CRANIAL NERVES. 



837 



TENTH PAIR, PNEUMOGASTRIC, OR VAGUS. 



Of all of the cranial nerves, the vagus is the most important 

 and has the most functions of a varied nature in clinical study. It 

 is a nerve of motion and sensation. 



Cortical Connection. The motor path to the nucleus of the 

 vagus is from the inferior part of the central convolutions. 



The motor neuraxons arise from the nucleus ambiguus. The 

 sensory roots co.me from the neuraxons of the jugular and petrosal 

 ganglions. The sensory neuraxons have been described under the 

 preceding nerve: the glosso-pharyngeal. The vagus springs by 

 means of from ten to fifteen cords from the groove behind the olivary 

 body and passes through the jugular foramen with the glosso-pharyn- 

 geal and spinal accessory nerves. In the jugular foramen it has a 

 ganglion : the jugular ganglion. After it emerges from the foramen 

 it has an enlargement, the gangliform plexus, or ganglion nodosum. 



The plexus gives of? the pharyngeal and superior laryngeal nerves. 



The pharyngeal nerves, three in number, go down the side of 

 the pharynx to supply the mucous membrane and muscles of the 

 pharynx. The superior laryngeal goes down the side of the larynx. 

 This nerve also furnishes a collateral branch, important from a phy- 

 siological standpoint, to the crico-thyroid muscle. It then loses 

 itself in the mucous membrane of the larynx. 



At the base of the neck the vagus gives off another branch, the 

 recurrent, or inferior laryngeal. The nerve upon the right side 

 descends in front of the subclavian artery and winds around it pos- 

 teriorly from beneath. Upon the left side the nerve winds around 

 the arch of the aorta in the same manner. 



As collateral branches, the vagus furnishes cardiac fibers, which 

 form the cardiac plexus and are destined to innervate the heart. 

 There are also cesophageal fibers whose terminations are distributed 

 to the oesophagus and trachea. 



In the cervical region the tenth pair gives rise to a branch, the 

 nervus depressor. It results by the fusion of two fibers: one from 

 the superior laryngeal and the other from the vagus itself. The 

 nervus depressor loses itself 'in the cardiac tissue of the heart at 

 the level of the aortic and pulmonary orifices. 



During the first portion of its course the vagus forms numerous 

 anastomoses. These are with the spinal accessory, the facial, and 

 hypoglossal cranial nerves and with a great number of branches from 

 the various ganglia of the sympathetic system. 



