ACTION OF THE TECTORIAL MEMBRANE 505 



offered by the walls of the very small canals of the cochlea and 

 the structures contamed withm them. 



As noted above, the size and volume of the tectorial membrane 

 so increases in passing from the basal to the apical end that the 

 volume or load carried by a given short length of the apical end 

 is about 40 times that carried by the same length of the basal 

 end. This increase seems to occur uniformly throughout, or 

 perhaps a little less rapidly through the basal turn of the coil. 

 It is noted that these variations in the proportions of the tec- 

 torial membrane are far greater than can be claimed for any 

 other structures of the cochlea, especially the basilar membrane. 

 Increase of volume or the load carried by a structure means 

 increase of its inertia. The much thinner and narrower basal 

 end of the tectorial membrane extends in the region of the fen- 

 estra vestibuli (ovalis) , or the region at which the vibrations are 

 imparted to the endolymph by the basis of the stapes. Obvi- 

 ously, a thin, narrow strip offers less resistance to agitation than 

 a thicker, broader strip of the same material. Thus, the thin, 

 narrow basal end of the outspanning or vibratory zone of the 

 tectorial membrane may be thrown into vibration by notes of 

 such high vibration frequencies as would be wholly damped out 

 in overcoming the inertia alone of a more voluminous portion 

 of the membrane. The volimie of the outspanning zone of the 

 membrane increases with its distance away from the basis of the 

 stapes and, therefore, among the appreciable sounds of higher 

 vibration frequencies, those of different frequencies must be 

 capable of throwing into vibration different lengths of the mem- 

 brane, beginning at its basal end. The resistance offered by the 

 endolymph and walls of the labyrinth, as well as the inertia of 

 the membrane itself, contribute to their being damped out at 

 their respective distances toward the apex of the cochlea. Since 

 vibrations of higher frequency are damped out more quickly 

 in transmission through a medium, there may be sounds whose 

 vibration frequencies as imparted to the endolymph are such 

 that they agitate the basal end of the membrane alone sufficiently 

 for the required impingement against the hairs of the hair cells. 

 And, of course, there must be vibration frequencies of similar 



