620 THE NERVOUS SYSTEM 



pharynx, the tonsils, and posterior palate. Nerves of taste are supplied to 

 the taste buds on the posterior third of the tongue and to the fauces. 



The Tenth Nerve, Vagus or Pneumogastric Nerve. The origin of the 

 vagus nerve is, as we have just seen, situated in the lower half of the floor of 

 the fourth ventricle, figure 378. Its nucleus is said to represent the cells of 

 Clarke's column of the spinal cord. In origin it is closely connected with 

 the ninth, eleventh, and the twelfth. The combined glosso-pharyngeal-vago- 

 accessory nuclei lie outside of, close to, and parallel with the nucleus of the 

 twelfth. There are two main vagal nuclei, one motor, the other sensory. 



Distribution. It has, of all the nerves, the most varied distribution and 

 functions, either through its own filaments, or through those which, derived 

 from other nerves, are mingled in its branches. The vagus supplies sensory 

 branches, which accompany the sympathetic on the middle meningeal 

 artery, which supply the back part of the meatus and the adjoining part 

 of the external ear. It is connected with the petrous ganglion of the glosso- 

 pharyngeal, by means of fibers to its jugular ganglion, with the spinal acces- 

 sory, which supplies it with its motor fibers for the larger and upper portion 

 of the esophagus, and with its inhibitory fibers for the heart; also with the 

 twelfth; with the superior cervical ganglion of the sympathetic; and with the 

 cervical plexus. The parts supplied by the branches of the vagus are as 

 follows: 



1. A large portion of the mucous membrane and some of the muscles 

 of the pharynx are supplied by its pharyngeal branches, through the phar- 

 yngeal plexus. 



2. The mucous membrane of the under surface of the epiglottis, and of 

 the greater part of the larynx, and the crico-thyroid muscle, by the superior 

 laryngeal nerve. 



3. The mucous membrane and muscular fibers of the trachea, the lower 

 part of the pharynx and larynx, and all the muscles of the larynx except the 

 crico-thyroid are supplied by the inferior laryngeal nerve. It also supplies 

 the first segment of the esophagus. 



4. The mucous membrane and muscular coats of the esophagus receive 

 fibers from the esophageal branches. 



5. The branches of the vagus form the supply of nerves to the heart and 

 the great arteries. 



6. The lungs are supplied through the anterior and posterior pulmonary 

 plexuses. 



7. The stomach, the intestines, the spleen, and the liver are supplied by 

 the gastric, splenic, and hepatic vagus branches. 



Functions. Throughout its whole course the vagus contains both sensory 

 and motor fibers. To summarize the many functions of this nerve, which 

 have been for the most part considered in the preceding chapters, it may be 

 said that it supplies, i, motor fibers to the pharynx and esophagus, to the 



