322 THE SENSES 



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 apparent. 



Upon the basilar membrane are the rods of Corti. They con- 

 sist of two sets of pillars of varying length, slanting toward each 

 other, thus leaving at their base a space which becomes a canal 

 by a longitudinal succession of these pillars. There are sup- 

 posed to be about 4,500 elements in the outer and 6,500 in the 

 inner set of these rods. Intimately associated 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 unlike those sequent upon 

 lesions of the cerebellum and the posterior 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 cen- 

 ters impressions of sound are distributed to the organ of Corti 

 therein. That is to say, loss of the sense of hearing supervenes 

 upon destruction of this part of the internal ear. In physics it 

 is known that for a sound, for example of a piano string, to be 

 heard the membrana tympani must vibrate in unison with the 

 sonorous vibrations of the cord; that is, "consonating bodies" 

 repeat sonorous vibrations, giving them their proper pitch and 

 quality. It has been supposed that the thousands of rods of 

 Corti, of varying length and size, in the Cochlea are made to 



