GROWTH OF THE INNER EAR OF ALBINO RAT 39 



By using this vital-fixation method we get perfect sections which 

 can be used to solve the problem of the shifting of the organ 

 of Corti — an event which I will discuss later. 



2. Membrana basilaris. The membrana basilaris of the 

 cochlea stretches between the limbus laminae spiralis and the 

 ligamentum spirale. The acoustic terminal apparatus is situated 

 on it and according to the dominant Helmholtz-Hensen theory, 

 this membrane is to be considered as very important in tone 

 perception. The row of the fine holes, foramina nervina, 

 is generally designated as the inner boundary of this membrane. 

 Strictly speaking, however, the beginning of the membrane is 

 at the outer edge of the labium tympanicum, which sharpens at 

 first beyond the foramina nervina and passes over to the sub- 

 stance of the membrana basilaris. Practically it is almost 

 impossible to decide exactly the point of transition. Thus I 

 have used in the measurement of the membrane the foramina 

 of the habenula perforata as an inner limiting line following in 

 this Retzius, ('84) Schwalbe ('87), and others. Here it is to be 

 mentioned that the organ of Corti lies with its inner portion 

 not only upon the inner part of the membrane, but extends to 

 the foramina nervina also. 



The membrana basilaris is usually divided into two portions; 

 the inner, termed the zona arcuata, and the outer, the zona 

 pectinata. The former stretches from the habenula perforata 

 across the base of the tunnel of Corti to the outer edge of the 

 foot of the outer rods of Corti ; the latter extends from this point 

 to the ligamentum spirale (fig. 2), 5 = inner zone, 10 = outer zone. 



In table 9 (chart 7) are given the values for the total radial 

 breadth of the membrane, that of each zone, and the ratios 

 between them. At the bottom of each column are given the 

 ratios at 1 to 546, 12 to 546, and 20 to 546 days of age. In the 

 total radial breadth of the membrane, as the table shows, there 

 are large differences on age from birth to nine days. Between 

 1 day and three days the increase is 30 [i and between three days 

 and six days, 28 [x. After nine days the breadth increases more 

 slowly but continuously to old age. 



