SENSE AREAS AND ASSOCIATION AREAS. 



199 



been shown to supply, mainly at least, the cochlear portion of the 

 internal ear, and is, therefore, the auditory nerve proper. This 

 division is spoken of as the cochlear branch. The internal root sup- 

 plies mainly the vestibular branch of the internal ear, and is there- 

 fore spoken of as the vestibular branch (see Fig. 89) . It seems cer- 

 tain that the latter is not an auditory nerve, but is concerned 

 with peculiar sensations that have an important influence on mus- 

 cular activity, especially in complex movements. The central 

 course of these two roots is quite as distinct as their peripheral 



Posterior nucleus. 



Deiters's nucleus. 



Dorsal nucleus. 

 Ventral nucleus. 



Cochlear branch. 



Vestibular branch. 



Semicircular 

 canals. 



Scarpa's ganglion. 

 Cochlea. 



Spiral ganglion. 

 Fig. 89. The medullary nuclei of the eighth nerve. (From Poirier and Charpy.) 



distribution, a fact that bears out the supposition that they medi- 

 ate different functions. The central course of the cochlear branch 

 is indicated schematically in Figs. 89 and 90. The fibers con- 

 stituting this branch arise from nerve cells in the modiolus of the 

 cochlea, the spiral ganglion. These cells, like those in the posterior 

 root ganglia, are bipolar. One axon passes peripherally to end around 

 the sense cells of the cochlea, at which point the sound waves arouse 

 the nerve impulses. The other axon passes toward the pons, forming 

 one of the fibers of the cochlear branch. On entering the pons 

 these cochlear branches end in two nuclei, one lying ventral to the 



