SyS THE CENTRAL NERVOUS SYSTEM 



The seventh nerve is not purely motor. From the cells of a ganglion 

 on it corresponding to a spinal ganglion (the geniculate ganglion) 

 afferent fibres arise, which pass in the pars intermedia or nerve of 

 Wrisberg into the pons between the seventh and eighth nerves, and 

 there bifurcate into ascending and descending branches, like other 

 afferent fibres originating in ganglia of the spinal type. The descend- 

 ing branches enter the fasciculus solitarius, and end by arborizing 

 around 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 



viil 



Fig. 362. Scheme of Path of Auditory Impulses (Lewandowsky). 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, posterior corpora 

 quadrigemina, with Cq, their commissure, and Bq, the brachia; Gm, mesial or 

 internal geniculate body; R, cerebral cortex. 



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 nerve, but, unlike them, they 

 remain, even in mammals, bipolar throughout life. Their central 

 processes form the axons of the eighth nerve. Their peripheral pro- 

 cesses 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 auditorv 



