46 ANATOMICAL AND PHYSIOLOGICAL STUDIES ON 



My average value after twenty days is 199 [i; therefore, it 

 is absolutely the smallest in this series of mammals. The rat 

 is also the smallest species examined. 



As shown in the literature quoted, and also in my own results, 

 the membrane increases in its breadth in all the mammals ex- 

 amined from the base toward the apex a relation contrary to 

 that reported by the older authors (Corti, '51, and others). 

 This increase is continuous, but is at first more rapid and after- 

 wards more gradual. The ratios of this increase in the albino 

 rat are given in table 11. 



The next question relates to the breadth of each zone of the 

 membrane according to age. So far as I know, there is no such 

 study in the literature, not even in Retzius. In the albino rat, 

 as shown in table 9, each zone increases in breadth with age. 

 The rate of growth, however, is somewhat different, and in the 

 zona arcuata it is greater than in the zona pectinata (1:1.9 and 

 1 :1.5, respectively), although the absolute value is always greater 

 in the latter. 



As noted above, the membrane increases in its radial breadth 

 from the basal to the apical turn. How, and in which portion 

 of the membrane does this increase arise? Henle ('66) first 

 regarded the breadth of the inner (zona arcuata) as approx- 

 imately constant. 



"Nicht nur in den verschiedenen Regionen einer Schnecke, 

 sondern, soviel ich sehe, selbst in den Sshnecken verscheidener 

 Tiere und des Menschen; sie schwankt nur wenig um 0.01 mm." 

 (Eingeweidelehre des Menschen, 1866, S. 793). 



In the second edition of his book ('73) he states, however, 

 that in the increase of the breadth according to the turn, both 

 zones seem to take part. Hensen ('63) gets in the zona arcuata 

 of the base of the human cochlea the breadth of 19 ^ and in the 

 apex 85 \L. Middendorp ( '68) gives in the cochlea of the cat a 

 continuous increase of the breadth of the zona arcuata from 94 

 to 122.5 {A. ."''"' 



More detailed data are given in table 14. 



According to all these authors, the breadth of both the inner 

 and outer zones increases from base toward apex and results 



