GROWTH OF THE INNER EAR OF ALBINO RAT 121 



I obtained from the measurements given in the tables the 

 following results concerning the position of the papilla spiralis 

 under the basal surface of the tectorial membrane. 



As already stated, since the habenula perforata may be con- 

 sidered after birth as a punctum fixum (Hensen), it is found 

 that the inner pillar cell shifts inward at its inner basal corner 

 during the earlier stage of life. At six days of age it almost 

 always reaches the habenula perforata in the basal turn, though 

 not yet in the apical. At nine days there is no distance between 

 the habenula perforata and the inner corner of the inner pillar 

 cell. 



Gottstein's assumption (no measurements) that the labium 

 tympanicum grows outward and approaches to the arch of Corti 

 is not applicable to the rat, as shown by my tables. 



The outer pillar cell also moves outward in all the turns 

 through life, but only slightly after nine days. This result does 

 not agree with that of Hensen ('63), who found in the ox the 

 outer pillar cell to move inward a little at the base, not at all 

 in the middle turn and outward at the apex. Bottcher 's outward 

 movement of the outer pillar cell at the hamulus in the cat is 

 90 [x and much larger than in the rat. 



Contrary to Hensen, Retzius ('84) also finds in the rabbit an 

 outward movement of the base of the outer pillar cell throughout 

 all the turns. On the other hand, during the earlier stages of 

 development, the top of the arch of Corti moves outward from 

 the labium vestibulare through the outward pressure of the 

 greater epithelial ridge. At this stage the main part of the 

 membrana tectoria does not yet reach to the sense cells, though 

 the part produced from the lesser epithelial ridge spans the 

 spiral organ and connects with the outer part of the papilla. 



After nine days of age the condition of the organ is quite 

 different. The most remarkable anatomical changes from the 

 earlier condition are the rapid increase in the length of the outer 

 pillar cells, in the height of the pillar cells above the basilar 

 membrane, in the height of the papilla spiralis at the third series 

 of the outer hair cells, in the height of Deiters ' cells, and in the 

 height of Hensen 's supporting cells. Also the tunnel of Corti 

 appears. 



