CEREBELLUM, PONS, AND MEDULLA. 249 



and the fibers ending in them constitute the descending spinal root 

 of the fifth nerve (see Fig. 106). 



The Sixth Cranial Nerve (N. Abducens). This nerve arises from 

 the base of the brain at the posterior edge of the pons. It is a motor 

 nerve, and supplies fibers to the external rectus muscle of the eye- 

 ball. In the interior of the brain its fibers originate in a small spheri- 

 cal nucleus lying beneath the floor of the fourth ventricle. Con- 

 nections have been traced between this nucleus and the pyramidal 

 tract of the opposite side (Fig. 106). 



The Seventh Cranial Nerve (N. Facialis) . This nerve appears 

 on the base of the brain at the inferior margin of the pons, lateral 

 and somewhat posterior to the emergence of the sixth nerve. It 

 is mainly a motor nerve, but carries some sensory fibers (fibers of 

 taste and general sensibility) received through the n. intermedius of 

 Wrisberg. The motor fibers of the nerve supply the muscles of the 

 face, part of the scalp, and the ear, including its intrinsic muscles, 

 and in addition secretory fibers are supplied to the submaxillary 

 and sublingual glands. Within the brain these fibers arise from a 

 conspicuous nucleus in the tegmental region of the pons lying 

 ventral to the nucleus of the sixth, beneath the middle of the fourth 

 ventricle (Fig. 106) . The sensory fibers of the nerve of Wrisberg 

 originate in the nerve cells of the geniculate ganglion. 



The Ninth Cranial Nerve (N. Glossopharyngeus) arises from the 

 side of the medulla, the restiform body. It is a mixed nerve, 

 supplying motor fibers to the muscles of the pharynx and the base 

 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 

 cinerea. 



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 



