212 



PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



quite as distinct as their peripheral distribution, — a fact that bears 

 out the supposition that they mediate different functions. The 

 vestibular branch ends in the nucleus of Deiters, the nucleus of 

 Bechterew, and the nucleus fastigii of the cerebellum. Through 

 these nuclei reflex connections are made with the motor centers 

 of the cord and midbrain, and probably also with the cerebellum. 

 The path is not known to be continued forward to the cerebrum. 

 The central course of the cochlear branch is indicated schematically 



in Figs. 94 and 95. The 

 ^ fibers constituting this 



branch arise from nerve 

 cells in the modiolus of 

 the cochlea, — the spiral 

 ganglion. These cells, 

 like those in the poste- 

 rior root ganglia, are bi- 

 polar. One axon passes 

 peripherally to end 

 around the sense cells 

 of the cochlea, at which 

 point the sound waves 

 arouse the nerve im- 

 pulses. 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 res- 

 tiform body and known 

 as the ventral or acces- 

 sory nucleus (V.n., Fig. 

 •95), and one dorsally, known as the dorsal nucleus or the tuber- 

 culum acusticum (D.n.). From these nuclei the path is continued 

 by secondary sensory neurons, and its further course toward the 

 brain is still a matter of much uncertainty in regard to many 

 of the details.* The general couree of the fibei-s, however, is 

 known. Those axons that arise from the accessory or ventral 

 nucleus pass mainly to the opposite side by shghtly different routes 

 (Fig. 95). Some strike directly across toward the ventral side of 

 the pons, forming a conspicuous band of transverse fibers that 

 has long been known as the corpus trapezoideum; othere pass 

 dorsally around the restiform body and then course downward 



* For literature, see Van Gehuchten, "Le Nevraxe," 4, 253, 1903, and 

 8, 127, 1906. 



Fig. 96. — Diagram to show central course of 

 •auditory fibers (modified from Van Gehuchten): 

 D.n., I)orsal nucleus giving rise to the fibers that 

 form the medullary stria (a.s.); V.n., the ventral 

 nucleus, giving origin to the fibers of the corpus 

 trapezoideum (dr.); s.o., superior olivary nucleus; 

 ■l.f., lateral lemniscus; n.s., nucleus of the lateral 

 lemniscus; t.g.i.,, the inferior colliculus. 



