The Nature of the Tectorial Membrane 1T3 



(3) The scala tympani increases in diameter in passing from the 

 helicotrema to the fenestra cochlese (rotunda) . Therefore, supposing that 

 the sound waves passing in the scala vestibuli return without interfer- 

 ence in the scala tympani, they would not only be fainter because of the 

 resistance of the endolymph and walls of canal through which they have 

 passed, but their amplitude would be further decreased because of their 

 being dispersed over the increasing space of the scali tympani. So, 

 Hensen's idea must assume that the stimulating resonant action of the 

 basilar membrane is accomplished with waves of less amplitude than 

 when entering the cochlea. 



(4) Anatomical studies of the basilar membrane suggest that it is 

 wholly incapable of moving as sensitively as the tectorial membrane to 

 waves in the scala vestibuli. Not only is the basilar membrane firmly 

 continuous along its either edge with the walls of the labyrinth and 

 invested above and below by layers of other tissue, but even when torn 

 away as a free strip, it is far more stiff than the tectorial membrane. 

 When teased free in fresh preparations it is rigid enough to more than 

 retain its shape, and its flexibility, compared with that of the tectorial 

 membrane, is as a wooden board compared with a strip of tissue paper. 

 It must at least resist wave motion in the endolymph far more than the 

 tectorial membrane Avhich lies suspended in the endolymph, one edge 

 free, and by position is the first to receive the impact of the waves. 



To these objections to Hensen's idea may be added the ol3Jections 

 enumerated on another page against the idea that the basilar membrane 

 is a resonance mechanism at all. 



From the anatomical standpoint, the basilar membrane may be con- 

 sidered as nothing more than a thin, fiat tendon, thicker along its edges, 

 whose purpose is to so strengthen the fioor of the cochlear duct that it 

 may firmly support the organ of Corti and at the same time be thin 

 enough to allow the presence and necessary caliber of the scala tympani 

 below it. 



The vestibular (Eeissner's) membrane is considered as having little 

 to do with the function of the organ of Corti. By development, it is the 

 remains of the outer wall of the embryonic cochlear canal, after the 

 liquefactions of the mesenchymal tissue resulting in the scala vestibuli. 

 It may serve as a protection to the organ below, damping violent agita- 

 tions in the scala vestibuli and preventing upward displacement of the 

 tectorial membrane. It is weakest along its edges, which condition 

 gives, in teased cochlea, somewhat the impression of its being hinged to 



