THE CRANIAL NERVES. 227 



internal auditory meatus after which it passes backward and inward 

 as far as the lateral aspect of the pons, where the two main divisions 

 again separate. The cochlear portion passes to the outer side of the 

 restiform body ; the vestibular portion passes to the inner side of the 

 restiform body to the dorsal portion of the pons. After entering the 

 pons the fibers composing both portions come into histologic rela- 

 tions with different groups of nerve-cells. 



Properties. Stimulation of the cochlear nerve is unattended by 

 either motor or sensor phenomena. Division of the nerve is followed 

 by a loss of hearing. Destruction of the semicircular canal, involving 

 a lesion of the vestibular nerves at their origin, is followed by a 

 loss of the power of coordination and equilibration. 



Functions. The cochlear nerve presides over the sense of hearing. 

 It carries to the brain the nerve impulses produced by the impact of 

 atmospheric vibrations on the ear, and which give rise to the sen- 

 sation of sound. The vestibular nerve carries nerve impulses to 

 the brain, which excite certain reflex adaptive movements by which 

 the equilibrium of the body is maintained. 



Ninth Pair. Glossopharyngeal. 



Origin. From nerve-cells in the ganglia situated on the trunk 

 of the nerve near the medulla oblongata viz., the petrosal ganglion 

 and the jugular ganglion. From these cells a single branch emerges, 

 which soon divides into two branches, one of which passes centrally, 

 the other peripherally. The centrally directed branches enter the 

 medulla oblongata, where they terminate around nerve-cells. The 

 peripherally directed branches collectively form the two main di- 

 visions from which the nerve takes its name. 



The glossopharyngeal also contains efferent nerve-fibers, which 

 have their origin in nerve-cells beneath the floor of the fourth 

 .ventricle. 



Distribution. The trunk of the nerve passes downward and for- 

 ward, receiving near the jugular ganglion fibers from the facial and 

 pneumogastric nerves. It divides into two large branches, one of 

 which is distributed to the base of the tongue, the other to the 

 pharynx. In its course it sends filaments to the otic ganglion ; a 

 tympanic branch which gives sensibility to the mucous membrane of 

 the fenestra rotunda, fenestra ovalis, and Eustachian tube ; lingual 



