. hypoglossus. Separate the M. hyoglossus from
the more deeply lying genioglossus and trace the artery to the tip of the
tongue. (Occasionally the A. lingualis lies on the superficial face of the
M. hyoglossus as in the specimen from which Plate III was made).

27

(c) A. sublingualis (Pl. ITI, 44).

This is a smaller vessel than the preceding. It arises from the maxillaris
externa at the anterior or cephalic extremity of the submaxillary salivary
gland, passes anteriorly on the inner face of the anterior belly of the M.
digastricus, and between the ramus of the mandible and the M. mylohyoideus
to near the middle of the latter muscle; here it pierces the mylohyoideus,
runs along the inner surface of the sublingual gland and terminates in the
mucous membrane of the anterior portion of the floor of the mouth. Just as
the artery passes through the mylohyoideus it gives off a branch, A. sub-
mentalis, which runs on the outer surface of the M. mylohyoideus towards
the lower lip and the chin. The A. sublingualis supplies small branches to
the mylohyoideus, digastricus, the sublingual gland and the submaxillary
lymph gland. Occasionally a branch of considerable size arises from the
maxillaris externa, near the place of origin of the A. sublingualis, crosses the
lower border of the mandible and is distributed to the M. masseter.

(2) A. masseterica.

This artery originates from the A. carotis externa at the dorsal border
of the M. stylohyoideus (Pl. III, 46). One or two centimeters from its
origin it divides into a superficial and a deep branch. The superficial branch
is distributed to the parotid gland and the M. masseter; the deep branch
to the muscles pterygoideus internus, stylomandibularis and the posterior
belly of the digastricus.

(3) A. auricularis posterior (continued).

The A. auricularis posterior arises at a very acute angle from the A.
carotis externa about one centimeter peripheral to the A. masseterica
(Pl. LI, 47). It extends dorsally towards the base of the ear and is
deeply covered by the parotid gland to which it sends numerous small
branches. The two superficial branches have already been dissected (p. 5).
The deep branch arises 1 to 2 cm. from the origin of the parent trunk, and
after giving off a small branch to the tympanum or middle ear, passes
between the external auditory canal and the mastoid process of the petrous
temporal. Transect the conchal cartilage and trace the artery as far as
possible.

A. temporalis superficialis.

This is the smaller of the two terminal branches of the A. carotis externa
(Pl. III, 48). After a course of I or 2 cm. it divides, under cover of the
parotid gland, into two branches, the A. auricularis anterior and the A.
transversa faciei (Pl. II, 47, 48; Pl. III, 49, 50).

28

(1) A. auricularis anterior.

The artery auricularis anterior is accompanied by the vein and nerve of
the same name and is deeply covered by the parotid gland to which it sends
numerous small twigs. The vessel runs posterior to the capsule of the
temporo-mandibular articulation and is distributed to the temporal and
auricular muscles and the overlying skin. It sends a small branch to the
inner surface of the conchal cartilage and also a branch which accompanies
the N. auriculo-palpebraris to the supraorbital foramen where it anastomoses
with the A. supraorbitalis.

(2) A. transversa faciei.
This artery has already been dissected. (See p. 9.)

A. maxillaris interna (Pl. III, 51).

The A. maxillaris interna is much the larger of the two terminal branches
of the carotis externa and is the direct continuation of it (Pl. III, 51). It
begins on the outer surface of the stylohyoid bone and extends in a tortuous
course to the pterygoid or alar foramen of the sphenoid bone, passes through
this foramen and the pterygo-palatine fossa, to the maxillary hiatus where it
is continued by the A. palatina major. For convenience, the artery may be
divided into three parts of which the first part, the longest and most tortuous,
extends from the stylohyoid bone to the pterygoid or alar foramen of the
sphenoid. The second part extends through the pterygoid or alar canal.
The third part extends from the anterior extremity of the pterygoid or alar
canal to the maxillary hiatus. The first part of the vessel describes an S-
shaped curve and is covered by the M. pterygoideus externus. Beneath this
muscle the artery is crossed superficially by the Nn. mylohyoideus, alveolaris
inferior, lingualis, pterygoidei, buccinatorius, and deeply by the chorda
tympani. Note the relation of the artery to the eustachian or guttural air
sac. The first part of the A. maxillaris interna gives off the following
branches:

(1) A. alveolaris inferior (Pl. III, 52).

This arises from the convexity of the first curve of the A. maxillaris
externa and with the vein and nerve of the same name passes through the
alveolar canal of the mandible. At the mental foramen the artery anasto-
moses with the A. labialis inferior and is continued to the lower lip as the
A. mentalis. The alveolaris inferior supplies twigs to the pterygoid muscles
and to the teeth and gums of the mandible; the branch to the canine and
incisor teeth accompanies the nerve that supplies these structures, as has
already been demonstrated.

29

(2) A. tympanica (Pl. III, 53).

This small vessel arises a little peripheral to the preceding but from the
opposite side of the A. maxillaris interna. It lies close to the common trunk
of the nerves alveolaris inferior and lingualis (at the side of the chorda
tympani) and enters the tympanum or middle ear.

(3) Aa. pterygoideae.

There are two or three of these small arteries. They arise from the
concavity of the second curve of the maxillaris interna (Pl. III, 55) and are
distributed to the pterygoid and tensor palati muscles.

(4) A. meningea media (Pl. III, 54).

The A. meningea media is a small artery which arises from the convexity
of the second curve of the maxillaris interna, nearly opposite the pterygoid
arteries and close to or even beneath the N. buccinatorius (Pl. III, 54).
Sometimes it arises in common with the A. temporalis profunda posterior.
It can be traced but a short distance. It enters the cranial cavity by the
foramen lacerum basis cranii and is distributed to the dura.

(5) A. temporalis profunda posterior (Pl. III, 56).

This vessel arises from the dorsal side of the A. maxillaris interna a little
before the latter enters the pterygoid or alar foramen. It is covered by the
M. temporalis to which it is mainly distributed. (For some distance the
artery accompanies the N. temporalis profunda posterior).

The second part of the A. maxillaris interna, i. e., the part in the pterygoid
canal, gives rise to two branches, A. temporalis profunda anterior and A.
ophthalmica. These two arteries commonly originate by a very short com-
mon trunk (Pl. V, 17).

(1) <A. temporalis profunda anterior (Pl. III, 57; Pl. IV, 14; Pl. V, 18).

This artery, as just mentioned, arises from the second part of the A.
maxillaris interna in common with the ophthalmica. It leaves the pterygoid
canal by the temporal foramen and is distributed to the M. temporalis and
the skin of the forehead.

(2) A. ophthalmica (Pl. V, 17).

This artery originates from the A. maxillaris interna within the pterygoid
canal in common with the A. temporalis profunda anterior. Upon emerging
from the canal it enters the apex of the periorbita. Beneath the M. rectus
dorsalis it makes a sharp curve of 180° and upon reaching the ethmoid fora-
men is continued by the A. ethmoidalis. (See laboratory specimen for the
distribution of this artery.) The branches of the A. ophthalmica are as
follows:

30

(a) A. lacrimalis (Pl. IV, 23).
This small artery accompanies the N. lacrimalis to the lacrimal gland and
upper eyelid.

(b) <A. supraorbitalis.

This vessel arises either from the A. temporalis profunda anterior or the
A. maxillaris interna. It pierces the periorbita between which and the
osseous wall of the orbit it extends directly to the supraorbital foramen
through which it passes and is distributed to the muscles orbicularis palpe-
brarum, corrugator supercilii and the skin of the forehead.

(c) Rami musculares.
The numerous muscular branches that supply the muscles of the eye.

(d) Aa. ciliares.

The numerous small ciliary arteries arise from the ophthalmica and its
muscular branches. They are distributed to the ciliary body, the iris and
the choroid coat of the eye.

(e) A. centralis retinae.
This is a small artery which supplies the retina.

(f) A. ethmoidalis. (Trace this only to the ethmoid foramen).

The A. ethmoidalis is the continuation of the ophthalmica. It passes
through the ethmoid foramen into the cranial cavity and divides into
meningeal and nasal branches. The meningeal branch is distributed to the
dura and anastomoses with the A. corporis callosi. The nasal branch passes
through the cribriform plate into the nasal fossaand is distributed to the nasal
mucous membrane.

The third part of the A. maxillaris interna is shown in Pl. IV. It extends
from the anterior opening of the pterygoid canal to the maxillary hiatus. It
gives off the following branches:

(a) A. buccinatoria (Pl. IV, 19; Pl. II, 50; and Pl. III, 58).

The A. buccinatoria arises from the ventral side of the parent trunk soon
after the latter emerges from the pterygoid canal. It crosses the maxillary
tuberosity with the N. buccinatorius, and is distributed to the dorsal molar
glands and the muscles pterygoidei and buccinator. Near its origin the
A. buccinatoria gives off a long slender branch (PI. IV, 16) to the large mass
of orbital fatty tissue in the temporal fossa, posterior to the periorbita.

31

(b) <A. infraorbitalis (Pl. IV, 17).

The A. infraorbitalis arises from the dorsal side of the maxillaris interna
(Pl. IV, 17). It extends to the infraorbital canal, through which it passes,
and continues to the canine and incisor teeth through the small osseous
canal (canalis alveolaris incisivus) in the maxillary and premaxillary bones.
Before entering the infraorbital canal it gives off the A. orbitalis (Pl. IV, 18),
which extends between the periorbita and the anterior wall of the orbit to
the inner or nasal canthus of the eye and is distributed to the lower eyelid,
the M. obliquus ventralis and the lacrimal sac. Within the infraorbital
canal the A. infraorbitalis gives off small branches to the teeth and, at the
infraorbital foramen, a branch of variable size which anastomoses with
either the A. labialis dorsalis or the A. lateralis nasi.

(c) A. palatina minor.

This is a very small vessel which arises from the maxillaris interna, passes
through the groove at the inner side of the maxillary tuberosity and is dis-
tributed to the soft palate (Pl. IV, 20). The N. palatinus posterior and the
palatine vein also pass through this groove with the artery.

(d) A. sphenopalatina (Pl. IV, 21; Pl. V, 24).

This vessel arises from the A. maxillaris interna at the extreme anterior
part of the pterygo-palatine fossa, close to the orifice of the palatine canal,
and passes through the spheno-palatine foramen into the nasal fossa where
it divides into two branches. (See laboratory specimen). One of these
branches is distributed to the mucous membrane of the nasal septum and
the other to the mucous membrane of the inferior turbinal, the inferior
meatus, the posterior nares and the maxillary and frontal sinuses.

(e) A. palatina major.

This artery is the direct continuation of the maxillaris interna. It passes
through the palatine canal and groove with the N. palatinus anterior. At
the incisive foramen it anastomoses with its fellow of the opposite side.
From the arch formed by this anastomosis a branch passes through the
incisive foramen and anastomoses with the dorsal labial arteries.

N. glossopharyngeus. IX. Mixed.

The N. glossopharyngeus originates, superficially, from the side of the
medulla. It passes through the foramen lacerum basis cranii with the Nn.
vagus and accessorius (Pl. III, 78). The nerve is readily found at any point
along its course between the stylohyoid or great cornu of the hyoid and the
A. maxillaris externa (Pl. III, 84). It should not be mistaken for the much
larger N. hypoglossus which runs parallel to it but which lies on the ventral
side of the artery. Expose, as follows, the proximal portion of the nerve.

32

With a chisel cut the styloid process of the occipital bone close to its base
(Pl. III, 3) and reflect it, together with the portions of muscles attached to it,
onto the stylohyoid. Trace the N. glossopharyngeus towards the base of the
skull, noting its relation to the A. carotis externa and to the great N. hypo-
glossus, with which it is in close contact in this part of its course. Near the
base of the skull these two nerves, together with the trunk of the vagus and
sympathetic, are bound together by connective tissue into one large cord
which is partially surrounded by a fold of the eustachian or guttural air sac.
In exposing the nerves of this region it is not necessary to cut or tear the thin
wall of this sac; it may be simply pushed from around the nerves with the
handle of the scalpel. At the base of the skull note the enlargement of the
N. glossopharyngeus, the ganglion petrosum (Pl. III, 79). A small nerve,
N. tympanicus, originates from the antero-lateral face of the ganglion and
extends dorsally, closely applied to the surface of the ganglion, into the
tympanum or middle ear. Not infrequently some difficulty is experienced
in demonstrating this small nerve; by using’a magnifier, however, it can
usually be seen without much difficulty (Pl. III, 80). The next branch of
the N. glossopharyngeus is given off anywhere from 2 to 6 cm. before the
main trunk crosses the A.carotis externa. This branch passes directly to the
carotid nerve plexus at the trifurcation of the A. carotis communis. Very
frequently this branch of the glossopharyngeus is joined by a branch from the
superior cervical ganglion (Pl. III, 93) of the sympathetic nerve shortly
before reaching the plexus. Asthe N. glossopharyngeus crosses the mesial
surface of the A. carotis externa it divides into two nearly equal branches,
ramus pharyngeus and ramus lingualis.

(a) Ramus pharyngeus (PI. III, 82).

Trace this branch to the place where it crosses, at a right angle, the
stylohyoid bone and the M. stylopharyngeus. Note the small filament to
the M. stylopharyngeus (PI. III, 83); this filament may originate from either
the pharyngeal or the lingual branch of the N. glossopharyngeus. Opposite
the place where the nerve crosses the stylohyoid and the M. stylopharyngeus,
remove a section of the bone as shown in Plate III. Near the dorsal edge
of the M. stylopharyngeus the nerve turns sharply and divides into numerous
small branches which intermix with one of the pharyngeal branches of the
vagus, as will be seen later, to form the pharyngeal plexus. The numerous
branches of this plexus are distributed to the pharyngeal muscles and mucous
membrane.

(b) Ramus lingualis (Pl. III, 84).
This branch of the N. glossopharyngeus is somewhat larger than the
pharyngeal branch and lies between the stylohyoid bone and the A. maxillaris

33

externa as already mentioned. Turn aside the stylohyoid bone and trace the
nerve peripherally. It gives several small branches to the isthmus of the
fauces and the tonsil and terminates in the mucous membrane of the pos-
terior third of the dorsum of the tongue.

N. vagus. X. Mixed.

The superficial origin of the vagus is from the ventro-lateral side of the
medulla. It passes through the foramen lacerum basis cranii in company
with the N. accessorius or the eleventh cranial nerve. The two nerves
appear as a single trunk for a distance of 2 to 5 cm. from the base of the skull;
they then separate and the great N. hypoglossus passes between them (PI.
III, 92), the vagus being mesial and the N. accessorius lateral to the hypoglos-
sus (Pl. III, 85). Trace the vagus for some distance along the course of the
carotis interna and carotis communis noting that near the trifurcation of the
carotis communis the vagus becomes closely united to the N. sympathicus
(I III, 95).

(1) Pharyngeal branch of the N. vagus (Pl. III, 86).

The pharyngeal branch of the vagus is given off opposite the superior
cervical ganglion of the sympathetic (Pl. III, 86, 93) and soon divides into
two nearly equal branches. Upon drawing the carotid artery, the vagus and
the sympathetic nerves somewhat ventrally, one of these branches may be
traced to its place of distribution to the pharyngeal muscles and the pharyn-
geal extremity of the oesophagus. The other branch of the pharyngeal
nerve passes deeply between the eustachian or guttural air sacs, and is more
difficult to follow; however, by pushing aside the walls of the sacs the nerve
may be traced to the dorso-lateral wall of the pharynx near to the insertion
of the M. stylopharyngeus (Pl. III, 10), where it divides into numerous
branches some of which intermix with the pharyngeal branch of the N.
glossopharyngeus, the two together forming the pharyngeal plexus, as
already mentioned.

(2) N. laryngeus superior (Pl. III, 87). Sensory.

The large N. laryngeus superior arises from the vagus about 6 cm. from
the point where the vagus and hypoglossus cross each other (PI. III, 87).
At the place where the laryngeus superior leaves the trunk of the vagus is an
indistinctly marked network sometimes called the ganglion nodosum. The
N. laryngeus superior crosses the mesial face of the Aa. carotis externa and
interna, near their origin, and enters the larynx through the foramen near
the cephalic border of the thyreoid cartilage. The nerve is distributed to the
mucous membrane of the larynx, the floor of the pharynx and the entrance to
the oesophagus. A very small branch, sometimes called the N. laryngeus

34

externus or medius, is given off either from the plexiform enlargement of the
vagus (ganglion nodosum) or more commonly from the N. laryngeus superior
and extends directly to the M. cricothyroideus; it also supplies a small fila-
ment to the M. cricopharyngeus.

(3) N. laryngeus inferior or recurrens.

The origin and course of the N. laryngeus inferior can not be seen until
the thoracic portion of the vagus is dissected. Its distribution to the muscles
of the larynx will be taken up later.

N. accessorius. XI. Motor.

This nerve has its origin in part from the medulla and in part from the
cervical portion of the spinal cord. The portion which originates from the
spinal cord begins between the sixth and seventh spinal nerves and extends
cephalad, within the spinal canal, along the lateral face of the spinal cord
between the dorsal and ventral roots of the first six spinal nerves. In this
ascending course it gradually increases in size as it at intervals receives
additional filaments from the spinal cord. After entering the cranial cavity
the nerve receives some filaments from the medulla. The N. accessorius
accompanies the vagus to the foramen lacerum basis cranii and for a short
distance from the base of the skull, as already noted (Pl. III, 90). After
leaving the vagus the nerve passes across the lateral surface of the eustachian
or guttural air sac and the ventral surface of the wing of the atlas and finally
gains the dorsal border of the M. mastoido-humeralis along which it extends
nearly the entire length of the neck. The distribution of this portion of the
nerve is principally to the thoracic portion of the muscle trapezius; oneor
more small branches, however, are supplied to the cervical portion of the
trapezius and to the muscle mastoido-humeralis. Shortly after crossing the
A. occipitalis the N. accessorius sends off a large branch to the muscle sterno-
mandibularis (Pl. III, 91). In its course along the neck the nerve is joined
by branches from the ventral divisions of the first six cervical nerves.

N. hypoglossus. XII. Motor.

The superficial origin of the N. hypoglossus is from the medulla. It
passes through the hypoglossal foramen and between the vagus and acces-
sorius (Pl. III, 92). The hypoglossus crosses the lateral face of the A. carotis
externa, at the place of origin of the A. maxillaris externa, and then extends
along the ventral side of the latter vessel as far as to the ceratohyoid of the
hyoid; from this point it extends between the muscles mylohyoideus and
hyoglossus to about opposite the tip of the lingual prolongation of the basi-
hyoid, a distance of 8 to 10 cm., where it divides into a superficial and a deep
branch. The smaller superficial branch supplies the muscles styloglossus

35

and hyoglossus. The larger deep branch of the hypoglossus crosses the
ventral edge of the M. hyoglossus and extends obliquely between this muscle
and the M. genio-hyoglossus toward the tip of the tongue. In this inter-
muscular course the nerve divides into many branches which are distributed
to the muscles of the tongue. Near the point where the N. hypoglossus
divides into superficial and deep branches it gives off a small filament to the
M. geniohyoideus. The N. hypoglossus communicates with the ventral
division of the first cervical nerve by a small threadlike ramus which joins the
hypoglossus just before the latter crosses the A. maxillaris externa or at any
point intermediate to this and the base of the skull (PI. ITI, nerve just below
31). The N. hypoglossus also gives off one or more small filaments which
join the carotid plexus.

N. laryngeus inferior (continued).

The N. laryngeus inferior, of the left side, arises from the vagus within the
thorax. It recurves around the arch of the aorta and in the first part of its
course lies on the ventro-lateral face of the trachea; nearer the larynx the
nerve lies on the dorso-lateral face of the trachea. In order to trace the
terminal portion of the nerve, the pharyngeal muscles of the left side (or
right side as the case may be) must be transected and turned aside. Near
the posterior end of the M. crico-arytenoideus posterior is given off the
branch to this muscle, entering at its deep face and near the lateral border of
the muscle. Carefully trace the main trunk of the N. laryngeus inferior to
the point where it passes beneath the thyreoid cartilage. Disarticulate the
posterior cornu of the thyreoid from the cricoid and abduct the former suffi-
ciently toexpose the muscles crico-arytenoideus lateralis and thyro-arytenoi-
deus. Near the middle of the lateral border of the M. crico-arytenoideus
posterior a small branch is given off to the M. arytenoideus. This branch
passes beneath the M. crico-arytenoideus posterior which should be tran-
sected and turned aside. Beneath the thyreoid cartilage the laryngeal nerve
terminates in branches which supply the muscles crico-arytenoideus lateralis,
thyro-arytenoideus and also one or more branches that anastomose with the
N. laryngeus superior. All of these respective branches should be traced to
their proper muscles. The N. laryngeus inferior of the right side recurves
around the A. dorso-cervicalis and is similarly distributed to the muscles of
the right side of the larynx.

PLATE I

. splenialis.

. mastoido-humeralis.

. sterno-mandibularis.

. subscapulo-hyoideus.

. auricularis inferior or parotido-auricularis.

and 7. Mm. cervico-auriculares.

. zygomatico-auricularis.

. parieto-auricularis.

. masseter.

. orbicularis oculi.

. corrugator supercilii.

. lacrimalis (or malaris).

. levator naso labialis.

. levator labii superioris proprius.

. dilator naris lateralis.

. zygomaticus.

. buccinator.

. cutaneous faciei (facial panniculus).
. depressor labii inferioris.

. orbicularis oris.

Gl.

parotis.

Ductus parotideus.

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. jugularis.

. maxillaris externa.
. labialis communis.
. lateralis nasi.

dorsalis nasi.

. angularis ocult.
masseterica. (This vein and artery are incorrectly represented as lying on the surface of the M.
masseter; they are really embedded in the muscle.)

auricularis posterior.
transversa faciei.

transversa faciei.
masseterica.

maxillaris externa or facialis.

. labialis inferior.
. labialis superior.
. lateralis nasi.

. angularis oculi.

. labialis superior.
. labialis inferior.
. transversus faciei (a branch of the N. temporalis superficialis).

Second spinal nerve.
Ramus colli, a branch of the N. facialis.

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PLATE II

M. splenius.

M. mastoido-humeralis.

M. sterno-mandibularis.

M. subscapulo-hyoideus.

M. cervico-auricularis.

M. stylomandibularis.

M. masseter (partially removed).

M. orbicularis oculi.

M. corrugator superciulii, turned aside.

M. malaris or lacrimalis.

M. levator nasolabialis.

M. levator labii superioris proprius.

M. dilator naris lateralis.

M. zygomaticus.

M. buccinator, showing cut edge.

M. orbicularis oris.

M. cutaneous faciei (facial panniculus).

M. depressor labii inferioris.

Gl. parotis.

Ductus parotideus.

Gl. molares superior.

Gl. molares inferior.

V. jugularis.

V. maxillaris externa.

V. labialis communis.

V. lablialis superior.

V. labialis inferior.

Communicating branch between V. buccina-
toria and the Vv. labiales.

V. buccinatoria.

V. alveolaris.

V. transversa faciei.

V. lateralis nasi.

V. dorsalis nasi.

V. angularis oculi.

V. masseterica.

V. auricularis posterior.

V. temporalis superficialis.

maxillaris interna.

maxillaris externa.

. labialis inferior.

labialis superior.

lateralis nasi.

dorsalis nasi.

angularis oculi.

masseterica.

auricularis posterior.

auricularis anterior.

transversa faciei.

. alveolaris inferior. (inferior dental).

. buccinatoria.

. facialis.

- auricularis posterior.

. auricularis medius (or internus).

. auricularis anterior.

Plexus auricularis anterior.

Small nerve from the N. temporalis super-
ficialis.

N. (or ramus) digastricus. -

Nerve loop around the A. auricularis posterior.

Ramus colli.

N. temporalis superficialis.
5th cranial nerve).

N. labialis superior.

N. labialis inferior.

N. massetericus.

N. alveolaris inferior (inferior dental) or (N.
alveolaris mandibulae).

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. N. mentalis.

N. buccinatorius.

Branches of the N. supraorbitalis.
N. infraorbitalis.

N. nasilis dorsalis.

N. nasalis anterior.

N. labialis dorsalis.

Second spinal nerve.

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PLATE III

Supraorbital pocess.
Zygomatic process.
Styloid process of occipital.
Cut surface of malar bone.
Stylohyoid. (A portion has been removed).
Mandible.
M. temporalis.
M. pterygoideus externus.
M. pterygoideus internus.
M. Stylopharyngeus.
M. stylohyoideus.
M. styloglossus.
M. hyoglossus, partially reflected.
M. genioglossus.
M. geniohyoideus.
M. mylohyoideus.
M. digastricus (anterior belly).
M. rectus capitus anterior major.
M. crico-pharyngeus.
M. thyro-pharyngeus.
M. hyo-pharyngeus.
M. hyo-thyroideus.
M. cerato-hyoideus.
M. crico-thyroideus.
M. sterno-mandibularis.
M. subscapulo-hyoideus.
M. sterno-thyroideus.
Trachea.
Oesophagus.
Gl. thyreoidea.
Pharyngeal lymph glands.
Submaxillary lymph gland.
Submaxillary salivary gland.
Ductus submaxillaris.
Sublingual gland (greater portion has been re-
moved).
Gl. lacrimalis.
. carotis communis.
. thyreoidea.
. occipitalis.
carotis interna.
carotis externa.
maxillaris externa.
palatina ascendens.
lingualis.
sublingualis.
mazxillaris externa.
masseterica.
auricularis posterior.
. temporalis superficialis.
. transversa faciei.
. auricularis anterior.

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. maxillaris interna.

. alveolaris inferior.

tympanica.

meningea media.

pterygoieda.

temporalis profunda posterior.

temporalis profunda anterior.

buccinatoria.

transversa faciei.

alveolaris.

mandibularis.

massetericus.

n. temporales profundi posterior.

buccinatorius.

temporalis profundus anterior.

maxillaris.

pterygoideus externus.

pterygoideus internus.

lingualis.

sublingualis.

alveolaris inferior.

mylohyoideus.

chorda tympani.

temporalis superficialis.

facialis.

digastricus.

. Stylohoideus.

. glossopharyngeus.

Ganglion petrosum.

N. tympanicus.

Branch to carotid plexus.

Ramus pharyngeus.

Branch to the M. stylopharyngeus.

Ramus lingualis.

N. vagus.

Ramus pharyngeus.

N. laryngeus superior.

N. laryngeus externus.

Combined trunks of the Nn. vagus and synpa-
thicus.

N. accessorius.

Branch to M. sterno-mandibularis.

N. hypoglossus.

Superior cervical ganglion of the sympathetic

nerve.

N. sympathicus, accompanying the internal
carotid.

N. sympathicus.

Plexus caroticus.

Eustachian pouch, or air sac (guttural pouch).

Branch of first spinal nerve.

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PLATE IV

Cut surface of the supraorbital process.

Frontal sinus.

Cut surface of the zygomatic process of the temporal.
Cut surface of the malar.

Palpebrae.

Gl. lacrimalis.

M. rectus dorsalis or superior.

. levator palpebrae dorsalis or superior. ‘ .
. rectus lateralis.

. rectus ventralis or inferior.

. obliquus ventralis or inferior.

. retractor oculi or bulbi.

A. maxillaris interna.

A. temporalis profunda anterior.

A. supraorbitalis.

Small artery to the mass of adipose tissue in the temporal fossa.

A. infraorbitalis.

A. orbitalis or malaris.

A. buccinatoria.

A. palatina posterior.

A. sphenopalatina.

Muscular branch of the A. ophthalmica.

A. lacrimalis.

N. trochlearis.

N. supraorbitalis or frontalis.

N. nasociliaris (palpebronasal).

N. lacrimalis.

N. orbitalis or zygomaticus.

Branch of the N. oculomotorius to the M. obliquus ventralis.
N. mazxillaris.

N. sphenopalatinus.

N. palatinus anterior or major.

N. palatinus posterior or minor.

Cut edge of the periorbita or ocular sheath.

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PLATE V

Cut surface of supraorbital process.
Frontal sinus.
Cut surface of the zygomtic process of the temporal.
Cut surface of the malar.
Palpebrae.
Gl. lacrimalis (Somewhat reflected).
M. rectus dorsalis or superior.
M. levator palpebrae dorsalis or superior.
M. rectus lateralis.
M. rectus ventralis or inferior.
M. rectus medialis.
M. obliquus dorsalis or superior.
M. obliquus ventralis or inferior.
M. retractor oculi or bulbi. <
Cut edge of sphenoid.
A. Maxillaris interna.
A. ophthalmica.
A. temporalis profunda anterior.
A. supraorbitalis or frontalis.
Small artery to the mass of adipose tissue in the temporal fossa.
. infraorbitalis.
orbitalis or malaris.
buccinatoria.
sphenopalatina.
Maxillaris, cut and one end turned aside.
lacrimalis, cut and turned aside.
supraorbitalis or frontalis.
. nasociliaris or palpebronasal.
ethmoidalis.
infratrochlearis.
trochlearis.
Sensory root of Gang. ciliare.
and 34. N. oculomotorious, dorsal and ventral branches.
Small branch from the N. oculomotorious to the M. levator palpebrae dorsalis.
N. abducens.
N. orbitalis or zygomaticus (the peripheral portion has been removed).
Ganglion ciliaris.
Nn. ciliares.
N. opticus.
N. sphenopalatinus.
Ganglion sphenopalitinum showing many small nerves leaving it.
N. palatinus anterior or major.
N. palatinus posterior or minor.
Cut edge of the periorbita or ocular sheath.

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