220 PHYSIOLOGY CHAP. 



Kishi further points out that if the basilar membrane is to 

 excite the hair-cells by its movements, these should be vertical, 

 not oblique to its plane. Moreover, the inner hair-cells do not lie 

 above the basilar membrane, but are placed above the habenula 

 perforata, so that they cannot be effectively influenced by the 

 movements of the membrane. On the other hand, it is easy to see 

 how movement of the stapes can produce gentle oscillations of the 

 tectorial membrane sufficient to excite the filaments of both inner 

 and outer hair-cells. Like the basilar membrane, the free or 

 outer zone of the tectorial membrane is fibrous in structure, and 

 increases in size from the base to the apex of the cochlea. Lastly, 

 Kishi states that in the first turn of the cochlea the mernbrana 

 tectoria is not only less wide, but is tightly stretched, while in the 

 apical turn, where it is more than three times as wide, it is loosely 

 stretched. So that from no point of view can it be an advantage 

 to regard the basilar, instead of the tectorial, membrane as the 

 vibrating organ capable of transforming the physical sound-waves 

 into physiological auditory impulses. 



On considering the mode of propagation of the sound-waves 

 to the internal ear we find an additional argument in favour of 

 the view that the tectorial rather than the basilar membrane is 

 the vibrating part of the cochlea. 



We followed the sound-waves through the tympanic apparatus 

 as far as the membrane of the fenestra ovalis, which moves trans- 

 versely by means of the plate of the stapes, its range not exceeding 

 0'04 mm., and throws the perilymph into motion. This, if driven 

 inward, must necessarily exert pressure outwards at some other 

 part of the organ, because fluid is incompressible. Obviously 

 the membrane of the fenestra rotunda may fulfil this object, and 

 many physiologists consider it to be a counter-aperture, moving in 

 the opposite direction to the fenestra ovalis (Mach and Kessel). 

 Some have imagined that owing to the impulses from the stapes 

 the fluid of the labyrinth is driven along the scala vestibuli and 

 through the helicotrema to reach the membrane of the fenestra 

 rotunda. But the fallacy of this view is obvious, not only from 

 the fact that owing to the rapidity at which the sonorous 

 vibrations succeed one another there is not time for the wave- 

 movement of the labyrinthine fluid to follow this long course 

 but also from Pascal's law, according to which pressures exerted 

 in a cavity with rigid walls, closed at one point by a membrane, 

 are transmitted uniformly to all parts of the internal wall. It 

 must be assumed that the sound-waves, on reaching the fluid of 

 the labyrinth, follow no particular course, but are transmitted 

 simultaneously in all directions, through the two scalae of the 

 cochlea. But the waves of impact ascending by the scala tympani 

 can only be transmitted to the endolymph with difficulty, either 

 because they are at least partially damped by the yielding of 



