342. NERVOUS SYSTEM. 



THE PAR VAGUM, being disunited from the giosso-pha- 

 ryngeal nerve, proceeds downward and backward to join the caro- 

 tid artery, in the same cellular sheath with which, to the out- 

 ward side of the vessel, it takes its course along the neck to 

 the chest. Its cervical branches are — 1. Two or three twigs 

 to the superior cervical ganglion. 2. The pharyngeal branch, 

 reflected upon the side of the pharynx ; whose filaments are — 

 a. To the esophagus, b. One received from the sympathetic. 

 c. The continuation of the nerve, which is expended in the sub- 

 stance of the pharynx. 3. Two slender branches to the carotid 

 artery, upon the coats of which they ramify, unite, and ulti- 

 mately split into twigs, forming a sort of plexus around the ves- 

 sel at its bifurcation, from which other filaments are sent along 

 the parietes both of the external and internal carotids. 4. The 

 laryngeal branch, crossing above the carotid artery, then wind- 

 ing downward upon the side of the pharynx, in its way to the 

 larynx, and entering a perforation through the posterior ala of the 

 thyroid cartilage. 



Along the posterior part of the neck the par vagum inclines up- 

 ward, and is found above the carotid artery, between which vessel 

 and the axillary artery it continues its course, through the space be- 

 tween the two first ribs, into the chest. Havingentered the thoracic 

 cavity, it runs within the superior mediastinum ; but it has a some- 

 what different relative situation on one side from what it has on the 

 other : the right nerve adheres in its passage to the side of the 

 trachea, crosses above the root of the right lung, alongside of 

 the esophagus, and gains the under surface of that tube before 

 it leaves the chest ; whereas, on the left side, the nerve accom- 

 panies the anterior aorta, and crosses the root of the posterior 

 aorta to reach the esophagus, to the left and upper side of which 

 it pursues its course as far as the diaphragm. 



Its branches within the chest are — 1. Filaments to the tracheal 

 plexus, consisting of an assemblage and intercommunication of 

 nerves, mostly from the sympathetic, around the lower part of 

 the trachea, within the space between the two first ribs. 2. Two 

 or three smaller branches to the cardiac plexus. 3. A single 

 branch, of considerable importance, denominated the recurrent 

 nerve. 4. Branches to the anterior pulmonary plexus. 5. Re- 

 flected branches to the posterior pulmonary plexus. And, on the 

 right side, in addition to these, the nerve furnishes a still larger 

 branch, which is directed forthwith to the heart : in its passage 

 it subdivides into two chords, and these branch out as they 

 approach the base of the organ, and penetrate the parietes of 

 the auricles. 



