GROWTH OF THE INNER EAR OF ALBINO RAT 151 



above the papilla depends a little bit upon the increase of 

 the length of the membrane itself, but chiefly upon other factors 

 such as the inward shifting of the papilla. The membrana 

 basilaris as a whole shows a small increase o" breadth in the 

 hearing rat. The zona arcuate, however, increases much in 

 its breadth, while the zona pectinata rather decreases. This 

 is due to the development of the pillar cells. The base of the 

 inner and outer pillar cell spread much on the membrane. At 

 the same time the length of the cells, especially of the outer, 

 increases nearly twice as much as in the not-hearing rat. 



Thus the foot of the outer pillar cell moves outward, as Bottcher 

 ('69, '72) stated, while the inner corner of the inner pillar cell 

 does not move in any way, as the habenula perforata stands at 

 a fixed point. This results in a change in the form of the arch 

 of Corti. The hitherto outward inclined arch tends to bend 

 inward and between both inner and outer cells arises a space, 

 the tunnel of Corti. The appearance* of the tunnel seems to have 

 some relation to hearing. The tunnel is always present in the 

 cochleas of hearing rats. Sometimes the tunnel is present in 

 the lower turns, but not in the upper turns in the not-hearing rats. 

 We can say, therefore, that it probably appears through all the 

 turns before the special function of the cochlea begins. In this 

 way the zona arcuata of the membrana basilaris increases its 

 breadth. 



The next striking change is the rapid increase in the size of 

 the Deiters' cells, Hensen's cells, and the resultant change of 

 the form, with an inward shifting, of the papilla spiralis. 



The Deiters' cells increase their height very rapidly; the length 

 of the cell body becomes over twice that in the not-hearing rat, 

 but the processus phalangeus changes only slightly. Hen- 

 sen's cells develop also, but not so much as Deiters' cells. The 

 papilla spiralis thus increases in height. On the other hand, 

 the greater epithelial ridge vanishes inwards from the inner 

 supporting cells and appears as a furrow — the sulcus spiralis 

 internus. Through the pressure of these outward-lying cells 

 the papilla spiralis swings inward as a whole, without really 

 moving on the membrana basilaris. The lamina reticularis 



