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FIG. 660.- THE DISTRIBUTION OF THE VAGUS NERVE. Va, Right and left vagi ; r, Ganglion jugulare and connexions with Sy, Sympathetic, superior cervical ganglion ;

G.Ph, Glossopharyngeal ; Acc, Accessory nerve ; F, Meningeal branch ; Aur, Auricular branch ; Va, Connexion with ganglion nodosum of vagus ; Sy, Nerve to stylo-hyoid ; Hy, Nerve to hyoglossus; Ci, C2, Loop between the first two cervical nerves ; Sy, Sympathetic, superior cervical ganglion ; Acc, Accessory nerve ; Ph. Pharyngeal branch ; Ph.Pl, Pharyngeal plexus ; S.L, Superior laryngeal nerve ; I.L, Internal laryngeal branch ; E.L, External laryngeal branch ; I.C, Internal, and E.C, External carotid arteries ; Cal, Superior cervical cardiac branch ; Ca2, Inferior cervical cardiac branch ; R.L, Recurrent nerve ; Ca3, Cardiac branches from recurrent nerves ; Ca4, Thoracic cardiac branch (right vagus); A.P.P, Anterior, and P.P.P, Posterior pulmonary plexuses ; Oes. Pl, Esophageal plexus : Cort. Pl, Coeliac plexus.

the large posterior pulmonary plexus, from the lower end of which two nerves emerge on each side. These nerves on the right side pass obliquely over the vena azygos; on the left side they cross the descending thoracic aorta. Both series reach the cesophagus, and divide into small anastomosing branches which form the oesophageal plexus. At the oesophageal opening of the diaphragm the two nerves become separated from the plexus, and entering the abdomen-the left nerve in front of the oesophagus, the right nerve behind it—they terminate by supplying the stomach and other abdominal organs.

The communications and branches of the vagus nerve may be described as (i.) ganglionic, (ii.) cervical, (iii.) thoracic, and (iv.) abdominal (Fig. 660).

Ganglion Jugulare.-The jugular ganglion (O.T. ganglion of the root) is small and spherical. It occupies the jugular foramen, and gives off two branchesmeningeal and auricular.

Ramus Meningeus. — The meningeal branch passes backwards to supply the dura mater of the posterior fossa of the skull.

Ramus Auricularis. — The auricular branch ascends to the ear in a fissure between the jugular and stylo-mastoid foramina. It receives near its origin a twig from the tympanic branch of the glossopharyngeal nerve, and usually communicates with the facial nerve by a branch arising from the latter in the canalis facialis.

The nerve is distributed to the back of the auricle and the external acoustic meatus, and communicates superficially with the posterior auricular nerve.

Communications. Besides supplying the meningeal and auricular branches, this ganglion receives communications from (1) the superior cervical ganglion of the sympathetic; (2) the accessory nerve; and (3) (sometimes) the petrous ganglion of the glossopharyngeal nerve (ramus anastomoticus cum nervo glossopharyngeo).

Ganglion Nodosum. - The ganglion nodosum (O.T. ganglion of the trunk, placed immediately below the preceding, is large and fusiform. Like the jugular ganglion, it supplies two branches—the pharyngeal and superior laryngeal nerves.

Rami Pharyngei. — The pharyngeal branch receives its fibres (through the ganglion) from the accessory nerve. It passes obliquely downwards and medially to the pharynx between the internal and external carotid arteries, and combines with the pharyngeal branches from the glossopharyngeal and superior cervical ganglion of the sympathetic to form the pharyngeal plexus. From this plexus the muscles of the pharynx and soft palate (except the stylopharyngeus and tensor veli palatini) are supplied. The lingual branch is a small nerve which separates itself from the plexus and joins the hypoglossal nerve in the anterior triangle of the neck.

N. Laryngeus Superior.—The superior laryngeal nerve passes obliquely downwards and medially, medial to the external and internal carotid arteries, towards the thyreoid cartilage. It divides in its course into two unequal parts—a larger internal and a smaller external laryngeal branch.

Ramus Internus. — The internal laryngeal branch passes medially into the larynx between the middle and inferior constrictor muscles of the pharynx and through the thyreo-hyoid membrane. It supplies the mucous membrane of the larynx, reaching upwards to the epiglottis and base of the tongue, and forms communications beneath the lamina of the thyreoid cartilage with the branches of the inferior laryngeal nerve (ramus anastomoticus cum nervo laryngeo inferiore).

Ramus Externus.—The external laryngeal branch passes downwards upon the inferior constrictor muscle of the pharynx. It supplies branches to that muscle, and ends in the crico-thyreoid muscle.

Communications. -- Besides supplying these pharyngeal and laryngeal nerves, this ganglion has the following communications with other nerves : (1) with the superior cervical ganglion of the sympathetic; (2) with the hypoglossal; (3) with the loop be veen the first and second cervical nerves; and (4) with he accessory nerve. This nerve applies itself to the ganglion, and thereby supplies to the vagus nerve the inhibitory fibres for the heart, as well as the motor fibres for the pharynx, esophagus, stomach and intestines, larynx and respiratory organs.

Branches of the Vagus in the Neck. In the neck the vagus nerve

supplies cardiac branches and (on the right side) the recurrent (laryngeal) nerve (Fig. 661).

Rami Cardiaci Superiores. The cardiac branches are superior and inferior. On the right side both cardiac branches pass downwards into the thorax behind the subclavian artery, and proceed alongside the trachea to join the deep cardiac plexus. On the left side the two nerves separate on reaching the thorax. The superior nerve passes deeply alongside the trachea to join the deep cardiac plexus. The inferior nerve accompanies the vagus nerve over the aortic arch, along with the superior cervical cardiac branch of the sympathetic, to end in the superficial cardiac plexus.

N. Recurrens. — The right recurrent (laryngeal) nerve arises at the root of the neck, as the vagus crosses in front of the first part of the subclavian artery. It hooks round the artery, and passes obliquely upwards and medially behind the subclavian, the common carotid, and the inferior thyreoid arteries and the thyreoid gland. It finally disappears beneath the inferior border of the inferior constrictor muscle, and, receiving the name of inferior laryngeal nerve, it ends in supplying the muscles of the larynx. In its course it gives off the following branches

(1) Cardiac branches (rami cardiaci inferiores) arise as the nerve winds round the subclavian artery, and course downwards alongside the trachea to end in the deep cardiac plexus.

(2) Communicating branches to the inferior cervical ganglion of the sympathetic arise from the nerve behind the subclavian artery.

(3) Muscular branches supply the trachea, @sophagus (rami tracheales et @sophagei), and the inferior constrictor of the pharynx.

(4) Terminal branches supply the muscles of the larynx (except the crico-thyreoid) and communicate beneath the lamina of the thyreoid cartilage with branches of the internal laryngeal nerve.

Branches of the Vagus in the Thorax.-In the thorax the vagi form the great pulmonary and cesophageal plexuses. The right nerve, in addition, furnishes cardiac branches; and the left nerve gives off the recurrent (laryngeal) nerve.

N. Recurrens.— The left recurrent (laryngeal) nerve differs from the nerve of the right side mainly in its point of origin and in the early part of its course. It springs from the vagus as it crosses the aortic arch, and, after hooking round the arch, lateral to the ligamentum arteriosum, it passes upwards in the superior mediastinum, in the interval between the trachea and esophagus, to the neck. In the neck its course and relations are similar to those of the nerve of the right side. The branches of the nerve are the same as those of the right nerve. The cardiac branches are larger, and, arising below the aortic arch, proceed to the deep cardiac plexus.

Cardiac branches from the right vagus nerve arise in the superior mediastinum, and pass downwards alongside the trachea to join the deep cardiac plexus. On the right side thoracic cardiac branches are thus supplied from both the trunk of the nerve and its recurrent branch; on the left side the cardiac branches in the thorax arise solely from the recurrent branch.

Abdominal Branches. After the formation of the wesophageal plexus the two vagi nerves resume their course, and passing along with the gullet through the diaphragm, terminate by supplying the stomach. The right nerve enters the abdominal cavity behind the gullet, and is distributed to the posterior surface of the stomach. It sends communicating offsets to the celiac, splenic, and renal plexuses. The left nerve applies itself to the anterior surface and small curvature of the stomach, to which it is distributed. It sends communicating offsets along the small curvature of the stomach to the right vagus, and between the layers of the gastro-hepatic ligament to the hepatic plexus.

PLEXUS THORACALES.

Plexus Cardiaci.—The cardiac branches of the vagus nerve (both cervical and thoracic) combine with the cardiac branches of the sympathetic to form the superficial and deep cardiac plexuses.

The superficial cardiac plexus is placed in the hollow of the aortic arch, superficial to the pericardium. It contains a small ganglion (cardiac ganglion of Wrisberg), and is joined by two small nerves—(1) the cardiac branch from the superior cervical ganglion of the sympathetic, and (2) the inferior cervical cardiac branch of the vagus—both of the left side—which reach it after passing over the arch of the aorta.

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Branches and Communications.— From the plexus branches of communication pass (1) to the left half of the deep cardiac plexus, between the aortic arch and the bifurcation of the pulmonary artery; (2) to the left anterior pulmonary plexus along the left branch of the pulmonary artery ; (3) the branches of distribution to the heart extend along the pulmonary artery to join the anterior (right) coronary plexus, which supplies the substance of the heart in the course of the right coronary artery.

Plexus Cardiacus Profundus.—The deep cardiac plexus is much larger. It

is placed behind the arch of the aorta, on the sides of the trachea, just above its bifurcation. It consists of two lateral parts, joined together by numerous communications around the termination of the trachea. The two portions of the plexus are different in their constitution and distribution. The right half of the plexus is joined by both the cervical and thoracic branches of the right vagus and by the branches of the right recurrent nerve, as well as by branches from the superior, middle, and inferior cervical ganglia of the sympathetic. The left half of the plexus is joined by the superior cervical cardiac branch of the left vagus, by branches from the left recurrent nerve, and by branches from the middle and inferior cervical ganglia of the left sympathetic; it also receives a contribution from the superficial cardiac plexus.

The deep cardiac plexus is distributed to the heart and lungs. The right half of the plexus for the most part constitutes the anterior coronary plexus, reaching the heart alongside the ascending aorta, and is distributed to the heart substance in the course of the right coronary artery. It is reinforced by fibres from the superficial cardiac plexus, which reach the heart along the pulmonary artery. Fibres from the right half of the deep cardiac plexus pass also to join the posterior coronary plexus, and others extend laterally to join the anterior pulmonary plexus of the right side.

The left half of the deep cardiac plexus, reinforced by fibres from the superficial cardiac plexuş, is distributed to the heart in the form of the posterior coronary plexus, which is joined by a few fibres behind the pulmonary artery from the right half of the plexus, and supplies the heart substance in the course of the left coronary artery. The left half of the plexus contributes also to the left anterior pulmonary plexus by fibres which extend laterally to the root of the lung along the left branch of the pulmonary artery.

Plexus Pulmonales (Pulmonary Plexuses).—As already stated, the vagus nerve on each side, on reaching the back of the root of the lung, breaks up into numerous plexiform branches for the formation of the posterior pulmonary plexus. From each nerve a few fibres pass to the front of the root of the lung, above its upper border, to form the much smaller anterior pulmonary plexus.

Plexus Pulmonalis Anterior.-The anterior pulmonary plexus on each side is joined by a few fibres from the corresponding part of the deep cardiac plexus, and on the left side from the superficial cardiac plexus as well. It surrounds and supplies the constituents of the root of the lung anteriorly.

Plexus Pulmonalis Posterior. — The posterior pulmonary plexus, placed behind the root of the lung, is formed by the greater part of the vagus nerve, reinforced by fine branches from the second, third, and fourth thoracic ganglia of the sympathetic. Numerous branches proceed from it in a plexiform manner along the bronchi and vessels into the substance of the lung.

Plexus Esophageus Anterior et Posterior (Esophageal Plexus). — The cesophagus in the thorax is supplied by the vagus nerve both in the superior and posterior mediastina. In the superior mediastinum it receives branches from the vagus nerve on the right side, and from its recurrent branch on the left side.

In the posterior mediastinum the gullet is surrounded by the æsophageal plexus, formed from the trunks of the vagi nerves emerging from the posterior pulmonary plexuses, which form a large plexus surrounding the gullet. This part of the csophagus also receives fibres from the greater splanchnic nerve and ganglion. From the resophageal plexus branches supply the muscular wall and mucous membrane of the cesophagus.

Pericardiac branches are also supplied from the plexus to the posterior surface of the pericardium.

NERVUS ACCESSORIUS.

The eleventh or accessory nerve (O.T. spinal accessory) consists of two essentially separate parts, different both in origin and in distribution. One portion is accessory to the vagus nerve, and arises, in series with the fila of that nerve, from the side of the medulla oblongata. The other, spinal portion, arises from

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