142 Irving Hardesty 



cells of the organ of Corti to the edge of the labmm vestibulare. The 

 exhaustion begins along the inner side of the greater epithelial thicken- 

 ing, at the edge of the labium vestibulare and gradually proceeds out- 

 ward. Thus the first portion of the tectorial membrane to become free 

 from its parent epithelium, that is, to cease growing, is the strip adja- 

 cent to the labium vestibulare. Sections from pigs of 15 and 17 cm. 

 usually show a beginning recession of the epithelium in this region, 

 and it is probably indicated in Fig. 10. (More strictly speaking, the 

 portion of the membrane which first ceases to increase in thickness is, 

 as mentioned above, the inner zone, attached upon the surface of the 

 labium vestibulare.) The exhaustion of the epithelial thickening gradu- 

 ally passes outward till the last region of it that is active and attached 

 to the tectorial membrane is its outer edge, or the region adjacent to 

 the organ of Corti, which region, in the previous growth changes as 

 noted above, became its thickest region. Finally this region recedes, 

 the remains of the cells liquefy and the tectorial membrane is left 

 entirely free from the cells which give rise to it. Transverse sections 

 of the cochlear duct of pigs from 20 to 25 cm. often show a mass of dis- 

 integrating epithelial cells lying against the inner supporting cells of the 

 organ of Corti, which mass represents the vestige of the greater 

 epithelial thickening. 



By the above processes of increase, recession and disintegration, the 

 disposition of the fibers within and in the under surface of the tectorial 

 membrane may be explained as well as the position which the membrane 

 finally attains with reference to the organ of Corti (the lesser epithelial 

 thickening). 



The retrogi-ession of the epithelial cells undoubtedly results in a 

 decrease in the width of the space occupied by the greater thickening 

 (the space which becomes the floor of the spiral sulcus), and this 

 decrease results in the inward displacement of the organ of Corti to 

 its final position under the outer zone of the tectorial membrane. 

 Counts of the cells comprising the greater epithelial thickening in the 

 third half- turn of several cochleae from pigs of 14 to 15 cm. gave an 

 average of 93 cells per transverse section. Counts of the cells lining 

 the spiral sulcus, up to the inner supporting cells of the organ, in the 

 same region of several fully developed cochlege gave an average of only 

 21 cells, the averages showing that the space in the fcetal cochlea 

 contains four times as many cells as the developed. Measurements of 

 the width of the floor of the spiral sulcus of the developed cochlea gave 



