A NEW THEOEY OF HE AKIN G-. 327 



be spoken of as forwards or backwards according as it is 

 towards the apical or towards the basal region. 



First as to the upper membrane. The fenestra ovalis 

 is placed at the junction of vestibule and cochlea. 

 Pressure applied to it affects the fluids within and around 

 the membranous vestibule equally, as also around and 

 within the canalis reuniens. Any movement of the upper 

 membrane near the junction of the walls of the canalis 

 reuniens with it will therefore be due to friction only and 

 not to difference of pressure on its two surfaces. This 

 portion of the upper membrane is moreover loose and 

 flabby and the movements which can only be slight will 

 involve no stretching. The membrane is moreover light, 

 broad, thin, soft and relatively inelastic (on account of its 

 looseness at this point) and it will move therefore freely 

 as part and parcel of the fluids in which it is immersed, 

 such elasticity as it possesses not being brought into play. 

 The effects of a wave of this membrane if one should be 

 produced would be identical with, but enormously smaller 

 than, the basilar wave to be considered directly. For the 

 present therefore we may without error ignore the 

 existence of the upper or Keissnerian membrane, and look 

 upon the basal portion of the cochlea as consisting of only 

 two chambers or canals separated from each other by the 

 basilar or lower membrane. 



The lower membrane is very different. It is exceedingly 

 narrow, its basal end may be said to end almost in a 

 point : it is not only exceedingly stiff by virtue of its 

 transverse fibres, but its elasticity is enhanced by the 

 transverse tension under which it is stretched between 

 the two bony ridges supporting it. A very slight dis- 

 placement will therefore instantly call its elasticity into 

 play, and the movement towards the lower canal affecting 

 first its most basal portion will rapidly extend along the 



