THE CENTRAL NERVOUS SYSTEM 



823 



nerve-cells in the upper part of that bundle. The peripheral axons 

 of the nerve-cells in the geniculate ganglion enter the large super- 

 ficial petrosal nerve and the chorda tympani, in which they, or 

 some of them, perhaps represent taste fibres. 



The eighth or auditory nerve enters the medulla oblongata by two 

 roots (a dorsal and a ventral), one of which passes in on each side 

 of the restiform body. The cells of origin, both of the dorsal and 

 of the ventral root, are situated in the internal ear, the former in 

 the ganglion spirale, or ganglion of Corti, which is embedded in the 

 bony spiral of the cochlea, the latter in the ganglion vestibulare, 

 or ganglion of Scarpa, which lies in the vestibule. These cells 

 correspond to the ganglion cells on the posterior root of a spinal 



VIII 



FIG. 344. SCHEME OF PATH OF AUDITORY IMPULSES (LEWAXDOWSKY). 



Sp, ganglion spirale ; G, accessory nucleus ; T, acoustic tubercle ; Tr, trapezium ; 

 H, Held's fibres ; St, striae acusticae ; tr, trapezoid nucleus ; Os, upper olive ; 

 LI, lateral fillet, with its nucleus, nL ; P, commissure of the lateral fillets ; Qp, pos- 

 terior corpora quadrigemina ; with Cq, their commissure, and Bq, the brachia ; 

 Gin, mesial or internal geniculate body ; R, cerebral cortex. 



nerve, but, unlike them, they remain, even in mammals, bipolar 

 throughout life. Their central processes form the axons of the 

 eighth nerve. Their peripheral processes are distributed in the case 

 of the dorsal root to the organ of Corti, in the case of the ventral 

 root to the semicircular canals and the vestibule. For this reason 

 the dorsal root is often called the cochlear division, and the ventral 

 root the vestibular division of the auditory nerve. And the cochlear 

 and vestibular roots are physiologically as well as anatomically 

 distinct. For (p. 958) the cochlea subserves the function of 

 hearing, the semicircular canals and vestibule the function of 

 equilibration. As they enter the medulla oblongata, the fibres of 

 the dorsal root bifurcate. Of the two branches, one is considerably 



