454 C. W. PRENTISS 



that the membrana is stretched with some tension between the 

 labium and the spiral organ, the tension being greater at the base 

 of the spiral. Whether a membrane of such structure and attach- 

 ments may act as a whole or as a resonator, must be left to 

 physicists to decide. There seems to be little doubt, however, 

 that the membrana tectoria is the structure through which sound 

 waves are transmitted to the auditory cells, and that it is in every 

 way better adapted to this function than the basilar membrane. 

 As it is thin, narrow and perhaps under tension in the basal turns 

 and it has been shown that notes of high pitch are perceived here, 

 it is probable that the membrana of the basal turns responds only 

 to the sound waves of greatest frequency. While the apical turn, 

 which receives notes of low pitch would respond only to waves of 

 low frequency. It does not seem possible that any cuticular 

 chamber could alone respond sympathetically to a given note but 

 rather that a portion of the membrana, of nearly the same breadth 

 and thickness, vibrates as a whole. 



SUMMARY 



1. The membrana arises as a thin cuticular plate which is first 

 developed over the free ends of the columnar cells which form the 

 greater (inner) epithelial thickening of the basal cochlear wall. 



2. As it is present in fetuses of 5 cm., before the development 

 of the hair cells in the spiral organ, it cannot be regarded as 

 developed from these hairs. 



3. The greater epithelial thickening gives rise to the epithelium 

 of the labium vestibulare, to the lining of the spiral sulcus and 

 to the inner half of the spiral organ (inner supporting cells, and 

 probably to the inner hair cells and inner pillars). The lesser epi- 

 thelial thickening forms the external portion of the spiral organ. 



4. The membrana grows in thickness by the secretion of a 

 cuticulum formed between the ends of the epithelial cells, rapidly 

 at first over the cells of the greater epithelial thickening (5 to 

 13 cm. stages), later over the cells of the lesser epithehal thick- 

 ening. 



