THE AUTONOMIC SYSTEM 663 



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, apparently, by branches of the vagus, are said to derive 

 their motor nerves from the accessory; and Vrolik makes the very signifi- 

 cant 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 omo-hyoid through its descending branch, descendens hypo- 

 glossi; the thyro-hyoid through a special branch; and the genio-hyoid, 

 stylo-glossus, hyo-glossus, and genio-hyoglossus and linguales through its 

 lingual branches. 



Functions. The function of the hypoglossal is exclusively motor. In 

 cases of hemiplegia involving the functions of the hypoglossal nerve the 

 tongue when protruded deviates toward the paralyzed side, when with- 

 drawn it turns away from the paralyzed side. Occasionally it is not pos- 

 sible to observe any deviation in the direction of the protruded tongue; 

 probably because the tongue is so compact and firm that the muscles on 

 either side can push it straight forward or turn it for some distance toward 

 either side. In hypoglossal paralysis from cerebral lesions or lesions of the 

 peduncles the paralysis is contralateral. 



THE AUTONOMIC SYSTEM. 



In the introductory statement of this chapter we emphasized the fact 

 that the outlying anatomical nerve divisions long known as the sympa- 

 thetic system is an organic and constituent part of the general nervous 

 system. Histologically there is close relation of the constituent parts, 

 embryonically there is a common origin of the neurones, and physio- 

 logically the mechanisms are dependency related. The main portion of 

 this group of neurones we discuss under the title The Autonomic System. 



