A NEW THEOEY OF HEABING. 333 



its course — we are again driven by the difficulties of trie 

 physical problem to base an estimate on physiological 

 considerations : what that estimate is will appear later. 



The cochlear canals, however, are not only tapered but 

 but also spirally coiled ; and the basilar membrane is at 

 the apex continued into the Reissnerian which runs from 

 this point to the base of the spiral narrowing very gradually. 

 When the wave reaches the apex of the cochlea it will pass 

 on to the upper (Reissnerian) membrane, for at this point 

 the lower canal is continuous through the helicotrema 

 with the upper (scala vestibuli) ; and the middle canal ends 

 blindly in the slightly dilated "lagena," the wall of which 

 is formed by the two membranes (upper and lower) which 

 are here continuous with each other. 



The wave of the basilar will thus, starting from the 

 base of the cochlea close to the fenestra rotunda, run 

 forwards to the apex, round the wall of the lagena and 

 down by the Reissnerian membrane to the base of the 

 cochlea. 



The elasticity of the Reissnerian membrane being much 

 less than that of the basilar, it appears certain that the 

 displacement at each point will be greater than that of the 

 corresponding portion of the basilar, and further the loss 

 of energy of the wave will be greater for the movements 

 involved being more extensive will involve more internal 

 friction. The smaller waves will hence probably be almost 

 lost before reaching the base, and the larger ones will, 

 apparently, die out at the base in the form of small 

 vortices or eddies of the perilymph gradually coming to 

 rest by internal friction of the somewhat viscid perilymph. 

 This is not the place to discuss the far greater effect of 

 viscidity of a fluid in restraining vortical movements than 

 in restraining wave-like movements which involve only a 

 temporary and relatively small internal deformation (or 



