548 



TEXT-BOOK OF PHYSIOLOGY. 



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

 and that they are indeed but aberrant branches of this nerve. 



EIGHTH PAIR. THE AUDITORY. 



The eighth cranial nerve, the auditory, consists of the centrally 

 coursing axons of neurons which connect the essential organ of 



hearing with sensor end-nuclei 

 .x 10 in the pons Varolii. This nerve 



..-'' consists of two portions: viz., a 



cochlear or auditory and a ves- 

 tibular or equilibratory. 



Origin. The axons compris- 

 ing the cochlear portion have 

 their origin in the bipolar nerve- 

 cells of the spiral ganglion located 

 v\ canal near the bnse 



in the SDira 



of the osseous lamina spiralis 

 (Fig. 254). From this origin 

 they pass centrally into the cen- 

 tral 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 

 6 cells pass peripherally to termi- 

 nate on the ciliated epithelial cells 

 of the organ of Corti. 



The axons comprising the 

 vestibular portion have their 

 origin in the bipolar nerve-cells 

 oftEe ganglion ofScarpa located 

 irPtne internal auditory meatus. 

 From thfs origin they pass cen- 

 trally in connection with the 

 cochlear portion. Dendritic pro- 

 cesses from these cells pass per- 

 ipherally into the internal ear, 

 where they terminate on epithe- 

 lial 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 



FIG. 254. ORIGIN AND TERMINATION 

 OF THE AUDITORY NERVE. i. 

 Cochlea. 2. Spiral ganglion (Corti). 

 3. Cochlear nerve. 4. Ventral 

 acoustic nucleus. 5. Lateral acoustic 

 nucleus. 6. Semicircular canals. 7. 

 Ganglion of Scarpa. 8. Vestibular 

 nerve. 9. Dorso-external nucleus 

 (Deiters). 10. Dorso-internal nu- 

 cleus. (After Moral and Doyon.} 



