1.
10th, 11th,
12th
cranial nerves
2.
Cervical plexus. Organ of taste
3.
Preparation of brain and cranial nerves
Lesson No 23
Theme
1. 10th, 11th,
12th
cranial nerves
X Vagus nerve (mixed) contains motor
fibers which start from nucleus ambiguus, parasympathetic (preganglionic) fibers
form dorsal nucleus and sensory
fibers from superior and inferior ganglia in jugular foramen.
·Cranial part of vagus nerve gives off the following branches:
Meningeal branch which starts from superior ganglion and passes
to cranial dura mater in posterior cranial fossa;
Auricular
branch, which starts from superior ganglion
,
passes over mastoid canalicule of temporal bone and
innervates the skin of external surface of auricle and posterior wall of
external acoustic meatus.
The vagus nerve is composed of
both motor and sensory fibers, and has a more
extensive course and distribution than any of the other cranial nerves, since
it passes through the neck and thorax to the abdomen.
Upper part of medulla spinalis
and hind- and mid-brains; posterior aspect, exposed in situ
The vagus is attached by eight or
ten filaments to the medulla oblongata in the groove between the olive and the
inferior peduncle, below the glossopharyngeal. The sensory fibers arise from the cells of the jugular
ganglion and ganglion nodosum of the nerve, and, when
traced into the medulla oblongata mostly end by arborizing around the cells of
the inferior part of a nucleus which lies beneath the ala
cinerea in the lower part of the rhomboid fossa.
These are the sympathetic afferent fibers. Some of
the sensory fibers of the glossopharyngeal nerve have
been seen to end in the upper part of this nucleus. A few of the sensory fibers of the vagus, probably taste
fibers, descend in the fasciculus solitarius and end around its cells. The somatic sensory
fibers, few in number, from the posterior part of
the external auditory meatus and the back of the ear, probably join the spinal
tract of the trigeminal as it descends in the medulla. The somatic motor fibers arise from the cells of the nucleus ambiguus, already referred to in connection with the motor
root of the glossopharyngeal nerve.
The sympathetic efferent fibers, distributed
probably as preganglionic fibers to the thoracic and
abdominal viscera, i. e., as motor fibers to the bronchial tree, inhibitory fibers to the heart, motor fibers
to the esophagus, stomach, small intestine and gall
passages, and as secretory fibers to the stomach and
pancreas, arise from the dorsal nucleus of the vagus.
The filaments of the nerve unite, and form a flat cord,
which passes beneath the flocculus to the jugular
foramen, through which it leaves the cranium. In emerging through this opening,
the vagus is accompanied by and contained in the same
sheath of dura mater with the accessory nerve, a
septum separating them from the glossopharyngeal which lies in front .
In this situation the vagus presents a well-marked
ganglionic enlargement, which is called the jugular ganglion (ganglion
of the root); to it the accessory nerve is connected by one or two filaments.
After its exit from the jugular foramen the vagus is
joined by the cranial portion of the accessory nerve, and enlarges into a
second gangliform swelling, called the ganglion nodosum (ganglion of the trunk); through this
the fibers of the cranial portion of the accessory
pass without interruption, being principally distributed to the pharyngeal and
superior laryngeal branches of the vagus, but some of
its fibers descend in the trunk of the vagus, to be distributed with the recurrent nerve and probably
also with the cardiac nerves.
The vagus nerve passes vertically down the
neck within the carotid sheath, lying between the internal jugular vein and
internal carotid artery as far as the upper border of the thyroid cartilage,
and then between the same vein and the common carotid artery to the root of the
neck. The further course of the nerve differs on the two sides of the body.
On the right side, the nerve passes across the subclavian artery between it and the right innominate vein,
and descends by the side of the trachea to the back of the root of the lung,
where it spreads out in the posterior pulmonary plexus. From the lower
part of this plexus two cords descend on the esophagus,
and divide to form, with branches from the opposite nerve, the esophageal plexus. Below, these branches are
collected into a single cord, which runs along the back of the esophagus enters the abdomen, and is distributed to the postero-inferior surface of the stomach, joining the left
side of the celiac plexus, and sending filaments to the lienal
plexus.
Course and
distribution of the glossopharyngeal, vagus, and
accessory nerves
On the left side, the vagus
enters the thorax between the left carotid and subclavian
arteries, behind the left innominate vein. It crosses the left side of the arch
of the aorta, and descends behind the root of the left lung, forming there the posterior
pulmonary plexus. From this it runs along the anterior surface of the esophagus, where it unites with the nerve of the right side
in the esophageal plexus, and is
continued to the stomach, distributing branches over its anterosuperior
surface; some of these extend over the fundus, and others along the lesser
curvature. Filaments from these branches enter the lesser omentum,
and join the hepatic plexus.
The Jugular Ganglion (ganglion jugulare;
ganglion of the root) is of a grayish color, spherical in form, about
Branches of Communication.—This ganglion is connected by
several delicate filaments to the cranial portion of the accessory nerve; it
also communicates by a twig with the petrous ganglion of the glossopharyngeal,
with the facial nerve by means of its auricular branch, and with the
sympathetic by means of an ascending filament from the superior cervical
ganglion.
The Ganglion Nodosum (ganglion
of the trunk; inferior ganglion) is cylindrical in form, of a reddish color, and
Branches of Communication.—This ganglion
is connected with the hypoglossal, the superior cervical ganglion of the
sympathetic, and the loop between the first and second cervical nerves.
Branches of Distribution.—The branches of
distribution of the vagus are:
In the Jugular Fossa…
Meningeal.
Auricular.
In the Neck…………
Pharyngeal.
Superior laryngeal.
Recurrent.
Superior cardiac.
In the Thorax……….
Inferior cardiac.
Anterior bronchial.
Posterior bronchial.
Esophageal.
In the Abdomen…….
Gastric.
Celiac.
Hepatic.
The Meningeal Branch (ramus meningeus;
dural branch) is a recurrent filament given off
from the jugular ganglion; it is distributed to the dura
mater in the posterior fossa of the base of the skull.
The Auricular Branch (ramus auricularis;
nerve of
The Pharyngeal Branch (ramus pharyngeus),
the principal motor nerve of the pharynx, arises from the upper part of
the ganglion nodosum, and consists principally of
filaments from the cranial portion of the accessory nerve. It passes across the
internal carotid artery to the upper border of the Constrictor pharyngis medius, where it
divides into numerous filaments, which join with branches from the
glossopharyngeal, sympathetic, and external laryngeal to form the pharyngeal
plexus. From the plexus, branches are distributed to the muscles and mucous
membrane of the pharynx and the muscles of the soft palate, except the Tensor veli palatini. A minute filament
descends and joins the hypoglossal nerve as it winds around the occipital artery.
The Superior Laryngeal Nerve (n. laryngeus superior) larger than the preceding,
arises from the middle of the ganglion nodosum
and in its course receives a branch from the superior cervical ganglion of the
sympathetic. It descends, by the side of the pharynx, behind the internal
carotid artery, and divides into two branches, external and internal.
The external branch (ramus externus),
the smaller, descends on the larynx, beneath the Sternothyreoideus,
to supply the Cricothyreoideus. It gives branches to
the pharyngeal plexus and the Constrictor pharyngis
inferior, and communicates with the superior cardiac nerve, behind the common
carotid artery.
The internal branch (ramus internus)
descends to the hyothyroid membrane, pierces it in company
with the superior laryngeal artery, and is distributed to the mucous membrane
of the larynx. Of these branches some are distributed to the epiglottis, the
base of the tongue, and the epiglottic glands; others
pass backward, in the aryepiglottic fold, to supply
the mucous membrane surrounding the entrance of the larynx, and that lining the
cavity of the larynx as low down as the vocal folds. A filament descends
beneath the mucous membrane on the inner surface of the thyroid cartilage and
joins the recurrent nerve.
The Recurrent Nerve (n. recurrens;
inferior or recurrent laryngeal nerve) arises, on the right side,
in front of the subclavian artery; winds from before
backward around that vessel, and ascends obliquely to the side of the trachea
behind the common carotid artery, and either in front of or behind the inferior
thyroid artery. On the left side, it arises on the left of the
arch of the aorta, and winds below the aorta at the point where the ligamentum arteriosum is
attached, and then ascends to the side of the trachea. The nerve on either side
ascends in the groove between the trachea and esophagus,
passes under the lower border of the Constrictor pharyngis
inferior, and enters the larynx behind the articulation of the inferior cornu of the thyroid cartilage with the cricoid; it is
distributed to all the muscles of the larynx, excepting the Cricothyreoideus.
It communicates with the internal branch of the superior laryngeal nerve, and
gives off a few filaments to the mucous membrane of the lower part of the
larynx.
As the recurrent nerve hooks around the subclavian
artery or aorta, it gives off several cardiac filaments to the deep part of the
cardiac plexus. As it ascends in the neck it gives off branches, more numerous
on the left than on the right side, to the mucous membrane and muscular coat of
the esophagus; branches to the mucous membrane and
muscular fibers of the trachea; and some pharyngeal
filaments to the Constrictor pharyngis inferior.
The Superior Cardiac Branches (rami cardiaci superiores; cervical
cardiac branches), two or three in number, arise from the vagus, at the upper and lower parts of the neck.
The upper branches are small, and communicate with
the cardiac branches of the sympathetic. They can be traced to the deep part of
the cardiac plexus.
The lower branch arises at the root of the
neck, just above the first rib. That from the right vagus
passes in front or by the side of the innominate artery, and proceeds to the
deep part of the cardiac plexus; that from the left runs down across the left
side of the arch of the aorta, and joins the superficial part of the cardiac
plexus.
·Cervical part of vagus
nerve gives off:
Pharyngeal branches
with branches of Glossopharyngeal nerve and sympathetic trunk form pharyngeal plexus, that innervates mucous
membrane and muscles of the throat (superior and middle constrictors; levator veli palatini,
palatopharyngeus and palatoglossus,
uvulae muscles).
Superior cervical cardiac branches
pass downward along common carotid artery and communicate with sympathetic nerves, enter
into cardiac plexus and supply the heart (sensory and parasympathetic
innervating).
Superior laryngeal nerve
originate from inferior ganglion and carry sensory, motor and parasympathetic
preganglionic fibers. Motor fibers of the external
branch innervate cricothyroid and inferior
constrictor muscles, sensory fibers (internal
branch) supply mucous membrane of the larynx over vocal fold, mucous
membrane of the epiglottis and tongue root.
Recurrent laryngeal nerve
passes upward between esophagus and trachea and sends a numerous twigs. Inferior laryngeal nerve supplies mucous
membrane of the larynx below vocal fold and the rest of muscles (thyroarytenoid, lateral and posterior cricoarytenoid,
transverse and oblique arytenoid, vocalis). Tracheal, esophageal and inferior cervical cardiac branches
supply internal organs.
Thoracic part of vagus
nerve gives off:
Thoracic cardiac branches
which pass to cardiac plexus;
Bronchial branches
with sympathetic nerves form pulmonary plexus. Last enters in lungs with
bronchi.
Esophageal
branches form esophageal plexus round
this organ.
·
Hypoglossal nerve,
cervical plexus, and their branches
The
accessory nerve consists of two parts: a cranial and a spinal.
The
Cranial Part (ramus internus; accessory
portion) is the smaller of the two. Its fibers arise from the cells
of the nucleus ambiguus and emerge as four or
five delicate rootlets from the side of the medulla oblongata, below the roots
of the vagus. It runs lateralward
to the jugular foramen, where it interchanges fibers with the spinal portion or
becomes united to it for a short distance; here it is also connected by one or
two filaments with the jugular ganglion of the vagus.
It then passes through the jugular foramen, separates from the spinal portion
and is continued over the surface of the ganglion nodosum
of the vagus, to the surface of which it is adherent,
and is distributed principally to the pharyngeal and superior laryngeal
branches of the vagus. Through the pharyngeal branch
it probably supplies the Musculus uvulæ
and Levator veli palatini. Some few filaments from it are continued into the
trunk of the vagus below the ganglion, to be
distributed with the recurrent nerve and probably also with the cardiac nerves.
The
Spinal Part (ramus externus; spinal portion)
is firm in texture, and its fibers arise from the motor cells in the
lateral part of the anterior column of the gray substance of the medulla spinalis as low as the fifth cervical nerve. Passing
through the lateral funiculus of the medulla spinalis, they emerge on its surface and unite to form a
single trunk, which ascends between the ligamentum denticulatum and the posterior roots of the spinal nerves;
enters the skull through the foramen magnum, and is then directed to the
jugular foramen, through which it passes, lying in the same sheath of dura mater as the vagus, but
separated from it by a fold of the arachnoid. In the jugular foramen, it
receives one or two filaments from the cranial part of the nerve, or else joins
it for a short distance and then separates from it again. As its exit from the
jugular foramen, it runs backward in front of the internal jugular vein in 66.6
per cent. of cases, and behind in it 33.3 per cent. (Tandler). The nerve then descends
obliquely behind the Digastricus and Stylohyoideus to the upper part of the Sternocleidomastoideus;
it pierces this muscle, and courses obliquely across the posterior triangle of
the neck, to end in the deep surface of the Trapezius. As it traverses the Sternocleidomastoideus it gives several filaments to the
muscle, and joins with branches from the second cervical nerve. In the
posterior triangle it unites with the second and third cervical nerves, while
beneath the Trapezius it forms a plexus with the third and fourth cervical
nerves, and from this plexus fibers are distributed to the muscle.
The Hypoglossal Nerve
(N. Hypoglossus; Twelfth Nerve)
The hypoglossal nerve is the motor nerve of the
tongue.
Its fibers arise from the cells of the hypoglossal
nucleus, which is an upward prolongation of the base of the anterior column
of gray substance of the medulla spinalis. This
nucleus is about
The rootlets of this nerve are collected into two bundles, which
perforate the dura mater separately, opposite the
hypoglossal canal in the occipital bone, and unite together after their passage
through it; in some cases the canal is divided into two by a small bony
spicule. The nerve descends almost vertically to a point corresponding with the
angle of the mandible. It is at first deeply seated beneath the internal
carotid artery and internal jugular vein, and intimately connected with the vagus nerve; it then passes forward between the vein and
artery, and lower down in the neck becomes superficial below the Digastricus. The nerve then loops around the occipital
artery, and crosses the external carotid and lingual arteries below the tendon
of the Digastricus. It passes beneath the tendon of
the Digastricus, the Stylohyoideus,
and the Mylohyoideus, lying between the last-named
muscle and the Hyoglossus, and communicates at the
anterior border of the Hyoglossus with the lingual
nerve; it is then continued forward in the fibers of the Genioglossus
as far as the tip of the tongue, distributing branches to its muscular
substance.
Branches of
Communication.—Its branches of communication are, with the
Vagus. First
and second cervical nerves.
Sympathetic. Lingual.
The communications with the vagus take place
close to the skull, numerous filaments passing between the hypoglossal and the
ganglion nodosum of the vagus
through the mass of connective tissue which unites the two nerves. As the nerve
winds around the occipital artery it gives off a filament to the pharyngeal plexus.
The communication with the sympathetic takes place opposite
the atlas by branches derived from the superior cervical ganglion, and in the
same situation the nerve is joined by a filament derived from the loop
connecting the first and second cervical nerves.
The communications with the lingual take place near the
anterior border of the Hyoglossus by numerous
filaments which ascend upon the muscle.
Branches of Distribution.—The branches of distribution of the hypoglossal nerve are:
Meningeal. Thyrohyoid.
Descending. Muscular.
Of these branches, the meningeal, descending, thyrohyoid, and the muscular twig to the Geniohyoideus, are probably derived mainly from the branch
which passes from the loop between the first and second cervical to join the
hypoglossal
Meningeal Branches (dural branches).—As the hypoglossal nerve passes through the hypoglossal canal it gives
off, according to Luschka, several filaments to the dura mater in the posterior fossa of the skull.
The Descending Ramus (ramus descendens;
descendens hypoglossi),
long and slender, quits the hypoglossal where it turns around the occipital
artery and descends in front of or in the sheath of the carotid vessels; it
gives a branch to the superior belly of the Omohyoideus,
and then joins the communicantes cervicales
from the second and third cervical nerves; just below the middle of the neck,
to form a loop, the ansa hypoglossi. From the convexity of this loop branches
pass to supply the Sternohyoideus, the Sternothyreoideus, and the inferior belly of the Omohyoideus. According to
The Thyrohyoid Branch
(ramus thyreohyoideus) arises from the hypoglossal
near the posterior border of the hyoglossus; it runs
obliquely across the greater cornu of the hyoid bone,
and supplies the Thyreohyoideus muscle.
The Muscular Branches are distributed to the Styloglossus, Hyoglossus, Geniohyoideus, and Genioglossus.
At the under surface of the tongue numerous slender branches pass upward into
the substance of the organ to supply its intrinsic muscles.
Short motor branches run directly to the deep cervical muscles: the anterior and lateral rectus capitis muscles,
and the longus
capitus and longus colli muscles
of the head and neck, anterior,
middle and posterior scalenus muscles, also sternocleidomastoid and trapezius muscles. Fibers associated with the
hypoglossal nerve and form
the ansa cervicalis that
innervates the infrahyoid muscles: the omohyoid,
sternothyroid and sternohyoid,
thyrohyoid.
The sensory nerves of the plexus penetrate the fascia behind the
sternocleidomastoid muscle:
· transverse cervical nerve of the neck (supplies the anterior cervical region)
· lesser occipital nerve (for lateral occipital region)
· supraclavlcular nerves (supply the supraclavicular region,
the shoulder and the upper thoracic region)
The Phrenic nerve (mixed) enters the superior thoracic
aperture and runs through the mediastinum to the diaphragm, giving off small
branches for the sensory innervation of the pericardium. It divides on the surface of
the diaphragm to supply all the diaphragmatic muscle. Branches provide the sensory
fibers to the serous coverings of the diaphragm, the pleura cranially and caudally the peritoneum covering it and the liver and
gallbladder.
Plan of hypoglossal nerve
Theme 3. preparations OF
BRAIN AND CRANIAL NERVES
The inferior surface is concave, and is continuous posteriorly
with the tentorial surface of the occipital lobe. It
is traversed by the inferior temporal sulcus, which extends from near
the occipital pole behind, to within a short distance of the temporal pole in
front, but is frequently subdivided by bridging gyri.
Lateral to this fissure is the narrow tentorial part
of the inferior temporal gyrus, and medial to it the fusiform gyrus,
which extends from the occipital to the temporal pole; this gyrus
is limited medially by the collateral fissure, which separates it from the
lingual gyrus behind and from the hippocampal gyrus in front.
The Insula (island of Reil;
central lobe) lies deeply in the lateral or Sylvian
fissure, and can only be seen when the lips of that fissure are widely
separated, since it is overlapped and hidden by the gyri
which bound the fissure. These gyri are termed the opercula
of the insula; they are separated from each other by the three rami of the
lateral fissure, and are named the orbital, frontal, frontoparietal,
and temporal
opercula.
The orbital operculum lies below the anterior horizontal ramus of the
fissure, the frontal between this and the anterior ascending ramus, the parietal
between the anterior ascending ramus and the upturned end of the posterior
ramus, and the temporal below the posterior ramus. The frontal operculum
is of small size in those cases where the anterior horizontal and ascending
rami of the lateral fissure arise from a common stem. The insula is surrounded
by a deep circular sulcus which separates it from the frontal, parietal,
and temporal lobes. When the opercula have been removed, the insula is seen as
a triangular eminence, the apex of which is directed toward the anterior
perforated substance. It is divided into a larger anterior and a smaller
posterior part by a deep sulcus, which runs backward and upward from the apex
of the insula. The anterior part is subdivided by shallow sulci into three or
four short gyri, while the posterior part is
formed by one long gyrus, which is often
bifurcated at its upper end. The cortical gray substance of the insula is
continuous with that of the different opercula, while its deep surface
corresponds with the lentiform nucleus of the corpus
striatum.
The term limbic lobe was
introduced by Broca, and under it he included the
cingulate and hippocampal gyri, which together arch
around the corpus callosum and the hippocampal fissure. These he separated on
the morphological ground that they are well-developed in animals possessing a
keen sense of smell (osmatic animals), such as the dog and fox. They were thus
regarded as a part of the rhinencephalon, but it is
now recognized that they belong to the neopallium;
the cingulate gyrus is therefore sometimes described
as a part of the frontal lobe, and the hippocampal as a part of the temporal
lobe
The insula of the left side, exposed by
removing the opercula.
.
The Thalamencephalon.—The thalamencephalon
comprises: (1) the thalamus; (2) the metathalamus
or corpora geniculata; and (3) the epithalamus, consisting of the
trigonum habenulæ, the pineal body, and the
posterior commissure.
Dissection showing the ventricles of the
brain.
Connections.—The thalamus may be
regarded as a large ganglionic mass in which the ascending tracts of the tegmentum and a considerable proportion of the fibers of the optic tract end, and from the cells of which
numerous fibers (thalamocortical)
take origin, and radiate to almost every part of the cerebral cortex. The lemniscus, together with the other longitudinal strands of
the tegmentum, enters its ventral part: the thalamomammillary fasciculus (bundle of Vicq d’Azyr), from the corpus
mammillare, enters in its anterior tubercle, while
many of the fibers of the optic tract terminate in
its posterior end. The thalamus also receives numerous fibers
(corticothalamic) from the cells of the cerebral
cortex. The fibers that arise from the cells of the
thalamus form four principal groups or stalks: (a) those of the anterior
stalk pass through the frontal part of the internal capsule to the frontal
lobe; (b) the fibers of the posterior stalk
(optic radiations) arise in the pulvinar and
are conveyed through the occipital part of the internal capsule to the
occipital lobe; (c) the fibers of the inferior
stalk leave the under and medial surfaces of the thalamus, and pass beneath
the lentiform nucleus to the temporal lobe and
insula; (d) those of the parietal stalk pass from the lateral
nucleus of the thalamus to the parietal lobe. Fibers
also extend from the thalamus into the corpus striatum—those destined for the
caudate nucleus leave the lateral surface, and those for the lentiform nucleus, the inferior surface of the thalamus.
The Metathalamus comprises
the geniculate bodies, which are two in number—a medial and a lateral—on
each side.
X Vagus nerve (mixed) contains motor
fibers which start from nucleus ambiguus, parasympathetic (preganglionic) fibers
form dorsal nucleus and sensory
fibers from superior and inferior ganglia in jugular foramen.
·Cranial part of vagus nerve gives off the following branches:
Meningeal branch which starts from superior ganglion and passes
to cranial dura mater in posterior cranial fossa;
Auricular
branch, which starts from superior ganglion
,
passes over mastoid canalicule of temporal bone and
innervates the skin of external surface of auricle and posterior wall of
external acoustic meatus.
The vagus nerve is composed of
both motor and sensory fibers, and has a more
extensive course and distribution than any of the other cranial nerves, since
it passes through the neck and thorax to the abdomen.
Upper part of medulla spinalis
and hind- and mid-brains; posterior aspect, exposed in situ
The vagus is attached by eight or
ten filaments to the medulla oblongata in the groove between the olive and the
inferior peduncle, below the glossopharyngeal. The sensory fibers arise from the cells of the jugular
ganglion and ganglion nodosum of the nerve, and, when
traced into the medulla oblongata mostly end by arborizing around the cells of
the inferior part of a nucleus which lies beneath the ala
cinerea in the lower part of the rhomboid fossa.
These are the sympathetic afferent fibers. Some of
the sensory fibers of the glossopharyngeal nerve have
been seen to end in the upper part of this nucleus. A few of the sensory fibers of the vagus, probably taste
fibers, descend in the fasciculus solitarius and end around its cells. The somatic sensory
fibers, few in number, from the posterior part of
the external auditory meatus and the back of the ear, probably join the spinal
tract of the trigeminal as it descends in the medulla. The somatic motor fibers arise from the cells of the nucleus ambiguus, already referred to in connection with the motor
root of the glossopharyngeal nerve.
The sympathetic efferent fibers, distributed
probably as preganglionic fibers to the thoracic and
abdominal viscera, i. e., as motor fibers to the bronchial tree, inhibitory fibers to the heart, motor fibers
to the esophagus, stomach, small intestine and gall
passages, and as secretory fibers to the stomach and
pancreas, arise from the dorsal nucleus of the vagus.
The filaments of the nerve unite, and form a flat cord,
which passes beneath the flocculus to the jugular
foramen, through which it leaves the cranium. In emerging through this opening,
the vagus is accompanied by and contained in the same
sheath of dura mater with the accessory nerve, a
septum separating them from the glossopharyngeal which lies in front .
In this situation the vagus presents a well-marked
ganglionic enlargement, which is called the jugular ganglion (ganglion
of the root); to it the accessory nerve is connected by one or two filaments.
After its exit from the jugular foramen the vagus is
joined by the cranial portion of the accessory nerve, and enlarges into a
second gangliform swelling, called the ganglion nodosum (ganglion of the trunk); through this
the fibers of the cranial portion of the accessory
pass without interruption, being principally distributed to the pharyngeal and
superior laryngeal branches of the vagus, but some of
its fibers descend in the trunk of the vagus, to be distributed with the recurrent nerve and probably
also with the cardiac nerves.
The vagus nerve passes vertically down the
neck within the carotid sheath, lying between the internal jugular vein and
internal carotid artery as far as the upper border of the thyroid cartilage,
and then between the same vein and the common carotid artery to the root of the
neck. The further course of the nerve differs on the two sides of the body.
On the right side, the nerve passes across the subclavian artery between it and the right innominate vein,
and descends by the side of the trachea to the back of the root of the lung,
where it spreads out in the posterior pulmonary plexus. From the lower
part of this plexus two cords descend on the esophagus,
and divide to form, with branches from the opposite nerve, the esophageal plexus. Below, these branches are
collected into a single cord, which runs along the back of the esophagus enters the abdomen, and is distributed to the postero-inferior surface of the stomach, joining the left
side of the celiac plexus, and sending filaments to the lienal
plexus.
Course and
distribution of the glossopharyngeal, vagus, and
accessory nerves
On the left side, the vagus
enters the thorax between the left carotid and subclavian
arteries, behind the left innominate vein. It crosses the left side of the arch
of the aorta, and descends behind the root of the left lung, forming there the posterior
pulmonary plexus. From this it runs along the anterior surface of the esophagus, where it unites with the nerve of the right side
in the esophageal plexus, and is
continued to the stomach, distributing branches over its anterosuperior
surface; some of these extend over the fundus, and others along the lesser
curvature. Filaments from these branches enter the lesser omentum,
and join the hepatic plexus.
The Jugular Ganglion (ganglion jugulare;
ganglion of the root) is of a grayish color, spherical in form, about
Branches of Communication.—This ganglion is connected by
several delicate filaments to the cranial portion of the accessory nerve; it
also communicates by a twig with the petrous ganglion of the glossopharyngeal,
with the facial nerve by means of its auricular branch, and with the
sympathetic by means of an ascending filament from the superior cervical
ganglion.
The Ganglion Nodosum (ganglion
of the trunk; inferior ganglion) is cylindrical in form, of a reddish color, and
Branches of Communication.—This ganglion is connected with the hypoglossal, the
superior cervical ganglion of the sympathetic, and the loop between the first
and second cervical nerves.
Hind- and mid-brains; postero-lateral view.