THE VAGUS NERVE. 



1267 



neck it leaves the carotid sheath and becomes an occupant of the thorax. Entering 

 the thora.cic cavity the nerve traverses first the superior and then the posterior 

 mediastinum, its course differing widely on the two sides. 



The right vagus (Fig. 1090), after passing in front of the first portion of the 

 subclavian artery and behind the right innominate vein and the superior vena cava, 

 descends along the right side of the trachea to reach the posterior aspect of the root 

 of the lung. Here the entire nerve breaks up to form the posterior pulmonary 

 plex2is, which assembles at its lower border to form two cords. These pass inward 

 across the vena azygos to the oesophagus and again break up to unite with a 

 similar contribution from the left side to form the (esophageal plexus (Fig. 108 1). 

 On approaching the oesophageal opening in the diaphragm, the fibres of the plexus 

 become reunited to form the continuation of the trunks of the two vagus nerves. 

 The right vagus, somewhat larger than the left, follows the posterior aspect of the 

 oesophagus and, after entering the abdomen through the oesophageal opening, is 



Fig. 1077. 



Diagram showing connections between the superior cervical sympathetic ganglion and the glosso-pharyngeal, vagus 



and hypoglossal nerves. 



distributed to the posterior surface of the stomach and to the solar plexus, and 

 indirectly to the spleen, pancreas, intestine, kidney and suprarenal body. 



The left vagus, after passing between the left common carotid and subclavian 

 arteries and behind the left innominate vein, crosses the anterior surface of the aorta 

 and then bends backward to reach the posterior surface of the root of the lung. In 

 a manner similar to the right, it forms the posterior pulmonary plexus and reassem- 

 bles into two cords. These pass inward anteriorly to the thoracic aorta and 

 enter the ccsophageal plexus, at the lower end of which the fibres of the left nerve 

 gather on the anterior surface of the oesophagus, traverse as a single solid trunk 

 the oesophageal opening and are distributed to the anterior surface of the stomach 

 and to the liver. 



Ganglia of the Vagus Nerve. — Two ganglia are found in the course of the 

 nerve, the ganglion of the root and the ganglion of the tr^ink. They are collections 

 of neurones whose axones form the sensory root-fibres of the vagus, the greater 

 number, however, being connected with the cells of the ganglion of the root. 



The ganglion of the root (g. jugulare) or upper ganglion (Fig. 1077) is 

 a grayish spherical mass of nerve-cells, about 4 mm. in length, situated in the upper 

 part of the jugular foramen. 



