Hearing, and the Ear. 461 



covered by epithelial cells which connect by fibres with the prolongation 

 of the arch fibres at the top of the arches. A branch of the auditory nerve 

 runs up the cavity in the center of the modiolus. The central part of 



FIG. 198 .A Single pair of the Organs of 



Corti. 



i, Inner fibre ; next the modiolus. 

 e. Outer fibre. 

 ^. Connection and prolongation of the 



fibres at the top. 



FIG. 199 .B Five Organs of Corti as they 

 stand together oh the Basilar mem- 

 brane. 



i and e. Inner and outer fibres. 



b. Basilar membrane. 



(Bernstein,) 



the modiolus is pierced, laterl}', by numerous foramina or minute holes, 

 through which fibers from the nerve penetrate and reach the basilar 

 membrane and the epithelial cells thereon and the arches. 



It is generally admitted that the sensations of noises without regard 

 to tone are produced through the action of the endolymph in the 

 labyrinth in connection with the movement of 

 the otoliths and the filaments on the crista 

 acustica. These delicate organs respond faith- 

 fully to the impulses reaching them from with- 



FIG. 200. Top view of the Kccde showing two arches of 

 Corti on the right. On the left they are removed and 

 the arrangement of nerves and cells beneath them is 

 shown. 



a. Inner Fibres of Corti next to the modiolus. 



e Outer Fibres of Corti. 



/.Their junction at the top. 



1 Their attachment to basilar membrane. 



m n o and all similar parts of the fig. represent spaces, 

 and the alternating parts are nervous connecting ele- 

 ments with nerve fibres extending inwards towards 

 the modiolus. ^ 



P Q- Square terminal formations. 



out, by peculiar and varied movements in an- 

 swer to the peculiar nature of the irritating 

 noise, whether smooth and continuous, inter- 

 rupted and jerky, loud or soft. But it is be- 

 lieved by investigators that it is the office of the organs of the basilar 

 membrane, including the arches of Corti, to receive the impulses which 

 give the sensation of pitch and tone. 



The arches of corti are like so many resonators, (see chap. 39,) and 

 when a sound is carried to them through the endolymph of the scala 

 media, the particular arch susceptible to the agitation accompanying 

 that sound will be stimulated and transfer its stimulation to its fibre of 

 the auditory nerve. If the sound is a compound one, as nearly all mu- 

 sical sounds are, each simple sound and harmonic composing it will find 

 and agitate the arch corresponding to it, and so when all the stimuli 



FIG. 200. 



