560 THE NERVOUS SYSTEM 



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 inhibitory 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 

 stomach and intestines, to the larynx, trachea, bronchi, and lungs; 2, sensory 

 and, in part, 3, vaso-motor fibers to the same regions; 4, inhibitory fibers 

 to the heart; 5, inhibitory afferent fibers to the vaso-motor center. 



Division of both vagi or of both their recurrent branches is often quickly 

 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 ventri- 

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

 geal-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. The fibers from 

 the two origins come together at the jugular foramen, but separate again into 

 two branches. The inner arises from the medulla and joins the vagus, to 

 which it supplies fibers, consisting of small medullated nerve fibers. The 

 outer consists of large medullated fibers and supplies the trapezius and sterno- 

 mastoid muscles. The muscles of the larynx, all of which are supplied, ap- 

 parently, by branches of the vagus, are said to derive their motor nerves from 

 the accessory; and Vrolik makes the very significant statement that in the 

 chimpanzee the internal branch of the accessory does not join the vagus at 

 all, but goes direct to the larynx. 



The Twelfth Nerve, or Hypoglossal. Origin and Connections. The 

 nerve arises from a large-celled and very long nucleus in the bulb, extending 

 from the floor of the fourth ventricle to the level of the olivary bodies close to the 

 mid-line and inside the nucleus ambiguus. Fibers from this nucleus run from 

 the ventral surface through the reticular formation in a series of bundles 

 passing between the olivary nucleus laterally and the pyramid and accessory 

 olive medially, to gain the ventral surface. The nerve emerges from a groove 

 between the pyramid and olivary body. The fibers of origin are continuous 

 with the anterior roots of the spinal nerves. 



This nerve is the motor nerve to the muscles connected with the hyoid bone, 

 including those of the tongue. It supplies the sterno-hyoid, sterno-thyroid, and 



