GROWTH OF THE INNER EAR OF ALfcINO RAT 



93 



TABLE 66 



Lengths of inner and outer pillars in several mammals according to different authors. 



Measurements in n 



16. Inner and outer hair cells. For a long time the inner 

 and the outer hair cells have been regarded as the most important 

 elements in the papilla spiralis. As these sense cells have a 

 delicate histological structure which is readily altered, the 

 systematic study of their growth, especially after the appearance 

 of hearing, is a difficult matter. Though there are some observations 

 on the length of these cells, detailed studies on their growth 

 have not been made heretofore. I have therefore endeavored 

 to follow the changes of their size during the postnatal period. 

 It is first necessary to determine the form of these cells. They 

 are generally described as cylindrical, but this description is 

 inexact. Moreover, the inner and outer hair cells are somewhat 

 different in shape. The former has on the surface a large oval 

 terminal disk, which is wide hi the spiral and narrow in the 

 radial direction. This narrows downwards to a thinner neck 

 which expands into the broader body and terminates in a more 

 or less round but somewhat pointed irregular end. 



