_a_, Facial nerve; _b_, posterior auricular nerve; _c_, internal
auricular nerve; _d_, digastric nerve; _e_, inferior buccal nerve;
_f_, cervical branch of facial; _g_, auriculo-palpebral; _h_,
superior buccal nerve; _i_, temporal branch; _k_, _k′_, _k″_,
zygomatic branch; _l_, auriculo-temporal; _m_, malar branch of _l_;
_n_, buccinator nerve; _o_, mylo-hyoid branch; _p_, subcutaneus
malæ; _q_, lacrimal nerve; _r_, frontal nerve; _s_, infratrochlear
nerve; _t_, infraorbital nerve; _1_, paramastoid process; _2_,
digastricus muscle; _3_, base of concha; _4_, masseter; _5_,
zygomaticus; _6_, scutularis; _7_, zygomatic arch; _8_, maxilla.
(Ellenberger-Baum, Anat. d. Hundes.)
]
The =maxillary nerve=, after giving off the zygomatic, divides into
infraorbital and sphenopalatine branches. The =zygomatic nerve= emerges
through an opening in the upper part of the orbital ligament and
ramifies in the lower lid and on the adjacent surface of the face. The
=infraorbital nerves=, two in number, divide within the infraorbital
canal and after their emergence upon the face, thus forming seven or
eight =external nasal= and =superior labial branches=. The
=sphenopalatine nerve= gives off =lesser= and =greater palatine= and
=posterior nasal nerves=.
The =mandibular nerve= passes out through the foramen ovale. The
=superficial temporal nerve= divides into auricular, temporal, and malar
branches; the last-named crosses the masseter and ramifies with the
buccal nerves. The =mylo-hyoid nerve= is given off from the mandibular
nerve almost immediately after the latter emerges from the cranium; it
innervates the mylo-hyoideus and digastricus and gives off a branch
which turns around the lower jaw, joins the inferior buccal nerve, and
ramifies on the lateral surface of the face. The =inferior alveolar
nerve= arises by a common trunk with the mylo-hyoid; it gives off dental
branches and terminates in mental and inferior labial branches. The
=lingual nerve= supplies vasodilator and excito-secretory filaments to
the submaxillary and sublingual salivary glands; these fibers are
derived from the chorda tympani.
The =facial nerve= divides near the posterior border of the jaw into
four branches. The upper branch is the =auriculo-palpebral nerve=, which
divides after a very short course into anterior auricular and zygomatic
branches. The latter curves upward and forward across the zygomatic arch
toward the eye, and divides into branches which supply the eyelids and
nasal region and concur with the frontal and lacrimal nerves in forming
the anterior auricular plexus. The =superior buccal nerve= accompanies
the parotid duct across the masseter. The =inferior buccal nerve= runs
forward along the lower border of the masseter and the mandible. The two
nerves ramify on the cheek and anastomose with each other and the
infraorbital nerves to form a plexus from which branches go to the
muscles of the lips and nostrils. The =cervical branch= runs downward
and backward over the submaxillary gland and ramifies in the cervical
panniculus; it communicates with the inferior buccal nerve and sends
twigs to the parotido-auricularis muscle and the submaxillary space.
The =vagus= bears a =jugular ganglion= and a =ganglion nodosum=. The
latter is situated near the superior cervical ganglion on the rectus
capitis anterior major and dorsal to the carotid artery; it is
fusiform and may be about half an inch (ca. 1 to 1.5 cm.) long in a
large dog. In its course in the neck the nerve is inclosed with the
sympathetic trunk in a common sheath and is related ventrally to the
common carotid artery. The formation of dorsal and ventral =œsophageal
trunks= by the union of the dorsal and ventral divisions of the two
nerves takes place at the hiatus œsophageus. The =dorsal trunk=
concurs with branches of the solar plexus in forming the =posterior
gastric plexus= on the visceral surface of the stomach. The =ventral
trunk= ramifies on the parietal surface of the stomach, forming the
=anterior gastric plexus=, from which a considerable branch passes
along the lesser curvature to the pylorus. Some special features of
the collateral branches are: Two pharyngeal branches are present. The
=superior pharyngeal branch= arises from the vagus above the ganglion
nodosum. It passes under the deep face of the carotid artery and
descends on the lateral surface of the pharynx to end in the
crico-thyroid muscle. It furnishes a root of the inferior pharyngeal
branch, and communicates with the pharyngeal branch of the ninth and
with the superior laryngeal and hypoglossal nerves. The =inferior
pharyngeal branch= is formed by the union of roots derived from the
superior pharyngeal nerve and the ganglion nodosum, together with
filaments from the superior cervical ganglion. It crosses the side of
the pharynx behind the superior pharyngeal and ramifies on the
posterior constrictor of the pharynx and the origin of the œsophagus.
It contributes filaments to the pharyngeal plexus, communicates with
the recurrent nerve, and supplies twigs to the thyroid gland. The
=pharyngeal plexus= is formed on the lateral surface of the pharynx by
branches of the pharyngeal nerves and the communications above
described; branches from it innervate the muscles and mucous membrane
of the pharynx. The =superior laryngeal nerve= arises from the
ganglion nodosum and descends over the side of the pharynx, crossing
beneath the carotid artery and the superior laryngeal nerve. It passes
through the thyroid notch and ramifies in the mucous membrane of the
larynx. It communicates with the superior cervical ganglion and the
superior pharyngeal branch of the vagus, and gives twigs to the
hyo-pharyngeus muscle. Immediately after its entrance into the larynx
it gives off a large branch which, instead of uniting with the
recurrent as in the other animals, has a peculiar arrangement. It runs
back near the dorsal border of the thyroid cartilage, gives a branch
to the crico-arytenoideus posterior as it passes over that muscle, and
continues along the trachea internal to the recurrent nerve. At the
thoracic inlet it communicates with the inferior cervical ganglion and
continues backward to unite with the vagus at or near the point of
origin of the recurrent nerve. Its collateral filaments supply the
trachea and concur with the inferior pharyngeal branch in forming a
plexus on the cervical part of the œsophagus which innervates that
tube.[216] The =depressor nerve= is a very delicate filament which
arises usually from the superior laryngeal nerve and accompanies the
vago-sympathetic trunk to the thorax; its fibers reach the heart
through the cardiac nerves. The =pulmonary= and =posterior œsophageal
plexuses= are highly developed.
The =hypoglossal nerve= gives off a long branch (R. descendens) which
runs downward and backward across the pharynx and larynx, communicates
with the ventral branch of the first cervical nerve, and supplies the
thyro-hyoid, sterno-hyoid, and sterno-thyroid muscles.
The =spinal nerves= number thirty-six or thirty-seven on either side,
and comprise eight cervical, thirteen thoracic, seven lumbar, and five
or six coccygeal.
The =brachial plexus= (Fig. 487) is derived from the ventral branches of
the last four cervical and first thoracic nerves; the root supplied by
the fifth cervical nerve is very small. The roots unite at the lower
border of the scalenus. The more important special features in the
arrangement of the nerves which emanate from the plexus are as follows:
The =musculo-cutaneous nerve= passes between the coraco-brachialis and
the brachial artery and descends in the arm in front of the artery. At
the shoulder joint it gives off branches to the biceps and
coraco-brachialis, and in the lower third of the arm is connected with
the median nerve by an oblique branch. It terminates near the elbow by
dividing into a branch for the brachialis and a small cutaneous nerve
which passes down over the inner face of the elbow and, inclining a
little forward, descends over the deep fascia of the forearm to the
carpus.
The =radial nerve= descends behind the ulnar nerve, gives branches to
the extensors of the elbow, dips in between the internal head of the
triceps and the accessory head of the anconeus, winds around the arm,
and divides between the brachialis and the external head of the triceps
into two branches. The =deep branch= (R. profundus) supplies the
extensor and supinator muscles on the forearm. The =superficial branch=
(R. superficialis) emerges upon the flexor surface of the elbow and
divides into two branches which terminate by supplying two =dorsal
digital nerves= to each digit, except the fifth, which receives its
outer dorsal nerve from the ulnar. The inner branch descends along the
inner side of the cephalic vein to the carpus, where it divides into
dorsal digital nerves for the first digit and the inner side of the
second. The outer branch is much larger. It runs downward on the middle
of the front of the forearm and supplies the remaining dorsal digital
nerves except that to the outer side of the fifth digit.
The =ulnar nerve= is as large as or larger than the median, with which
it is united for some distance. At the distal third of the arm it
separates from the median and passes over the internal epicondyle of the
humerus. At the proximal part of the forearm it gives off the =dorsal
branch= (R. dorsalis), which supplies cutaneous twigs to the
dorso-lateral surface of the lower part of the forearm and carpus and
terminates as the =external dorsal digital nerve= of the fifth digit.
Descending under cover of the flexor carpi ulnaris, the ulnar nerve
inclines inward under the tendon of insertion of that muscle and divides
into superficial and deep branches. The =superficial branch= (R.
superficialis) runs downward along the outer border of the flexor
tendons, gives off the =external volar digital nerve of the fifth digit=
(N. dig. vol. lat. dig. V), and a branch (N. met. vol. IV) which
descends in the space between the fourth and fifth metacarpal bones and
unites with the deep branch. The =deep branch= (R. profundus) descends
in the carpal canal and divides under the deep flexor tendon into its
terminal branches. The smaller of these supply the volar metacarpal
muscles. The larger terminals are the three =volar common digital
nerves= (Nn. dig. vol. comm. II, III, IV), which descend along the
second, third, and fourth intermetacarpal spaces, subdivide, and concur
with the volar metacarpal branches of the median nerve in forming the
=volar proper digital nerves= (Nn. dig. vol. proprii).
The =median nerve= descends behind the brachial artery, passes over the
internal epicondyle of the humerus, then under the pronator teres, and
continues in the forearm under cover of the flexor carpi radialis. It
gives branches below the elbow to the flexor and pronator muscles, and
lower down a palmar branch to the skin on the inner and posterior aspect
of the carpus, and terminates between the superficial and deep flexor
tendons by dividing into three =volar metacarpal nerves= (N. met. vol.
I, II, III). These descend in the first, second, and third
intermetacarpal spaces and unite with the volar common digital nerves in
forming volar proper digital nerves. The arrangement of the digital
nerves is indicated in the annexed schematic figures.
[Illustration:
FIG. 547.—NERVES OF DISTAL PART OF RIGHT FORE LIMB OF DOG, ANTERIOR
VIEW (SCHEMATIC).
_p_, Dorsal proper digital nerves.
]
[Illustration:
FIG. 548.—NERVES OF DISTAL PART OF RIGHT FORE LIMB OF DOG, POSTERIOR
VIEW (SCHEMATIC).
_p_, Volar proper digital nerves.
]
The =lumbo-sacral plexus= is formed from the ventral branches of the
last five lumbar and first sacral nerves. The more important special
facts in regard to the nerves of the pelvic limb are as follows:
The =saphenous nerve= (Fig. 492) is relatively large, and, in fact,
might be considered as the continuation of the femoral nerve. It
descends at first in front of the femoral artery, then passes over the
lower part of the inner surface of the thigh with the saphenous artery,
continues down the leg with the dorsal branch of that vessel, and
anastomoses with branches of the superficial peroneal nerve. It supplies
cutaneous twigs from the stifle to the metatarsus.
The =peroneal nerve= separates from the tibial above the origin of the
gastrocnemius, runs downward and forward across the outer head of that
muscle, passes between the deep flexor of the digit and the peroneus
longus, and divides into superficial and deep branches. The =superficial
peroneal nerve= descends the leg along the peroneus tertius and longus,
gives off a =dorsal branch= to the first digit (N. cutaneus dorsalis
medialis), and divides at the proximal part of the metatarsus into three
=dorsal common digital nerves= (Nn. dig. pedis dors. comm. II, III, IV).
These descend with the superficial dorsal metatarsal arteries and concur
with branches of the deep peroneal nerve in forming =dorsal proper
digital nerves= (Nn. dig. ped. prop. dorsales). The =deep peroneal
nerve= passes down the leg with the anterior tibial vessels. It gives
twigs to the hock joint and the extensor brevis muscle, and divides into
three =dorsal metatarsal nerves= (Nn. met. dors. II, III, IV); these
descend with the corresponding arteries along the intermetatarsal spaces
and unite with the dorsal common digital nerves in supplying the dorsal
proper digital nerves.
[Illustration:
FIG. 549.—NERVES OF DISTAL PART OF RIGHT HIND LIMB OF DOG, ANTERIOR
VIEW (SCHEMATIC).
_p_, Dorsal proper digital nerves.
]
[Illustration:
FIG. 550.—NERVES OF DISTAL PART OF RIGHT HIND LIMB OF DOG, POSTERIOR
VIEW (SCHEMATIC).
_p_, Plantar proper digital nerves.
]
The =tibial nerve= divides at the tarsus into two plantar branches. The
=internal plantar nerve= descends along the inner border of the
superficial flexor tendon and divides near the middle of the metatarsus
into two branches. Of these, the internal branch constitutes the =first
plantar common digital nerve= (N. dig. comm. plant. I). The outer branch
descends on the superficial flexor tendon and divides into three
=plantar metatarsal nerves= (Nn. met. plant. II, III, IV), which unite
with the plantar common digital nerves. The =external plantar nerve=
passes down between the flexor tendons, sends twigs to the muscles on
the plantar surface of the metatarsus, and divides into three =plantar
common digital nerves= (Nn. dig. comm, plant. II, III, IV). These
descend with the deep plantar metatarsal arteries in the second, third,
and fourth intermetatarsal spaces, receive the plantar metatarsal
nerves, and divide into =plantar proper digital nerves=, which pass down
the opposed surfaces of the second to the fifth digits.
The =sympathetic system= presents few special features worthy of
mention. The =superior cervical ganglion= lies above the ganglion
nodosum close to the cranial base and internal to the origin of the
internal carotid and occipital arteries. It forms connections directly
or through the carotid plexus with the last seven cranial and first
cervical nerves. The =cervical trunk= unites with the vagus so
intimately as to form a vago-sympathetic trunk. There may be a small
=middle cervical ganglion= in front of the inferior cervical ganglion.
The latter is usually distinct from the first thoracic ganglion, which
is stellate and lies on the longus colli opposite the second rib and
intercostal space.