GROWTH OF THE INNER EAR OF ALBINO RAT 123 



According to him, the shifting of the organ consists of, 1, the 

 moving axisward of the organ itself, and this constitutes the 

 main shift; 2, the upgrowth of the outer supporting cells, and 

 this contributes a small part to the shift, and, 3, a slight increase 

 of the vestibular lip of the spiral limbus which may contribute 

 a still smaller part. The relation in the rat, however, is different. 

 The moving inward of the papilla itself is not seen in the rat. 

 In the earlier stages the inner basal corner of the inner pillar 

 cell alone shifts inward and reaches the habenula perforata. 

 On the other hand, the outer pillar cell moves outward and 

 the head of the inner pillar cell also, at earlier stages, towards 

 the cells of Hensen. Therefore, during the earlier stages the 

 arch of Corti moves rather outward, owing to the pressure of 

 the growth of the greater epithelial ridge. Since the habenula 

 perforata is to be regarded as a fixed point, the inward displace- 

 ment of the head of the arch of Corti and of the papilla spiralis 

 is not due to the active shifting inward of the organ itself, as 

 Hardesty ('15) thinks, but to the disappearance of the greater 

 ridge and the passive pressure exerted by the upgrowth of the 

 outer pillar cells and Deiters' and Hensen 's cells. The vestibular 

 lip of the spiral lamina and the tectorial membrane itself both 

 increase in their length a little, and these increases play some 

 part in the change of the position of the papilla spiralis with 

 reference to the basal surface of the tectorial membrane. 



The membrana basilaris is not concerned with the moving 

 inward of the organ. It increases its length with age in all the 

 turns, but we do not find the change in the position of the feet 

 of the pillar cells on the membrane in such a sense that the 

 feet move inward on it. 



Thus the shifting of the papilla spiralis inward in the rat 

 during the development takes place rather in the manner de- 

 scribed by Retzius. 



Hardesty ('15) states that in the apical turn of the cochlea the 

 organ may be moved axisward a distance equal to about half 

 the maximum width of the greater epithelial ridge, the maximum 

 width of the ridge representing approximately the width of the 

 outspanning zone of the membrane produced upon it. 



