THE SENSES 



come more oblique; in other words, the tunnel becomes wider, but diminishes 

 in height as we approach the apex of the cochlea. 



Leaning against the rods of Corti and apparently supported by them 

 are sensory cells or hair cells. The hair cells are in two series, the inner and 

 the outer hair cells. The former consist of a single layer, the latter of three 

 or four layers, figure 438. There are two additional types of supporting cells, 

 the cells of Deiters and of Hensen. The whole structure when viewed from 

 above bears a remarkable resemblance to the keyboard of a piano. 



The cochlear division of the auditory nerve enters the base of the modiolus 

 and sends a spiral whorl of fibers out under the spiral lamina The gan- 



FIG. 437- Semidiagrammatic Section of a Cochlear Whorl. (After Heitemann.) 



glionic cells of the cochlear division of the auditory nerve are located in the 

 base of the lamina where they form the spiral ganglion. The nerve fibers 

 from the ganglion cells pass out through small holes in the periphery of the 

 spiral plate of bone, to enter the organ of Corti. Here they form small longi- 

 tudinal bundles that quickly end about the hair cells. 



THE PHYSIOLOGY OF HEARING. 



All the acoustic contrivances of the organ of hearing are means for con- 

 ducting sound. Since all matter is capable of propagating sonorous vibra- 

 tions, the simplest conditions must be sufficient for mere hearing; since all 

 substances surrounding the auditory apparatus would stimulate it. The com- 

 plex development of the organ of hearing, therefore, must have for its object 



