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THE NERVOUS SYSTEM 



on the middle meningeal artery supplying 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 and with the spinal accessory which con- 

 tributes motor fibers for the larger and upper portion of the esophagus, 

 and inhibitory fibers for the heart. It is connected also with the twelfth; 

 with the superior cervical ganglion of the sympathetic; and with the cer- 

 vical plexus. The organs 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 

 pharyngeal 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 re- 

 ceive fibers from the esophageal branches. 



5. The branches of the vagus form the supply of inhibitory nerves to 

 the heart and the sensory distribution of depressor fibers to the great 

 arteries. 



6. The sensory fibers of the lungs and the bronchial muscle motor 

 nerves 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 sen- 

 sory 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 esopha- 

 gus, to the stomach and intestines, to the larynx, trachea, bronchi, and 

 lungs; 2, sensory fibers to the same regions; 3, inhibitory fibers to the heart; 

 4, inhibitory afferent fibers, i.e., depressors, to the vaso-motor center. 



Surgical division of both vagi or of both their recurrent branches is 

 often ultimately fatal in young animals; but in old animals the division of 

 the recurrent nerve is not generally fatal, and that of both the vagi, even, 

 is not always fatal. 



The Eleventh Nerve, or Spinal Accessory. This nerve arises by two 

 nuclei, one the nucleus ambiguus from a center in the floor of the fourth 

 ventricle, partly but chiefly in the medulla and continuous with the glosso- 

 pharyngeal- vagus nucleus; the other, from the outer side of the anterior 

 cornu of the spinal cord as low down as the fifth or sixth cervical nerve. 



