36 



two views about this. While a few authors, Kolliker ('67), 

 Hensen ('63), and recently Hardesty ('08, '15), and others hold 

 that only the greater epithelial ridge takes part in the formation 

 of the membrane, most investigators (for example, Bottcher, 

 '69; Retzius, '84; Rickenbacher, '01; Held, '09; Van der Stricht, 

 '18) consider that it originates from both the greater and lesser 

 epithelial ridge. My figure 5, supports the latter view; that is, 

 while the main part is developed from the greater ridge, the 

 outer narrow marginal part is secreted from the lesser ridge. 



The figure in Quain's Anatomy by Schafer ('09) (vol. 3, part 

 2, p. 332, llth ed.,) is from the earlier paper of Hardesty and 

 shows the membrane in the pig as arising from the greater 

 epithelial ridge only. 



Hardesty has corrected this figure in his paper published in 

 1915. Thus in the very early stage after birth in these forms 

 we have three zones, an inner, an outer, and a marginal zone. 

 With age, however, this marginal zone becomes, as Held ('09) 

 and others agree, gradually smaller and smaller, and finally 

 it is difficult to differentiate it from the outer zone. Thus for 

 convenience in measurements I have treated the membrane as 

 consisting of two zones only. 



Comparing the breadth of the inner and outer zones, it is 

 evident that the outer is always the broader. The ratio is 

 (table 4) at birth 1 : 3.78, at three days 1 : 1.43, and then gradually 

 diminishes to 1:1.23 with age. 



Now if we examine the ratios of the total breadth of the 

 membrane according to the turns of the cochlea, we find after 

 six days that the ratio generally increases from base to apex, 

 and that these ratios remain nearly constant after nine days 

 of age, as shown in table 7. 



Thus the ratio between turns I and II is 1:1.1; between turns 

 I and III, 1:1.3; between turns I and IV, 1:1.3. The breadth 

 of the membrane increases, -therefore, in the albino rat gradually 

 from the base to the middle part of the middle turn; from this 

 point it does not increase to the apex. 



Since the breadth at the tip of the apex diminishes greatly, 

 as is generally recognized, Hardesty ('08) found in the pig the 

 following ratios (table 8): 



