GROWTH OF THE INNER EAR OF ALBINO RAT 



37 



Comparing these ratios obtained by Hardesty in the pig with 

 mine, there appear to be large differences between them. The 

 reason for these I will discuss later. 



When we consider the breadth in each part of the membrane 

 according to the turn, we find that the increase of the breadth 

 of the membrane in each turn is due to the development of the 

 outer zone. The inner zone, which is adherent to the labium 

 vestibulare, does not increase in the rat as Hardesty ('08/15) 

 found to be the case for the pig, but on the contrary decreases 

 from base to apex — a relation found by Retzius ('84) in the rabbit, 

 cat, and man and confirmed by Rickenbacker ('01) in the guinea- 

 pig. On the contrary, the outer zone increases in breadth from 



TABLE 8 

 Ratios of the breadth of the membrana tectoria according to turn of cochlea (Hardesty) 



base to apex, and in each stage the ratios between the successive 

 turns are nearly the same. These ratios between successive 

 turns, however, show rather large differences according to the 

 different authors. 



My results (table 5) show that the outer zone in the albino rat 

 is nearly two times wider at the apex than at the base. This 

 agrees with what von Ebner ('02) finds in the human cochlea. 



When we consider the thickness of the membrane, we find 

 it thin at birth, but at three days (table 4) it increases rapidly 

 and reaches almost its greatest thickness. This increase in 

 thickness arises through the apposition of new layers to the 

 under surface, as Hasse (73) and others have noted, but very 

 large differences appear between the figures given by various 

 authors. 



