DEVELOPMENT OF THE MEMBRANA TECTORIA 451 



braiia is composed of chambers, filled with fluid and open at their 

 lower ends, while over the spiral organ these ends are assumed to 

 be closed by the ends of the epithelial cells. The action of most 

 fixing reagents and alcohol is to take water from the membrana. 

 This would cause the open chambers to shrink, narrow, and so 

 suddenly diminish the width and length of the membrana.- As 

 the membrana has the form of a spiral the shrinkage of the outer 

 portion of the membrana throughout its whole length would tend to 

 draw it toward the labium and away from the spiral organ, as it would 

 diminish the diameter of the spiral. The effect would be most 

 marked in the larger basal turns and it is there that the mem- 

 brana is almost invariably torn away from the spiral organ even 

 in late fetal stages. This alone would account for the detach- 

 ment of the membrana from the spiral organ in most fixed prepa- 

 rations. Over the spiral organ, assuming that the membrana is 

 attached, the chambers would be closed by the ends of the epithe- 

 lial cells. Upon the action of fixing reagents or alcohol, the with- 

 drawal of water must take place chiefly about the ends of the 

 chambers as their cuticular walls are not permeable. The result 

 would be the shrinkage of the chambers and their separation from 

 the cells. Even after the membrana is freed from its attachments 

 Hardesty has shown that it shrinks very badly during the process 

 of dehydration and clearing, and I have noted the same. The 

 shrinkage of the membrana may also be aided by.normal tension 

 in pulling the membrane away from the spiral organ. It is very 

 possible that such tension exists especially in the lower turns of 

 the cochlea, as held by Kishi ('07). 



THE FUNCTION OF THE MEMBRANA TECTORIA 



It is not my intention here to go into a detailed account of the 

 physiology of audition but simply to emphasize certain anatomi- 

 cal facts which have a bearing upon the transmission of the sound 

 waves. Recent investigators all agree that the hair cells form the 

 perceptive end organ of the cochlea and that the tectorial mem- 

 brane is probably the medium through which the sound waves are 

 transmitted to the hairs of the auditory cells. Arguments against 



