GROWTH OF THE INNER EAR OF ALBINO RAT 



33 



The values at birth are relatively greater than those at three 

 days, as noted above, due to the undevelopment of the labium 

 vestibulare. The inner zone grows in a like manner in breadth, 

 but not so rapidly as the outer zone, and hence its relative breadth 

 diminishes gradually from base to apex. 



Table 6 shows these relations. While the ratios in the inner 

 zone decreases from base to apex, those in the outer zone increase. 

 Thus the ratios in the inner and outer zones according to the 

 turns go in opposite directions. As stated above, the radial 

 breadth is generally larger in the outer zone, but this relation 

 is, in general, reversed in turn I, table 5. 



TABLE 6 — Condensed 

 Ratios of the radial breadth of each zone of the membrana tectoria 



In turn I the average ratios are, after eight days, smaller than 

 1.0; therefore, the inner zone is wider than the outer in turn I. 

 It increases in all ages from turn II toward the apex. 



In table 7 are given the ratios between each turn of the cochlea. 

 The ratios after nine days of age are practically constant according 

 to age, but those between turns I and II are always smaller 

 than the others; the ratios for the two latter being alike. The 

 ratio at one day is, however, an exception, as stated already. 



As the measurements show, the membrana tectoria is at birth 

 relatively undeveloped; it is thin and immature. After birth 

 it increases rapidly during the first nine days, a statement which 

 applies generally to the postnatal growth of the organs of the 

 albino rat. Thus we get a ratio of the radial breadth 1 :1.7 between 

 1 and 546 days, but after twelve days the ratios remain prac- 

 tically 1:1.0. (Table 4.) 



