THE ENCEPHALIC OR CRANIAL NERVES 631 



through the chorda tympani, along the facial nerve as far as the geniculate 

 ganglion. The exact pathway for these afferent or gustatory fibers beyond the 

 geniculate ganglion has long been a subject of much discussion. According 

 to some observers these fibers enter the great petrosal nerve, pass forward as 

 far as the spheno-palatine ganglion, then into the superior maxillary division 

 of the trigeminal, and so to the brain. According to others, these fibers 

 pass into the pars intermedia, into the pons, where they terminate around 

 the sensor end-nucleus of .the glosso-pharyngeal. The evidence for and 

 against either of these two views is most conflicting and insufficient to justify 

 positive statements one way or the other. To the writer the weight of evi- 

 dence seems to favor the view that the gustatory fibers have their origin in the 

 geniculate ganglion; that they pass centrally through the pars intermedia; 

 that they are similar in function to the glosso-pharyngeal; and that they are 

 indeed but aberrant branches of this nerve. 



THE EIGHTH NERVE. THE ACOUSTIC 



The eighth cranial nerve, the acoustic, consists of the centrally coursing 

 axons of neurons which connect the essential organ of hearing with sensor 

 end-nuclei in the pons Varolii. This nerve consists of two portions: viz., 

 a cochlear or auditory and a vestibular or equilibratory. 



Origin. The axons comprising the cochlear portion have their origin 

 in the bipolar nerve-cells of the spiral ganglion located in the spiral canal near 

 the base of the osseous lamina spiralis (Fig. 271). From this origin they 

 pass centrally into the central canal of the modiolus, at the base of which 

 they emerge in well-defined bundles and enter the internal auditory meatus. 

 Dendritic processes from these cells pass peripherally to terminate on the 

 ciliated epithelial cells of the organ of Corti. 



The axons comprising the vestibular portion have their origin in the 

 bipolar nerve-cells of the ganglion of Scarpa located in the internal auditory 

 meatus. From this origin they pass centrally in connection with the cochlear 

 portion. Dendritic processes from these cells pass peripherally into the 

 internal ear, where they terminate in the epithelial cells situated on the inner 

 surface of the utricle and saccule and in the ampullae of the semicircular 



canals. , , 



The common trunk of the auditory nerve, consisting of both cochlear 

 and vestibular divisions after emerging from the internal auditory meatus, 

 passes backward, inward, and downward as far as the lateral aspect of the 

 pons where the two divisions again separate. 



The cochlear nerve, the external root, passes to the outer side of the 

 restiform body and enters the ventral acoustic nucleus and tfie lateral acous- 

 tic nucleus, around the cells of which its end-tufts arborize. The vestib- 

 ular nerve, the internal root, passes on the inner side of the restiform body 

 to the dorsal portion of the pons, where, after bifurcating, the end-tufts of 

 the axons arborize around the dorso-internal or chief auditory nucleus and 

 the dorso-external or Deiters' nucleus. Some of the fibers of the vestibu- 

 lar branch descend through the pons and medulla as far as, the cuneat( 



Cortical Connections. From the nerve-cells of the ventral and lateral 

 acoustic nuclei axons arise, some of which cross the median plane to enter 



