628 CRANIAL NERVES. 



cervical. In the occipital triangle it joins with the second and third cervical 

 nerves, and assists in the formation of the cervical plexus, and occasionally of 

 the great auricular nerve. On the front of the Trapezius, it is reinforced bv 

 branches from the third, fourth, and fifth cervical nerves, joins with the poste- 

 rior branches of the spinal nerves, and is distributed to the Trapezius, some 

 filaments ascending and others descending in the substance of the muscle as far 

 as its inferior angle. 



The Pneumogastric Nerve (nervus vagus, or par vagum), one of the three 

 divisions of the eighth pair, has a more extensive distribution than any of the 

 other cranial nerves, passing through the neck and thorax to the upper part of 

 the abdomen. It is composed of both motor and sensitive filaments. It sup- 

 plies the organs of voice and respiration with motor and sensitive fibres ; and 

 the pharynx, oesophagus, stomach, and heart with motor influence. Its super- 

 ficial origin is by eight or ten filaments from the lateral tract immediately 

 behind the olivary body and below the glosso-pharyngeal ; its fibres may, how- 

 ever, be traced deeply through the fasciculi of the medulla, to terminate in a 

 gray nucleus near the lower part of the floor of the fourth ventricle. The 

 filaments become united, and form a flat cord, which passes outwards across 

 the flocculus to the jugular foramen, through which it emerges from the cranium. 

 In passing through this opening, the pneumogastric accompanies the spinal 

 accessory, being contained in the same sheath of dura mater with it, a mem- 

 branous septum separating it from the glosso-pharyngeal, which lies in front. 

 The nerve in this situation presents a well-marked ganglionic enlargement, 

 which is called ganglion jugulare, or the ganglion of the root of the pneumogastric ; 

 to it the accessory part of the spinal accessory nerve is connected. After the 

 exit of the nerve from the jugular foramen, a second gangliform swelling is 

 formed upon it, called the ganglion inferius, or the ganglion of the trunk of the nerve; 

 below which it is again joined by filaments from the accessory nerve. The 

 nerve passes vertically down the neck within the sheath of the carotid vessels, 

 lying between the internal carotid artery and internal jugular vein as far as 

 the thyroid cartilage, and then between the same vein and the common carotid 

 to the root of the neck. Here the course of the nerve becomes different on the 

 two sides of the body. 



On the right side, the nerve passes across the subclavian artery between it 

 and the subclavian vein, and descends by the side of the trachea to the back 

 part of the root of the lung, where it spreads out in a plexiform network 

 (posterior pulmonary), from the lower part of which two cords descend upon 

 the oesophagus, on which they divide, forming, with branches from the opposite 

 nerve, the cesophageal plexus ; below, these branches are collected into a single 

 cord, which runs along the back part of the oesophagus, enters the abdomen, 

 and is distributed to the posterior surface of the stomach, joining the left side 

 of the cceliac plexus, and the splenic plexus. 



On the left side, the pneumogastric nerve enters the chest between the left 

 carotid and subclavian arteries, behind the left innominate vein. It crosses the 

 arch of the aorta, and descends behind the root of the left lung and along the 

 anterior surface of the oesophagus to the stomach, distributing branches over 

 its anterior surface, some extending over the great cul-de-sac, and others along 

 the lesser curvature. Filaments from these latter branches enter the gastro- 

 hepatic omentum, and join the left hepatic plexus. 



The ganglion of the root is of a grayish color, circular in form, about two 

 lines in diameter, and resembles the ganglion on the large root of the fifth nerve. 

 Connecting branches. To this ganglion the accessory portion of the spinal 

 accessory nerve is connected by several delicate filaments ; it also has an anas- 

 tomotic twig with the petrous ganglion of the glosso-pharyngeal, with the facial 

 nerve by means of the auricular branch, and with the sympathetic by means 

 of an ascending filament from the superior cervical ganglion. 



The ganglion of the trunk (inferior) is a plexiform cord, cylindrical in form, 



