246 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



of the tongue and secretory fibers to the parotid gland. Within 

 the brain these fibers arise from two motor nuclei common to this 

 and the tenth nerve, — namely, a dorsal nucleus below the floor of 

 the fourth ventricle and a smaller ventral nucleus, n. ambiguus, 

 in the reticular substance of the tegmentum (Fig. 106). The sensory 

 fibers supply in part the mucous membrane of the tongue and 

 pharynx, the tympanic cavity, and the Eustachian tube. These 

 fibers arise from cells in the two ganglia on the trunk of the nerve, 

 the ganglion superius and g. petrosum. The branches from these 

 cells that pass into the medulla terminate in the nucleus of the ala 

 ciuerea. 



The Tenth Cranial Nerve (N. Vagus or Pneumogastricus) . — This 

 nerve arises from the side of the medulla posterior to the origin of 

 the glossopharyngeal nerve. It is also a mixed nerve, with an 

 extensive distribution to the respiratory and digestive organs and 

 the heart. Its efferent or motor fibers arise within the brain from 

 the same masses of cells that give rise to the motor fibers of the 

 glossopharyngeal. These fibers supply the intrinsic muscles of the 

 larynx, esophagus, stomach, small intestine, and part of the large 

 intestine. Inhibitory fibers are carried to the heart and secretory 

 fibers to the gastric and pancreatic glands. Its sensory or afferent 

 fibers are distributed to the mucous membrane of the larynx, 

 trachea, and lungs, and to the mucous membrane of the esophagus, 

 stomach, intestines, and gall-bladder and ducts. These fibers 

 arise from cells in the gangha on the tnmk of the nerve, the gan- 

 glion jugulare and g. nodosum. The branches from these cells that 

 pass into the medulla terminate in the gray matter of the ala cinerea. 



The Eleventh Cranial Nerve (N. Acccssorius) . — This nerve is 

 usually described as arising by upper roots from the medulla, and 

 by a series of lower roots from the spinal cord as low as the fifth 

 to the seventh cervical segment. It is a motor nerve, supplying 

 fibers to the sternomastoid and trapezius muscles. The medullary 

 branches arise from the posterior portion of the dorsal motor 

 nucleus which gives origin to the vagus, while the spinal branches 

 originate from cells in the anterior horn of the gray matter of the 

 cord (Fig. 106). 



The Twelfth Cranial Nerve (N. Hypoglossus) . — This nerve arises 

 from the medulla in the furrow between the anterior pyramid and 

 the olivary body. It is a motor nerve, supplying the muscles of 

 the tongue and the extrinsic muscles of the larynx and hyoid bone. 

 Within the brain these fibers originate from a distinct nucleus 

 lying in the floor of the fourth ventricle near the mid-line (Fig. 

 106). 



