622 THE NERVOUS SYSTEM 



stomach and intestines, to the larnyx, 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 

 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. The 

 fibers from the two origins come together at the jugular foramen, but sepa- 

 rate again into two branches. The inner arises from the medulla and joins 

 the vagus, to which it supplies fibers, consisting of small medulla'ted nerve 

 fibers. The outer consists of large medullated fibers and supplies the tra- 

 pezius 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 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-thy- 

 roid, and omo-hyoid through its descending branch, descendens hypoglossi; 

 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 withdrawn 

 it turns away from the paralyzed side. Occasionally it is not possible 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. 



