ACTION OF THE TECTORIAL MEMBRANE 503 



the greater the extent of the basilar membrane involved: that 

 with a faint back-and-forth movement of the stapes only the 

 basal or beginning part of the basilar membrane is set in motion; 

 the greater the back-and-forth movement of the stapes, the 

 further toward the apex of the cochlea will the motion of the 

 basilar membrane extend. This suggestion for the basilar 

 membrane agrees with that offered above as to the behavior of 

 the tectorial membrane, namely, with a note of a given pitch 

 or vibration frequency, a greater amplitude will throw into 

 appreciable vibration a greater extent of the tectorial membrane 

 than a lower amplitude, the extent beginning with the narrower 

 basal end of the membrane and ascending, with the amplitude, 

 along the gradually increasing membrane toward the apex of 

 the cochlea. This action, shown by the model, is one to be 

 expected, since the vibratory motion, imparted at the basal 

 end of the cochlea, necessarily must be gradually absorbed in 

 overcoming the resistance offered by the walls of the cochlea, 

 the inertia of the fluid and the increasing inertia offered by the 

 increasing bulk of the tectorial membrane itself in passing 

 toward the apex of the cochlea. The variations in the diameter 

 of the two sca.lae in passing from base to apex may result in 

 additional decrease in the efficiency of the vibrations imparted. 

 It is suggested that in the functional scale of any auditory 

 apparatus there must be notes sounded whose amplitudes are 

 gradually decreased by the resistance till the vibrations are 

 completely damped out. 



(7) It was further indicated by the model that frequency of 

 vibration or pitch of a sound, considerably more than its ampli- 

 tudes of vibration, determines the extent or length of the tectorial 

 membrane that may be thrown into vibration. The note a 

 (220 vibrations per second) produced with whatever amplitude, 

 would not produce vibrations in the apical end of the tectorial 

 membrane (region 6) sufficient to make and break the current, 

 while it did produce vibrations in region 5. Note b (247 vi- 

 brations per second), the next whole note above a, also produced 

 vibrations in region 5 when sounded with highest amplitude, 

 but none in region 6. Both a and b produced vibrations in regions 



