HEARING 349 



ear, the stapes is slightly but powerfully pressed into the perilymph of 

 the scala vestibula through the fenestra ovalis. The pressure is almost 

 instantly communicated to the very thin and elastic Reissner's membrane 

 and passes into the endolymph of the scala media (containing Corti's 

 organ), through it, and into the perilymph of the scala tympani below. 

 As it passes through the membrana basilaris (bearing the organ of Corti), 

 it causes to vibrate that particular transverse fiber of this continuous 

 membrane which corresponds by its length most exactly to the vibration- 

 number of the original producer of the sound. This fiber of the mem- 

 brana basilaris (more or less accompanied by several fibers on either 

 side), rises slightly and with it rise the pillars of Corti and the hair-cells 

 attached to them above. 



As to what happens further than this there is a still greater disagree- 

 ment of opinion. Perhaps these cells are pressed against the mem- 



FIG. 201 



Organ of Corti : gl, ganglion; SP, nerve-fibers; CC, Corti's canal; I, l f , laminae basilares; SZ.V, 

 hearing cells; V, supporting cells; mt, membrana tectoria; cr, cresta spiralis. (B. Haller.) The 

 membrana reticularis (just over the hair-cells) is not shown. This diagram represents one out of 

 several theories of the organ's structure and action. One chief doubt is as to whether the hairs 

 of the hair-cells (SZ) are continuous with the fibers of the membrana tectoria, mt. 



brana tectoria, the latter then either damping the vibrations of their 

 filaments or pressing them downward against the nerve-fibrils below. 

 Perhaps the membrana tectoria is the vibrating part of the organ. 

 Perhaps it is the filaments only of the hair-cells which vibrate, or even 

 the rods only. One or two experts have claimed that the ligamentum 

 spirale (by which the membrana basilaris is attached to the outer wall 

 of the cochlea) contains muscle-cells, and that therefore it probably 

 serves to tighten the transverse fibers of that membrane. Much of 

 importance remains to be learned about the auditory hair-cells especially, 

 not only as to their filaments but as to their very complicated internal 

 structure. About the function of the pillars of Corti and the tunnel 

 between them information is also sorely needed before any satisfactory 

 theory of the organ of Corti can be suggested. In all these parts (and in 

 many others we have not even named here) there is a mechanism whose 



