\\\T..\II. \L AND PHYSIOLOGICAL STUDIES ON 



triangle and Btands upright on the basilar membrane. Tn the 



apical turn the inner pillar cell is not yet so long as in the lower, 

 turn- ami is still inclined outwards. The head plates and pillars 

 are fairly prominent, bul there is as yet no space between them. 



The outer hair cells have grown and are inclined inward. 

 Deiters' and Hensen's cells have not yet begun to develop, as 

 have the other elements of the organ of Corti just described. 



In the membrana basilaris we see the reduction of cells in 

 the tympanic covering layer. The vas spirale shows more or 

 less reduction. The membrana tectoria increases its radial breadth 

 following the associated structures. The so-called marginal zone 

 connects with Hensen's cells and the lamina reticularis by 

 fibrous processes. 



Among live nine-day-old rats, as shown later, one responded 

 tn the tests for hearing. As the majority of them gave no re- 

 action, the cochlea of the latter, non-hearing rat, may be taken 

 a- the type for this age. The differences between the cochlea 

 of the hearing and non-hearing rats will be mentioned later. 



In rats of this age (fig. 7.) the cochlea is still further advanced. 

 The sulcus spiralis internus appears through all the coils, and is 

 deepest and broadest in the basal turn, diminishing in depth 

 "i- gradually toward the apex. The cells covering the space are 

 low and cuboid iu the lower turns, but in the apical turn they are 

 yet relatively high, cylindrical cells. 



These cells probably have their origin from the long slender 

 cells of the greater epithelial ridge, as Bottcher ('69) and others 

 maintain, although Cottstein (72) and some others think that 

 they come by the outward migration of the epithelium of the 

 limbus spiralis, and Retzius ('84) regards this latter view as the 

 more probable. 



The inner and outer hair cells become large and approach 

 th.-u- mature form. The supporting cells of the inner hair cell 

 are very evident. 



The pillar cells develop more and more, their radial breadth 



incr< and the pillar- and headplates also become distinct. 



we see a small space between the inner and outer 



pillar cells in the lower turn, but not in the upper. Nuel's space 



