122 ANATOMICAL AND PHYSIOLOGICAL STUDIES ON 



The greater epithelial ridge has already disappeared in large 

 part and been replaced by a furrow. Pressure displacement 

 of tissue in the direction of the least resistance is common in 

 organogenesis. Thus the inner pillar cell is subject to pressure 

 by the rapid growth of the outward lying and greater part of 

 the papilla spiralis and moves in the direction of the least resis- 

 tance, therefore inward; the head most and the base not at all. 

 As shown in table 44, the rapid decrease in the radial distance 

 between the labium vestibulare and the head of the inner pillar 

 cell is very evident. The arch of Corti changes its form, now 

 inclining inward, instead of outward as heretofore. The lamina 

 reticularis runs not parallel to the basilar membrane, but ascends 

 outward. The tunnel of Corti also changes more or less its form. 

 Nuel 's space now appears possibly as a result of this displacement 

 of the papilla spiralis. Thus we see a change in the position 

 of the sense organ with reference to the membrana tectoria. 



With the inward shifting of the papilla, the hair cells come 

 under the basal surface of the membrana tectoria. It is probable 

 that the increase of the relative length of the membrane also 

 takes part in this, since the increase in the breadth of the inner 

 zone of the membrana tectoria from one to twelve days is as 

 1:3.4 (table 4), while the increase in the breadth of the basilar 

 membrane is as 1:0.5 during the same interval (table 7). 



Prentiss' ('13) statement that an inward shifting of the papilla 

 spiralis and a consequent displacement of the membrana tectoria 

 does not take place (in the pig) is not applicable to the rat. 



In the rat the labium vestibulare and the inner edge of the 

 head of the inner pillar cell are also two definite points in the 

 same sense, and using them we see an inward shifting of the 

 organ of Corti. I imagine that his observation may have misled 

 him, since the tectorial membrane arises in his preparations 

 from both greater and lesser epithelial ridges, and from the 

 earlier stages covers with its outer part the papilla spiralis. 

 Thus the shifting of the organ inward does not necessitate a 

 change in the position of the papilla with reference to the mem- 

 brane. In his study of the tectorial membrane in the same 

 animal (pig) , Hardesty ( ' 13) describes a large displacement of the 

 papilla spiralis inward. 



