Chapter V: Muscles of the Leg and Foot (19)

Section is cut about 1.5 cm. to the right of the median plane. _M_,
Medulla oblongata; _P_, pons; _P.c._ (above _M_), chorioid plexus of
fourth ventricle; _C.m._, central white matter (corpus medullare) of
cerebellum and of cerebrum; _P.c._ (in front of _P_), cerebral
peduncle; _H_, hippocampus; _V_, lateral ventricle; _T_, thalamus;
_N.c._, caudate nucleus; _C.i._, internal capsule; _N.l._,
lenticular nucleus; _B.o._, olfactory bulb.
]

The =corpus striatum=[202] is the great basal ganglion of the hemisphere. It is situated in front of the thalamus and the cerebral peduncle, and its anterior rounded end appears on the base of the hemisphere at the trigonum olfactorium. It is composed of two masses of gray matter, the caudate and lenticular nuclei, separated incompletely by tracts of white matter which are known collectively as the internal capsule. The =caudate nucleus= (Nucleus caudatus) is the dorso-medial and larger of the two gray masses; it has been seen in the examination of the floor of the lateral ventricle. The =lenticular nucleus= (Nucleus lentiformis) lies ventro-laterally, over the trigonum olfactorium and the fossa transversa. It is related externally to a layer of white matter termed the =external capsule=, which separates it from a stratum of gray substance known as the =claustrum=. The two nuclei are fused in front, and further back they are connected by strands of gray matter which intersect the internal capsule.

The =amygdaloid nucleus= (Nucleus amygdalæ) (Fig. 506) is an ovoid mass of gray matter situated external to the ventral horn of the lateral ventricle and below the posterior part of the lenticular nucleus. Some fibers of the stria terminalis are connected with it.

The =internal capsule= (Capsula interna) is a broad band of white matter situated between the thalamus and caudate nucleus internally and the lenticular nucleus externally. A sagittal section through the brain shows that it is in great part directly continuous with the basis or ventral part of the cerebral peduncle. It contains most of the so-called =projection fibers= of the hemisphere, which connect the cerebral cortex with nuclei of other and more posterior parts of the brain. When the fibers of the internal capsule are traced forward it is evident that they spread out in all directions to reach the cerebral cortex. This arrangement, in which the fibers of the corpus callosum participate, is termed the =corona radiata=.

The internal capsule also contains fibers which connect the corpus
striatum with the thalamus. These are termed the thalamo-striate and
strio-thalamic fibers respectively, according to the direction in
which they conduct impulses.

The fibers of the stria terminalis connect the amygdaloid nucleus with
the septum pellucidum and trigonum olfactorium. It is therefore
probably part of the complex connections between the primary and
secondary olfactory centers.

THE CRANIAL NERVES

The =cranial= or =cerebral nerves= (Nn. cerebrales) comprise twelve pairs which are designated from before backward numerically and by name. Their number, names, and functional characters are given in the subjoined table:

I. Olfactory Sensory (Small)
II. Optic Sensory (Sight)
III. Oculomotor Motor
IV. Trochlear Motor
V. Trigeminal Mixed
VI. Abducent Motor
VII. Facial Mixed
VIII. Auditory Sensory (Hearing and Equilibration)
IX. Glosso-pharyngeal Mixed
X. Vagus or Pneumogastric Mixed
XI. Spinal accessory Motor
XII. Hypoglossal Motor

THE FIRST OR OLFACTORY NERVE

The =olfactory nerve= (N. olfactorius) is peculiar in that its fibers are not aggregated to form a trunk, but are connected in small bundles with the olfactory bulb. They are non-medullated, and are the central processes of the olfactory cells which are situated in the olfactory region of the mucous membrane of the nasal cavity. This region is distinguished by its brown color and comprises most of the lateral mass of the ethmoid, a small adjacent area of the superior turbinal, and the corresponding surface of the septum nasi. The nerve-bundles are inclosed in sheaths derived from the membranes of the brain and pass through the foramina of the cribriform plate to join the convex surface of the olfactory bulb. Some fibers come from the vomero-nasal organ of Jacobson.

THE SECOND OR OPTIC NERVE

The =optic nerve= (N. opticus) is composed of fibers which are the central processes of the ganglion cells of the retina. The fibers converge within the eyeball to the optic papilla, where they are collected into a round trunk, the optic nerve. The nerve thus formed pierces the chorioid and sclera, emerges from the posterior part of the eyeball, and passes backward and inward to the optic foramen. After traversing the latter it decussates with its fellow of the opposite side to form the optic chiasma or commissure. In the orbit the nerve is slightly flexuous and is embedded in the fat behind the eyeball and surrounded by the retractor oculi muscle. Its intraosseous part is an inch or more (ca. 3 cm.) long. The =sheath= of the nerve is formed by prolongations of the membranes of the brain, and includes continuations of the subdural and subarachnoid spaces.

The greater part of the fibers of the optic nerve cross in the chiasma
to the tract of the opposite side. In the tract the fibers proceed to
(1) the internal geniculate body, (2) the posterior part of the
thalamus, and (3) the anterior quadrigeminal body (indirectly). The
fibers which go to the internal geniculate body appear to belong to
Gudden’s commissure and to be nonvisual in function. The visual
fibers, which come from the outer part of the retina of the same side
and the inner part of the retina of the opposite side, terminate about
cells in the anterior quadrigeminal body and the part of the thalamus
which corresponds to the pulvinar and external geniculate body of man.
From the cells of the former fibers pass to the nuclei of the motor
nerves of the eyeball, and complete the reflex arc. Fibers proceed
from the cells of the thalamus to the visual area of the cortex in the
occipital part of the hemisphere.

THE THIRD OR OCULOMOTOR NERVE

The =oculomotor nerve= (N. oculomotorius) arises by several radicles from the basal surface of the cerebral peduncle, a little lateral to the interpeduncular furrow. It turns sharply outward and forward, crosses over the cavernous sinus, and continues above the maxillary nerve and in company with the ophthalmic nerve to the foramen lacerum orbitale. It emerges through the foramen with the latter nerve and the abducens and divides into two branches. The =superior branch= is short and divides into twigs which supply the rectus superior, retractor, and levator palpebræ superioris. The =inferior branch= (Figs. 438, 439) is larger and much longer. It supplies the motor fibers to the ciliary ganglion (which lies directly on this branch in the horse) and short branches to the rectus internus and rectus inferior, and continues forward on the latter to end in the inferior oblique muscle.

The deep origin of the fibers of the oculomotor nerve is in the
oculomotor nucleus situated in the gray matter of the floor of the
cerebral aqueduct in the region of the anterior corpora quadrigemina.

THE FOURTH OR TROCHLEAR NERVE

The =trochlear= or pathetic (N. trochlearis) is the smallest of the cranial nerves. It arises from the anterior cerebellar peduncle just behind the corpora quadrigemina, curves outward and forward, pierces the tentorium cerebelli, and passes forward along the outer border of the maxillary nerve (Figs. 504, 505). It emerges from the cranium through a small foramen immediately above the foramen lacerum orbitale or through the latter and passes forward along the inner wall of the orbit to end in the posterior part of the superior oblique muscle of the eyeball (Fig. 439).

The fibers of the fourth nerve spring from a nucleus in the gray
matter of the floor of the cerebral aqueduct behind the oculomotor
nucleus. The fibers run backward in the tegmentum, then turn upward
and inward and undergo total decussation with those of the opposite
nerve in the anterior part of the anterior medullary velum. In
addition to this peculiarity it is the only nerve which is connected
with the dorsal aspect of the brain.

THE FIFTH, TRIGEMINAL, OR TRIFACIAL NERVE

The =trigeminal nerve= (N. trigeminus) is the largest of the cranial series. It is connected with the lateral part of the pons by a large =sensory root= and a smaller =motor root= (Fig. 499).

The =sensory root= (Portio major) extends forward through a notch on the lower part of the petrosal crest and widens out to join the semilunar ganglion.

The =semilunar= (or Gasserian) =ganglion= (Ganglion semilunare) is a crescent-shaped mass of nerve-fibers and cells which overlies the antero-external part of the foramen lacerum basis cranii, and is partly embedded in the dense fibrous tissue which occupies the foramen except where vessels and nerves pass through. Its long axis, which is about an inch (2.5 cm.) in length, is directed forward and inward and its convex anterior face gives rise to the ophthalmic, the maxillary, and the sensory part of the mandibular division of the nerve. The surface of the ganglion is irregularly striated. It is connected by filaments with the adjacent carotid plexus of the sympathetic, and sends delicate twigs to the dura mater.

The fibers of the sensory root arise from the ganglion as axones of
the ganglion cells, and the fibers of the nerves which extend
peripherally from the ganglion are dendrites of the cells. The sensory
root-fibers enter the tegmentum of the pons and divide into anterior
and posterior branches, which terminate about the cells of the sensory
nucleus of termination of the trigeminus. This nucleus extends from
the pons to the sixth cervical segment of the spinal cord (Dexler).
The posterior branches of the fibers are collected into a compact
bundle, the spinal tract or root of the trigeminus, which lies lateral
to the substantia gelatinosa in the medulla. The central connections
of the sensory part of the trigeminus are very extensive. The most
important paths are: (1) Axones of cells of the sensory nucleus and
the substantia gelatinosa pass chiefly as arcuate fibers across the
raphé to the thalamus, whence impulses are transmitted by
thalamo-cortical fibers to the cerebral cortex. In ungulates a
distinct tract extends from the anterior part of the sensory nucleus
to the thalamus of the same side (Wallenberg). It is probable that
collaterals of the arcuate fibers go to the motor nuclei of the fifth,
seventh, ninth, and tenth cranial nerves. (2) Axones of cells of the
sensory nucleus enter the posterior cerebellar peduncle of the same
side and reach the cerebellar cortex. (3) Collaterals are distributed
to the nuclei of origin of the hypoglossal and of the motor part of
the trigeminal and facial nerves.

The =motor root= (Portio minor) extends forward beneath the sensory root and the semilunar ganglion and is incorporated with the mandibular division of the nerve. Its fibers arise chiefly from the so-called masticatory nucleus, which is situated in the pons near the inner face of the sensory nucleus; a few of these fibers come from the nucleus of the opposite side and cross in the raphé. Other fibers, which constitute the mesencephalic root, arise from cells in the outer part of the central gray matter of the mid-brain.

It is evident from the foregoing statements that the trigeminus has essentially the same arrangement as a typical spinal nerve. It divides into three branches.

I. The =ophthalmic nerve= (N. ophthalmicus) (Figs. 438, 439, 440) is purely sensory and is the smallest of the three branches of the trigeminus. It arises from the inner part of the front of the semilunar ganglion, passes forward along the outer side of the cavernous sinus, and is blended with the maxillary nerve for some distance. It enters the foramen lacerum orbitale with the third and sixth nerves and divides into three branches.

1. The =lacrimal nerve= (N. lacrimalis) runs forward on the rectus superior and the levator palpebræ superioris and ramifies chiefly in the lacrimal gland and the upper eyelid. A branch (Ramus zygomatico-temporalis) exchanges twigs with the zygomatic branch of the maxillary nerve, perforates the periorbita, and emerges from the orbital fossa behind the supraorbital process; it forms a plexus with branches of the auriculo-palpebral and frontal nerves, and ramifies in the skin of the temporal region.

2. The =frontal nerve= (N. frontalis), also termed the supraorbital, runs forward almost parallel with the superior oblique muscle, at first within, then outside of, the periorbita. It passes through the supraorbital foramen with the artery of like name and ramifies in the skin of the forehead and upper eyelid, forming a plexus with the lacrimal and auriculo-palpebral nerves. It divides into three branches.

3. The =naso-ciliary nerve= (N. naso-ciliaris), also termed the palpebro-nasal, runs forward along the inner side of the optic nerve between parts of the retractor muscle and divides into two branches. Of these the =ethmoidal nerve= (N. ethmoidalis) is the continuation of the parent trunk. It accompanies the ethmoidal artery through the foramen of like name into the cranial cavity and crosses the lower part of the ethmoidal fossa. Leaving the cranium through an opening in the cribriform plate close to the crista galli, it enters the nasal cavity and ramifies in the mucous membrane of the septum nasi and the superior turbinal. The =infratrochlear nerve= (N. infratrochlearis) runs forward to the inner canthus and ramifies in the skin in this region; it detaches twigs to the conjunctiva and caruncula lacrimalis, and a long branch which supplies the third eyelid and the lacrimal ducts and sac. The naso-ciliary nerve furnishes the =sensory= or =long root= (Radix longa) of the ciliary ganglion.

The =ciliary ganglion= is placed on the inferior branch of the oculomotor nerve. It is usually not larger than a millet-seed, and is best found by following the nerve to the inferior oblique muscle back to its origin. The ganglion receives (_a_) =sensory fibers= from the naso-ciliary nerve; (_b_) =motor fibers= from the oculomotor nerve; and (_c_) =sympathetic fibers= from the sphenopalatine plexus. It detaches filaments which unite with twigs from the ophthalmic and maxillary nerves and from the sphenopalatine ganglion to form the ciliary plexus. From the latter emanate five to eight delicate =short ciliary nerves= (Nn. ciliares breves), which pursue a somewhat flexuous course along the optic nerve, pierce the sclera near the entrance of that nerve, and run forward between the sclera and chorioidea to the circumference of the iris. Here the branches of adjacent nerves anastomose to form a circular plexus (Plexus gangliosus ciliaris), from which filaments go to the ciliary body, iris, and cornea.

The circular fibers of the iris and the ciliary muscle are innervated
by fibers derived from the oculomotor nerve, the radial fibers of the
iris by the sympathetic.

II. The =maxillary nerve= (N. maxillaris), also termed the superior maxillary, is purely sensory and is much larger than the ophthalmic. It extends forward from the semilunar ganglion in the middle cranial fossa in the large groove on the root of the temporal wing of the sphenoid. It is related internally to the cavernous sinus and superiorly to the ophthalmic nerve, with which it is blended for some distance. It emerges through the foramen rotundum, passes forward in the pterygo-palatine fossa above the internal maxillary artery and embedded in fat, and is continued in the infraorbital canal as the infraorbital nerve (Fig. 439). Its branches are as follows:

1. The =zygomatic nerve= (N. zygomaticus s. subcutaneus malæ), also termed the orbital branch, arises before the maxillary nerve reaches the pterygo-palatine fossa (Figs. 438, 439, 514). It pierces the periorbita and divides into two or three delicate branches which pass along the surface of the external straight muscle to the external canthus and ramify chiefly in the lower lid and the adjacent skin. Anastomoses are formed with branches of the lacrimal nerve.

2. The =sphenopalatine nerve= (N. sphenopalatinus) is given off in the pterygo-palatine fossa from the lower border of the maxillary nerve (Fig. 439). It is broad and flat and forms a plexus in which several small =sphenopalatine ganglia= are interposed. It divides into posterior nasal, and greater and lesser palatine nerves. (1) The =posterior nasal nerve= (N. nasalis aboralis) passes through the sphenopalatine foramen, in which it bears one or more minute ganglia, enters the nasal cavity, and divides into internal and external branches (Figs. 440, 464). The internal branch (N. septi narium) runs forward in the submucous tissue of the lower part of the septum nasi, gives twigs to the mucous membrane here and to the vomero-nasal organ (of Jacobson), passes through the palatine cleft and ramifies in the anterior part of the hard palate. The external branch (Ramus lateralis) ramifies in the mucous membrane of the inferior turbinal and the middle and inferior meatus nasi. (2) The =greater= or =anterior palatine nerve= (N. palatinus major s. anterior) (Figs. 438, 439) is the largest of the three branches. It runs forward in the palatine canal and groove and ramifies in the hard palate and gums. It also supplies twigs to the soft palate, and gives off branches which pass through the accessory palatine foramina to supply the mucous membrane of the inferior meatus.

The branches of the two nerves anastomose in the hard palate and form
a plexus about the branches of the palatine arteries.

FIG. 514.—DISSECTION OF HEAD OF HORSE.

The masseter and superficial muscles and the parotid gland are in
great part removed. _a_, _a_, Levator labii superioris proprius;
_b_, _b_, levator nasolabialis; _c_, dilatator naris inferior; _d_,
buccinator; _e_, common mass of buccinator and depressor labii
inferioris; _f_, depressor labii inferioris; _g_, masseter; _h_,
orbicularis oculi; _i_, temporalis; _k_, occipito-hyoideus; _k′_,
stylo-maxillaris; _l_, sterno-cephalicus; _l′_, tendon of same; _m_,
omo-hyoideus; _n_, crico-pharyngeus; _o_, mastoid tendon of
mastoido-humeralis; _p_, splenius; _q_, inferior buccal and labial
glands; _r_, superior buccal glands; _s_, remnant of parotid gland;
_t_, submaxillary gland; _u_, anterior cervical (subparotid) lymph
glands; _v_, probe passed into diverticulum nasi; _w_, cornu of alar
cartilage; _x_, internal palpebral ligament; _y_, wing of atlas;
_z_, scutiform cartilage of ear; _1_, external nasal nerve; _2_,
anterior nasal nerve; _3_, superior labial nerve; _4_, anterior part
of superior buccal nerve; _5_, buccinator nerve; _6_, _6′_, inferior
alveolar nerve; _6″_, mental nerve-continuation of _6_; _7_,
masseteric nerve; _8_, facial nerve (cut); _9_, superficial temporal
nerve; _10_, anastomosis between _9_ and _8_; _11_, internal
auricular nerve; _12_, posterior auricular nerve; _13_, digastric
nerve; _14_, cervical branch of facial nerve (cut); _15_,
auriculo-palpebral nerve; _16_, lacrimal nerve; _17_, frontal nerve;
_18_, infratrochlear nerve; _19_, n. zygomaticus s. subcutaneus
malæ; _20_, spinal accessory nerve; _21_, ventral branch of spinal
accessory nerve (to sterno-cephalicus); _22_, ventral end branch of
first cervical nerve; _23_, thyro-laryngeal artery; _24_, internal
maxillary artery; _25_, masseteric artery; _26_, great (posterior)
auricular artery; _27_, external branch of _26_; _28_, deep
auricular artery; _29_, superficial temporal artery; _30_,
transverse facial artery; _31_, facial artery; _32_, inferior labial
artery; _33_, superior labial artery; _34_, lateral nasal artery;
_35_, dorsal nasal artery; _36_, angular artery of eye; _37_, labial
twigs of palato-labial artery—left uncolored by oversight; _38_,
branch of buccinator artery; _39_, buccinator vein; _40_, vena
reflexa; _41_, _42_, jugular vein; _43_, external maxillary vein;
_44_, inferior cerebral vein; _45_, stump of great auricular vein;
_46_, ramus of mandible; _47_, facial crest; _48_, zygomatic arch;
_49_, parotid duct. (After Ellenberger-Baum, Top. Anat. d. Pferdes.)
]

(3) The =lesser= or =posterior palatine nerve= (N. palatinus minor s. posterior), also termed the staphyline, is much the smallest of the three branches (Figs. 438, 439). It passes downward and forward with the palatine vein in the groove at the inner side of the tuber maxillare and ramifies in the soft palate.

The sphenopalatine ganglia and plexus (Fig. 515) lie on the
perpendicular part of the palate bone and the pterygoid process under
cover of the maxillary nerve. The afferent fibers of the plexus and
ganglia come chiefly from the branches of the sphenopalatine nerve and
the nerve of the pterygoid canal. Interspersed in these are several
minute ganglia and one or more larger ones. The =nerve of the
pterygoid canal= or =Vidian nerve= (N. canalis pterygoidei) is formed
by the union of sympathetic fibers with the superficial petrosal
branch of the facial nerve. It passes forward at first between the
Eustachian tube and the sphenoid bone, enters the canal between the
pterygoid bone and process, and joins the posterior part of the
plexus. It is probable that it furnishes the motor fibers to the
levator palati and palatinus muscles. Efferent filaments go to the
periorbita and the ophthalmic vessels, and others accompany the
branches of the maxillary nerve, around which they have a plexiform
arrangement.

3. The =infraorbital nerve= (N. infraorbitalis) is the continuation of the maxillary trunk. It traverses the infraorbital canal, emerges through the infraorbital foramen, and divides into nasal and superior labial branches. Along its course it gives off =superior alveolar= or =dental branches= (Rami alveolares maxillæ), which supply the teeth, alveolar periosteum, and gums.

The delicate posterior alveolar branches are given off in the
pterygo-palatine fossa, pass through small foramina in the tuber
maxillare, and supply the posterior molar teeth and the maxillary
sinus. The middle alveolar branches are given off in the infraorbital
canal, and constitute the chief nerve-supply to the cheek teeth and
the maxillary sinus. The anterior or incisor branch runs forward in
the anterior alveolar or incisor canal and supplies branches to the
canine and incisor teeth. The foregoing unite with each other to form
the superior dental plexus, from which the dental and gingival
branches are given off.

The =external nasal branches= (Rami nasales externi), two or three in number, accompany the levator labii superioris proprius and ramify in the dorsum nasi and the nasal diverticulum.

The large =anterior nasal branch= (Ramus nasalis anterior) passes over the nasal process of the premaxilla under cover of the dilatator naris inferior, gives branches to the nasal mucous membrane, and terminates in the skin of the upper lip.

The =superior labial branch= (Ramus labialis dorsalis) is the largest of the terminals of the infraorbital nerve. It passes downward and forward under the levator nasolabialis and, after supplying the skin of the anterior part of the cheek, forms a rich terminal ramification in the skin and mucous membrane of the upper lip. It anastomoses with the superior buccal branch of the facial nerve.

III. The =mandibular nerve= (N. mandibularis), also termed the inferior maxillary branch, is formed by the union of two roots; of these the large sensory root comes from the semilunar ganglion, and the small motor root is the pars minor of the trigeminus. It emerges from the cranium through the oval notch of the foramen lacerum, between the temporal wing of the sphenoid bone and the muscular process of the petrous temporal, and gives off the following branches:

1. The =masseteric nerve= (N. massetericus) (Figs. 437, 515) passes outward through the sigmoid notch of the mandible and enters the deep face of the masseter muscle, in which it ramifies.

2. The =deep temporal nerves= (Nn. temporales profundi) (Fig. 437), two or three in number, arise by a common trunk with the masseteric. They supply the temporal muscle.

3. The =buccinator nerve= (N. buccinatorius) passes obliquely forward through the anterior part of the external pterygoid muscle, then between the internal pterygoid and the tuber maxillare (Fig. 514). It continues forward in the submucous tissue of the cheek along the lower border of the buccinator and divides into branches which ramify in the mucous membrane and glands of the lips in the vicinity of the commissure. It supplies small branches to the external pterygoid and temporal muscles and detaches numerous collateral twigs to the mucous membrane of the cheek and to the buccal glands. It also communicates with the inferior buccal branch of the facial nerve.

4. The =pterygoid nerve= (N. pterygoideus) arises in common with the preceding, passes forward on the guttural pouch, and divides into branches for the pterygoid muscles (Fig. 515).

The =otic ganglion= (G. oticum) is situated near the origin of the pterygoid and buccinator nerves, and is related internally to the tensor palati and the Eustachian tube. It receives motor fibers from the pterygoid nerve and sensory fibers by the small superficial petrosal nerve from the tympanic plexus, through which communications are made with the facial and glosso-pharyngeal nerves. Sympathetic fibers are derived from the plexus on the internal maxillary artery. Efferent filaments go to the tensor palati, tensor tympani, and pterygoid muscles, and to the Eustachian tube.

The ganglion is small and somewhat difficult to demonstrate. In many
cases it is replaced by a number of minute ganglia interspersed in a
fine plexus.

5. The =superficial temporal nerve= (N. temporalis superficialis) (Figs. 437, 514, 515) runs outward across the pterygoideus externus, passes between the parotid gland and the neck of the ramus of the mandible, turns around the latter, and divides into two branches. The upper branch (Ramus transversus faciei) accompanies the transverse facial vessels and ramifies in the skin of the cheek. The larger inferior branch unites with the inferior buccal division of the facial nerve.

FIG. 515.—DEEP DISSECTION OF BASE OF CRANIUM, VIEWED FROM THE RIGHT
AND BELOW.

The tympanic cavity is opened and the paramastoid process is sawn off.
_a_, Occipital condyle; _b_, body of sphenoid; _c_, external
auditory meatus (part removed); _d_, malleus; _e_, incus; _1_, stump
of ophthalmic nerve; _2_, maxillary nerve (cut off); _3_,
sphenopalatine plexus; _4_, Vidian nerve; _4′_, deep petrosal nerve;
_4″_, branch to tympanic plexus; _4‴_, superficial petrosal nerve;
_5_, superficial temporal nerve (cut off); _6_, masseteric nerve
(cut off); _7_, mandibular nerve (raised); _8_, lingual nerve (cut
off); _9_, pterygoid nerve (cut); _10_, nerve to tensor tympani;
_11_, otic ganglion; _12_, facial nerve; _13_, stapedial nerve;
_14_, chorda tympani; _15_, glosso-pharyngeal nerve (cut); _16_,
tympanic nerve; _17_, vagus (cut off); _18_, auricular branch of
vagus; _19_, spinal accessory nerve (cut off); _20_, hypoglossal
nerve (cut off); _21_, sympathetic nerve (cut off); _22_, internal
carotid artery. (After Ellenberger, in Leisering’s Atlas.)
]

Before its division the nerve gives off twigs to the guttural pouch, the parotid gland, the external ear, and the skin of the external auditory meatus and the membrana tympani. Branches from it concur with filaments from the cervical branch of the facial nerve in the formation of the auricular plexus.

6. The =inferior alveolar= or =dental nerve= (N. alveolaris mandibulæ) (Figs. 436, 437, 514) arises with the lingual by a common trunk which passes forward at first on the external pterygoid muscle, then inclines ventrally between the internal pterygoid and the ramus of the mandible. The lingual and alveolar separate at an acute angle, and the latter enters the mandibular foramen and courses in the canal within the ramus (Fig. 516). Emerging at the mental foramen, it terminates by dividing into six to eight inferior labial and mental branches, which ramify in the lower lip and chin. Before entering the bone, the nerve detaches the =mylo-hyoid nerve= (N. mylo-hyoideus), which runs downward and forward between the ramus and the mylo-hyoid muscle; it supplies that muscle, the anterior belly of the digastricus, and the skin of the anterior part of the submaxillary space. The dental and gingival branches detached from the nerve within the mandible are arranged like the corresponding nerves of the upper jaw.

7. The =lingual nerve= (N. lingualis) arises by a common trunk with the inferior alveolar or dental nerve (Figs. 436, 437). After separating from the latter it runs downward and forward, lying at first between the ramus of the mandible and the internal pterygoid muscle, then on the inner face of the mylo-hyoid. On reaching the root of the tongue it divides into superficial and deep branches. The =superficial branch= (Ramus superficialis) runs forward on the stylo-glossus and accompanies the submaxillary duct on the deep face of the sublingual gland. It supplies the mucous membrane of the tongue and the floor of the mouth. At the root of the tongue it gives off a recurrent branch to the isthmus faucium, which communicates with the lingual branch of the glosso-pharyngeal nerve. The larger =deep branch= (Ramus profundus) turns around the lower edge of the hyo-glossus, passes upward and forward between that muscle and the genio-glossus, and continues forward on the latter to the tip of the tongue. It gives branches to the mucous membrane and the fungiform papillæ of the tongue, and anastomoses with branches of the hypoglossal nerve and with the superficial branch. Minute ganglia occur on the finer branches of the lingual nerve. The =chorda tympani= branch of the facial joins the lingual nerve at the origin of the latter and is incorporated with it in its distribution to the tongue.

FIG. 516.—PART OF BRANCH OF LOWER JAW OF HORSE, INTERNAL VIEW.

The bone has been removed to show the vessels and nerves. _1_, _1′_,
Inferior alveolar or dental nerve; _2_, _2_, branches to cheek teeth
and gums; _2′_, branch to canine and incisor teeth; _3_, _3′_,
inferior alveolar or dental artery; _4_, satellite vein. (After
Leisering’s Atlas.)
]

THE SIXTH OR ABDUCENT NERVE

The =abducent nerve= (N. abducens) emerges from the brain behind the pons and just external to the pyramid (Fig. 499). It passes forward across the pons, pierces the dura mater, and accompanies the third and ophthalmic nerves, below which it emerges through the foramen lacerum orbitale. In the orbit it divides into two branches; the larger of these enters the external rectus, the smaller supplies the superior and external parts of the retractor muscle of the eyeball. Within the cranium it receives filaments from the carotid plexus of the sympathetic.

The fibers of the abducent nerve are axones of the large multipolar
cells of the abducent nucleus which is situated beneath the eminentia
teres of the floor of the fourth ventricle. The nucleus lies within
the loop formed by the fibers of origin of the facial nerve. It is
connected with (_a_) the anterior olive; (_b_) the oculomotor nucleus
of the opposite side; (_c_) the motor area of the cerebral cortex by
means of the pyramidal tract of the opposite side.

THE SEVENTH OR FACIAL NERVE

The =facial nerve= (N. facialis) has its superficial origin at the lateral part of the corpus trapezoideum, immediately behind the pons (Fig. 499). It passes outward in front of the eighth nerve and enters the internal auditory meatus. At the bottom of the meatus the two nerves part company, the facial coursing in the facial canal of the petrous temporal bone. The canal and nerve are at first directed outward between the vestibule and the cochlea, then curve backward and downward in the posterior wall of the tympanum to end at the stylo-mastoid foramen. The bend formed by the nerve is called the =knee= (Geniculum n. facialis) and bears at its highest point the round =geniculate ganglion= (G. geniculi).

The nerve consists of two parts, motor and sensory. The =motor part=
constitutes the bulk of the nerve. Its deep origin is from the cells
of the =facial nucleus=, which is situated in the medulla above the
facial tubercle. On leaving the nucleus the root-fibers pass upward
and inward, incline forward close to the median plane, and then bend
sharply downward to the point of emergence. The highest point of the
bend is subjacent to the gray matter of the eminentia teres in the
floor of the fourth ventricle, and the abducent nucleus lies in the
concavity of the curve. The small =sensory part= (N. intermedius)
consists of axones of cells of the geniculate ganglion, which is
interposed on the facial nerve as it bends downward in the facial
canal. The fibers of this part after entering the medulla, pass to the
nucleus of termination which it shares with the ninth and tenth
nerves. The peripheral fibers from the geniculate ganglion constitute
the chorda tympani.

After its emergence through the stylo-mastoid foramen (Fig. 514) the nerve passes downward, forward, and outward on the guttural pouch under cover of the parotid gland, and crosses between the origin of the superficial temporal and internal maxillary arteries internally and the superficial temporal vein externally. It then crosses the posterior border of the ramus of the mandible ventral to the transverse facial artery and about an inch and a half (ca. 3.5 to 4 cm.) below the articulation of the jaw. Emerging from beneath the parotid gland upon the masseter muscle, it receives the lower branch of the superficial temporal nerve, and divides into superior and inferior buccal branches. The following collateral branches are given off, the first five being detached within the facial canal, and the others between the stylo-mastoid foramen and the border of the jaw.

1. The =great superficial petrosal nerve= (N. petrosus superficialis major) arises from the geniculate ganglion.[203] It passes through the petrosal canal, contributes a filament to the tympanic plexus, receives the great deep petrosal nerve from the carotid plexus of the sympathetic, emerges through the foramen lacerum, and is continued as the Vidian nerve to the sphenopalatine plexus and ganglia (Fig. 515).

2. A delicate branch (R. anastomoticus cum plexu tympanico) emerges from the geniculate ganglion and unites with a filament issuing from the tympanic plexus to form the =small superficial petrosal nerve= (N. petrosus superficialis minor); this ends in the otic ganglion.

3. The =stapedial nerve= (N. stapedius) (Fig. 515) is a short filament detached from the facial nerve as it turns down in the facial canal. It innervates the stapedius muscle.

4. The =chorda tympani= (Fig. 515) is a small nerve which arises a little below the preceding and pursues a recurrent course in a small canal in the mastoid part of the temporal bone to reach the tympanic cavity. It traverses the latter, passing between the handle of the malleus and the long branch of the incus. Emerging through the petro-tympanic fissure, the nerve passes downward and forward, crosses beneath the internal maxillary artery, and joins the lingual nerve. It sends twigs to the submaxillary and sublingual glands, and through its incorporation with the lingual nerve furnishes fibers to the mucous membrane of the anterior two-thirds of the tongue which are believed to mediate the sense of taste.

5. Anastomotic filaments unite with the auricular branch of the vagus near the stylo-mastoid foramen.

6. The =posterior auricular nerve= (N. auricularis posterior) arises from the facial at its emergence from the facial canal (Fig. 514). It runs upward and backward with the posterior auricular artery under cover of the parotid gland and supplies the posterior auricular muscles and the skin of the convex surface of the external ear. It anastomoses with branches of the first and second cervical nerves.

7. The =internal auricular nerve= (N. auricularis internus) springs from the facial close to or in common with the preceding (Fig. 514). It ascends in the parotid gland just behind the styloid process of the conchal cartilage, passes through an opening in the cartilage, and ramifies in the skin of the concave surface of the ear.

8. The =digastric branch= (R. digastricus) (Fig. 514) arises from the facial below the auricular nerves. Its branches innervate the posterior belly of the digastricus, the stylo-hyoideus, and the occipito-hyoideus. At its origin it gives off a small branch which forms a loop around the great auricular artery or its posterior branch and rejoins the trunk.

9. The =auriculo-palpebral nerve= (N. auriculo-palpebralis) (Fig. 514) arises from the upper edge of the facial near the posterior border of the ramus. It ascends in the parotid gland behind the superficial temporal artery, and terminates in anterior auricular and temporal branches. The =anterior auricular branches= form with branches of the trigeminus the =anterior auricular plexus=. They innervate the anterior auricular and parotido-auricularis muscles. The =temporal branch= runs forward and inward over the temporal muscle to the inner canthus of the eye, forms a plexus with the terminal branches of the ophthalmic nerve, and is distributed to the orbicularis oculi, corrugator supercilii, and levator nasolabialis.

10. The =cervical branch= (R. colli) (Fig. 435) arises from the ventral border of the facial opposite to the preceding nerve. It emerges obliquely through the parotid gland, passes downward and backward on or near the jugular vein, and anastomoses with the cutaneous branches of the cervical nerves. It gives branches to the parotido-auricularis and the cervical panniculus. In its course along the neck the nerve is reinforced by twigs from the cutaneous branches of the second to the sixth cervical nerves.

11. Small branches are detached to the guttural pouch and the parotid gland. The latter (Rami parotidei) concur with branches of the superficial temporal nerve in forming the =parotid plexus=.

The facial nerve usually terminates after a short course on the surface of the masseter by dividing into two buccal branches (Figs. 435, 461).

1. The =superior buccal nerve= (N. buccalis dorsalis) passes forward on the upper part of the masseter, dips under the zygomaticus, and continues along the lower border of the dilatator naris lateralis. It then runs under the last-named muscle and anastomoses with branches of the infraorbital nerve, and is distributed to the muscles of the cheek, upper lip, and nostril.

2. The =inferior buccal nerve= (N. buccalis ventralis) crosses the masseter obliquely and continues forward along the depressor labii inferioris. It is connected by variable anastomotic branches with the superior nerve. It gives collateral branches to the panniculus, buccinator, and depressor labii inferioris, and ramifies with the terminal branches of the inferior alveolar nerve in the lower lip.

The buccal nerves are subject to much variation in regard to their
course, anastomoses, and relations to the sensory components derived
from the superficial temporal nerve. Their distribution is constant.
The point at which the branch of the superficial temporal nerve joins
the facial is variable.

THE EIGHTH OR AUDITORY NERVE

The =auditory nerve= (N. acusticus) is connected with the lateral aspect of the medulla just behind and external to the facial (Fig. 499). It has two roots, vestibular and cochlear (Radix vestibularis et cochlearis).

The auditory nerve consists of two distinct parts which might well be
regarded as separate nerves. The cochlear part mediates the sense of
hearing, while the vestibular part is not auditory in function, but is
concerned in the sense of the position of the body and the mechanism
of equilibration.

The nerve passes outward to the internal auditory meatus, which it enters behind the facial nerve. In the meatus it divides into two nerves, of which the upper is the vestibular and the lower is the cochlear nerve.

1. The =vestibular nerve= (N. vestibuli) is distributed to the utriculus, the sacculus, and to the ampullæ of the semicircular canals, of the internal ear. In the internal auditory meatus the nerve is connected by filaments with the geniculate ganglion of the facial nerve. At the bottom of the meatus it bears the =vestibular ganglion= (G. vestibulare), from the cells of which the fibers of the nerve arise.

2. The =cochlear nerve= (N. cochleæ) detaches a filament to the sacculus, passes through the lamina cribrosa to the labyrinth, and is distributed to the organ of Corti in the cochlea.

The fibers of the vestibular nerve arise from the vestibular ganglion
as central processes (axones) of the bipolar cells of the ganglion.
The peripheral processes (dendrites) of the cells form arborizations
about the deep ends of the hair cells of the maculæ and cristæ
acusticæ of the utriculus, sacculus, and semicircular canals. The
fibers enter the medulla, pass between the restiform body and the
spinal tract of the trigeminus, and spread out to end in the
vestibular nucleus in the floor of the fourth ventricle. Among the
central connections of the vestibular nerve are: (1) fibers which
connect its nucleus with centers in the cerebellum (chiefly of the
opposite side); (2) the vestibulo-spinal tract, which conveys impulses
to the motor cells of the ventral columns of the spinal cord; (3)
fibers which connect the nucleus with those of the abducent nerve of
the same side, the third and fourth nerves, and the motor part of the
trigeminus of both sides.

The fibers of the cochlear nerve are the central processes of the
bipolar cells of the spiral ganglion of the cochlea. The peripheral
processes of these cells end in relation to the hair cells of the
organ of Corti. Some of the nerve-fibers enter the ventral cochlear
nucleus in the medulla close to the superficial origin of the nerve;
others end in the dorsal nucleus of the tuberculum acusticum at the
lateral angle of the floor of the fourth ventricle. From the ventral
nucleus fibers pass in the corpus trapezoideum to the anterior olivary
nucleus of the same and of the opposite side. Thence tracts pass to
the nuclei of the motor nerves of the eye, and through the lateral
fillet to the posterior quadrigeminal body and the internal geniculate
body. The axones of the cells of the dorsal nucleus pass largely (as
the striæ acusticæ) over the restiform body and across the floor of
the fourth ventricle toward the median plane. They then turn
ventrally, cross to the opposite side, and are continued by the
lateral fillet. From the mid-brain a tract proceeds to the cortex of
the temporal lobe of the hemisphere.

THE NINTH OR GLOSSO-PHARYNGEAL NERVE

The =glosso-pharyngeal nerve= (N. glossopharyngeus) is attached to the anterior part of the lateral aspect of the medulla by several filaments (Fig. 499). The root-bundles enter the furrow ventral to the restiform body; they are separated by a short interval from the origin of the facial nerve, but are not marked off behind from the roots of the vagus. The bundles converge laterally to form a nerve which perforates the dura mater and emerges through the foramen lacerum posterius just in front of the tenth nerve (Fig. 515). As it issues from the cranium the nerve bears a considerable ovoid gray enlargement, the =petrous ganglion= (G. petrosum).[204] It then curves downward and forward over the guttural pouch and behind the great cornu of the hyoid bone, crosses the deep face of the external carotid artery, and divides into pharyngeal and lingual branches (Fig. 437). The collateral branches are as follows:

1. The =tympanic nerve= (N. tympanicus) (Fig. 515) arises from the petrous ganglion and passes upward between the petrous and tympanic parts of the temporal bone to reach the cavity of the tympanum. Here it breaks up into branches to form, along with branches from the carotid plexus of the sympathetic, the =tympanic plexus=. From the plexus branches pass to the mucous membrane of the tympanum and the Eustachian tube. The continuation of the nerve issues from the plexus and unites with a filament from the geniculate ganglion of the facial to form the small superficial petrosal nerve; this runs forward and ends in the otic ganglion.

Filaments also connect the petrous ganglion with the jugular ganglion
of the vagus nerve and with the superior cervical ganglion of the
sympathetic.

2. A considerable branch runs backward on the guttural pouch, contributes filaments to the pharyngeal plexus, and concurs with twigs from the vagus and the sympathetic in forming the carotid plexus on the terminal part of the carotid artery and on its chief branches. In this plexus is the small ganglion intercaroticum.

The =pharyngeal branch= (R. pharyngeus) (Fig. 437) is the smaller of the two terminal branches. It runs forward across the deep face of the great cornu of the hyoid bone and concurs with the pharyngeal branches of the vagus and with sympathetic filaments in forming the pharyngeal plexus; from this branches pass to the muscles and mucous membrane of the pharynx.

The =lingual branch= (R. lingualis) is the continuation of the trunk (Fig. 437). It runs along the posterior border of the great cornu of the hyoid bone in front of the external maxillary artery and dips under the hyo-glossus muscle. It gives collateral branches to the soft palate, isthmus faucium, and tonsil, and ends in the mucous membrane of the posterior part of the tongue, where it supplies gustatory fibers to the vallate papillæ. A considerable branch unites with a twig from the lingual nerve.

The glosso-pharyngeal is a mixed nerve, containing both motor and
sensory fibers. The latter constitute the bulk of the nerve and
include those which mediate the special sense of taste. They are
processes of the cells of the petrous ganglion. The central processes
of the ganglion cells enter the medulla, pass upward and inward
through the formatio reticularis, and end in the nucleus of
termination in the floor of the fourth ventricle. The motor fibers
arise from dorsal and ventral efferent nuclei in the medulla. The
glosso-pharyngeal shares these nuclei with the vagus and has
practically the same central connections as that nerve (_q. v._).

THE TENTH, VAGUS, OR PNEUMOGASTRIC NERVE

The =vagus= or =pneumogastric= (N. vagus) is the longest and most widely distributed of the cranial nerves; it is also remarkable for the connections which it forms with adjacent nerves and with the sympathetic. It is attached to the lateral aspect of the medulla by several filaments which are in series with those of the ninth nerve in front and the eleventh nerve behind (Fig. 499). The bundles converge to form a trunk which passes outward, pierces the dura mater, and emerges from the cranium through the foramen lacerum posterius (Fig. 515). In the foramen the nerve bears on its lateral aspect the elongated flattened =jugular ganglion= (G. jugulare).

The ganglion communicates with (_a_) the tympanic nerve, (_b_) the
petrous ganglion of the ninth nerve, (_c_) the spinal accessory, and
(_d_) the hypoglossal. It also gives off the =auricular branch= (R.
auricularis), which runs forward below the petrous ganglion and passes
through a small canal in the petrous temporal bone to gain the facial
canal. Here it gives filaments to the facial and emerges with that
nerve through the stylo-mastoid foramen. It ascends behind the
external auditory meatus, dips under the rotator longus muscle, and
passes through a foramen in the conchal cartilage to ramify in the
integument which lines the meatus and the adjacent part of the ear.

Beyond the ganglion the vagus runs backward and downward with the spinal accessory in a fold of the guttural pouch (Fig. 437). Then the two nerves separate, allowing the hypoglossal to pass between them, and the vagus descends with the internal carotid artery and crosses the inner face of the origin of the occipital artery. Here it is joined by the cervical trunk of the sympathetic, and the two nerves continue along the dorsal aspect of the common carotid artery in a common sheath (Fig. 433). At the root of the neck the vagus separates from the sympathetic, and from this point backward the relations of the right and left vagi differ somewhat and must be described separately.

FIG. 517.—CROSS-SECTION OF NECK OF HORSE, PASSING THROUGH POSTERIOR
PART OF ATLAS.

The head and neck were extended. _1_, Dorsal arch of atlas; _2_,
odontoid process; _3_, odontoid ligament; _4_, vertebral sinuses;
_5_, dura mater; _6_, spinal cord; _7_, vertebral artery; _8_, wing
of atlas; _9_, atlanto-axial joint cavity; _10_, œsophagus; _11_,
_11_, recurrent nerves; _12_, _12_, ventral branches of spinal
accessory nerves. By an oversight the obliquus cap. post. (above
wing of atlas) is unmarked.
]

The =right vagus= (Fig. 429) enters the thorax in the angle of divergence of the right brachial artery and the truncus bicaroticus. It then passes backward and slightly upward, crossing obliquely the outer surface of the brachiocephalic artery and the right face of the trachea. Reaching the dorsal surface of the latter near the bifurcation, it divides into dorsal and ventral branches.

The =left vagus= (Fig. 428) enters the thorax on the ventral face of the œsophagus, crosses obliquely under the left brachial artery, and passes back on the external surface of that vessel in company with a large cardiac nerve.[205] Separating from the latter, the vagus continues backward on the left face of the aorta, inclines to the upper surface of the left bronchus, and divides into dorsal and ventral branches.

The dorsal and ventral branches unite with the corresponding branches of the opposite nerve, thus forming =dorsal= and =ventral œsophageal trunks= (Truncus (œsophageus dorsalis, ventralis). These run backward in the posterior mediastinum, above and below the œsophagus respectively, and enter the abdominal cavity through the hiatus œsophageus; they supply branches to the œsophagus and anastomose with each other. The dorsal trunk receives the major part of its fibers from the right vagus. After entering the abdomen it passes to the left of the cardia, gives branches to the visceral surface of the stomach, and ends in the cœliac and subsidiary plexuses. The ventral trunk passes to the lesser curvature of the stomach and ramifies on the parietal surface of the stomach; it forms here the anterior gastric plexus, from which branches are supplied also to the first part of the duodenum and to the liver.

The collateral branches of the vagus are as follows:

1. The =pharyngeal branch= (R. pharyngeus) is given off in relation to the superior cervical ganglion, turns around the internal carotid artery, and runs downward and forward on the guttural pouch to the dorsal wall of the pharynx (Fig. 437). Here its branches concur with the pharyngeal branch of the ninth nerve and with filaments from the spinal accessory and the sympathetic in forming the =pharyngeal plexus=. This supplies numerous twigs to the pharynx, and a larger branch which passes along the side of the œsophagus and ramifies in its cervical part.

According to Ellenberger and Baum the pharyngeal plexus receives
filaments also from the digastric, superior laryngeal, hypoglossal,
and first cervical nerves. The branches of the plexus form secondary
intermuscular and submucous plexuses, in which there are numerous
minute ganglia.

2. The =superior= or =anterior laryngeal nerve= (N. laryngeus cranialis) is larger than the preceding and arises a little behind it (Fig. 437). It crosses the deep face of the origin of the external carotid artery, runs downward and forward over the lateral wall of the pharynx behind the hypoglossal nerve, and passes through the foramen below the anterior cornu of the thyroid cartilage. Its terminal branches ramify in the mucous membrane of the larynx, the floor of the pharynx, and the entrance to the œsophagus; they anastomose with those of the recurrent. At its origin the nerve gives off its small =external branch= (R. externus); this descends to the crico-thyroid muscle, which it supplies, and sends filaments to the crico-pharyngeus also. It may arise from the trunk of the vagus or from the pharyngeal branch.

At the point of origin of the superior laryngeal nerve there is a
plexiform widening which is regarded by some authors as the homologue
of the ganglion nodosum of man. From it a filament arises which, after
a short course, rejoins the vagus or enters the sympathetic trunk.
Stimulation of its central end causes a reduction of the
blood-pressure, and it is therefore termed the depressor nerve (N.
depressor).

3. The =recurrent nerve= (N. recurrens), also termed the inferior or posterior laryngeal nerve, differs on the two sides in its point of origin and in the first part of its course. The =right nerve= (Fig. 429) is given off opposite the second rib, turns around the dorso-cervical artery from without inward, runs forward on the lower part of the lateral surface of the trachea, and ascends in the neck on the ventral face of the common carotid artery. The =left nerve= (Fig. 428) arises from the vagus where the latter begins to cross the aortic arch. It passes back over the ligamentum arteriosum, winds around the concavity of the aortic arch from without inward, runs forward on the lower part of the left face of the trachea, and continues in the neck in a similar position to the right nerve.

It is worthy of note that the left nerve passes beneath the bronchial
lymph glands as it winds around the aorta; also that in the next part
of its course it lies between the left surface of the trachea and the
deep face of the aorta, and is then related to lymph glands which lie
along the ventral aspect of the trachea. The left recurrent is often
incorporated in part of its course in the anterior mediastinum with a
deep cardiac nerve. Further, the left nerve lies at first ventral to,
and then upon, the œsophagus in the neck. The right recurrent is given
off from or in common with a considerable trunk which connects the
vagus with the first thoracic ganglion of the sympathetic. The
arrangement here is commonly more or less plexiform, and from it one
or two cardiac nerves arise.

The terminal part of each nerve (Fig. 517) lies on the dorsal surface of the trachea, in relation to the œsophagus internally and the carotid artery above.[206] It passes between the crico-arytenoideus posterior and the crico-pharyngeus; the =terminal branches= supply all the muscles of the larynx except the crico-thyroid, and communicate with branches of the superior laryngeal nerve. =Collateral branches= are given off to the cardiac plexus (Rr. cardiaci), to the trachea (Rr. tracheales), to the œsophagus (Rr. œsophagei), and to the inferior cervical ganglion of the sympathetic.

4. =Cardiac branches= (Rr. cardiaci), usually two or three in number, are given off from each vagus within the thorax (Figs. 428, 429). These concur with the cardiac branches of the sympathetic and recurrent nerves to form the cardiac plexus, which innervates the heart and great vessels.

5. Small =tracheal= and =œsophageal branches= (Rr. tracheales et œsophagei) are given off from both vagi in the thorax. These concur with branches from the recurrent nerves and the inferior cervical and anterior thoracic ganglia of the sympathetic in forming the =posterior tracheal= and =œsophageal plexuses=, from which twigs go to the trachea, œsophagus, heart, and large vessels.