TERMINATION OF AUDITORY NERVE 321 



The basilar membrane completes the septum and divides the 

 lumen of the cochlea into two canals, the scala tympani and 

 the scala vestibuli, corresponding in name to the tympanic 

 and vestibular openings of the cochlea. The semicircular 

 canals, three in number superior, external and posterior de- 

 scribe arches from the posterior aspect of the vestibule, com- 

 municating by both their extremities with that cavity. 



The membranous labyrinth consists of a special membrane 

 lying inside the bony labyrinth and corresponding in general 

 outline to the walls of the cavity. It is, however, separated from 

 the walls by perilymph, and encloses a similar fluid, the en- 

 dolymph. It covers the sides of the lamina spiralis in the cochlea 

 and completes the septum, besides following the wall proper; 

 and on one side it sends a distinct process from the tip of the 

 a mina spiralis to the wall of the canal, so that there are in reality 

 three divisions of the lumen of the cochlea. This process is the 

 membrane of Reissner, and the third canal is the scala media 

 the true membranous cochlea. (See Fig. 91.) 



Termination of Auditory Nerve. The membranous laby- 

 rinth, containing and being suspended in fluid, receives the term- 

 inal filaments of the eighth nerve as well as all the sonorous vibra- 

 tions intended for that nerve. When the auditory nerve has 

 reached the base of the internal auditory meatus it enters the 

 internal ear by two divisions, one for the vestibule and semicir- 

 cular canals and the other for the cochlea. The vestibular 

 portion again subdivides, sending one branch to the utricle and 

 superior and horizontal semicircular canals, and another to the 

 saccule and posterior semicircular canal. The fibers of the 

 eighth nerve spread out over the inner surface of the membrane 

 to end in a way somewhat obscure. The membrane is lined 

 internally by epithelium whose character differs in different areas. 

 In the region of distribution of the vestibular portion of the nerve 

 the cells are of two kinds, hair cells and rod cells. From the 

 inner ends of the hair cells ciliated processes project into the en- 



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