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spirale, consists of two layers, an upper, membrana basilaris 

 propria, and an under, tympanic investing layer (tympanale 

 Belegschicht : Retzius). The former, of course, is divided into 

 two portions, an inner, zona arcuata (Deiters) and an outer, 

 zona pectinata (Todd-Bowman). While the zona arcuata is 

 thin from the beginning of life, the zona pectinata thickens at 

 its central part where it contains cells with oblong nuclei. On 

 passing to the spiral ligament it again becomes thin. In the 

 young, the under layer is not so regular in structure as in the 

 adult. The *cells close to the basilaris propria are arranged 

 vertically. 



On the contrary the cells below them, which vanish in great 

 part with age, have an irregular arrangement; those near the 

 endothelial cells of scala tympani having a more radial arrange- 

 ment. Therefore, this layer is thick, several times the thickness 

 of the basilaris propria, and the thickness increases towards 

 the upper turns. The vas spirale is strikingly large at this stage 

 and lies just under the outer pillar and the Dieters' cells. 



The membrana tectoria, beginning at the inner angle of the 

 ductus cochlearis, where Reissner's membrane rises, covers the 

 epithelium of the limbus laminae spiralis and the greater epithelial 

 ridge, lying close to their surfaces. At the inner part it is thin, 

 but thickens where the greater ridge begins, and at the outer 

 part again becomes thin. In the basal turn there is seen as a very 

 thin strand reaching to Hensen's prominence, but in the apical 

 turn it reaches hardly to the inner hair cell. Although it gives 

 rise to several thread-like processes going to the surface of the 

 papilla, these do not seem to connect with the hairs of the hair 

 cells, but with the terminal plates of the Dieters' cells. 



When we divide the tympanic wall of the ductus cochlearis at 

 the boundary between the greater and lesser epithelial ridges, 

 we observe that the inner portion from the inner angle to the 

 outer end of the greater ridge is far larger than the outer portion, 

 which, however, is the more important for hearing. This 

 relation becomes more evident as we pass from the base to the 

 apex. Moreover, the total radial length of the tympanic wall 



