FUNCTIONS OF THE COCHLEA 323 



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- 

 dolymph; to their outer ends pass the axis cylinders of the 

 nerve fibers, though the exact mode of connection is not 

 clear. The rod cells are much more numerous than the hair 

 cells, but their precise connection with audition is not ap- 

 parent. 



Upon the basilar membrane are the rods of Corti. They 

 consist of two sets of pillars of varying length, slanting to- 

 ward each other, thus leaving at their base a space which be- 

 comes a canal by a longitudinal succession of these pillars. 

 There are supposed to be about 4,500 elements in the outer 

 and 6,500 in the inner set of these rods. Intimately associ- 

 ated with the pillars are large numbers of hair cells with 

 which the auditory nerve filaments may communicate; it is 

 certain that these filaments are closely connected in some way 

 with the pillars. 



Functions of the Semicircular Canals. The use of these 

 is obscure. Their destruction is not followed by interference 

 with hearing, although auditory filaments are distributed 

 to some parts of them. Curiously enough, however, this 

 lesion is one of the three chief ones interfering so markedly 

 with equilibrium the phenomena following it being not un- 

 like those sequent upon lesions of the cerebellum and the pos- 

 terior white columns of the cord. 



Functions of the Cochlea. While the exact mechanism of 

 the production of auditory impressions is unknown, there 

 seems to be no doubt that such mechanism takes place almost 

 entirely in the cochlea, and that fibers which convey to the 

 auditory centers impressions of sound are distributed to the 



