THE GENESIS AND STRUCTURE OF THE MEMBRANA TECTORIA 



Erwachsenden als Cylinder zellen erhalten, nur sind sie reihenweise von einander 

 durch die von untcn her emporwachsenden Vorspriinge getrennt worden. " 



Retzius adds that these cells are actually so adherent as to remain attached 

 to the membrana Corti when it is torn away from the underlying tissues and 

 that even after maceration they still remain connected with the membrane ! Such 

 incidents may occur only when the first or second embryonic stage persists. In 

 this respect I am able to state that large areas of the zona papillaris from cats 

 1 to 11 days old are covered by a cubical epithelium free from connective-tissue, 

 while other parts of the same region and the zona dentata show the structure of 

 the adult stage. According to Gottstein (1870) and Waldeyer (1872) half the sur- 

 face of the crista spiralis, next to the attachment of Reissner's membrane, remains 

 covered by a continuous layer of epithelial cells. Of course, such elements may 

 become detached by maceration or by stripping off the membrana tectoria. 



DEVELOPMENT OF THE MEMBRANA TECTORIA. 

 ON THE SURFACE OF THE GREATER EPITHELIAL RIDGE. 



The process of genesis of the membrana tectoria is conspicuous mainly at the 

 most active portion of its anatomical substratum that is to say, at the surface 

 of the greater epithelial thickening. Tangential sections must be obtained, since 

 they exhibit the best figures, as demonstrated by figures 25 and 26. One observes 

 the superficial mosaic (my) removed by the razor from small areas (mf) , where the 

 recently formed part of the membrana tectoria is visible. At ml' exists a kind 

 of pale mosaic of another nature, reproducing that of the subjacent anatomical 

 substratum. The terminal bars are replaced by larger dense lines and the 

 apices of the cells by paler, more circular areas. The lines exactly overlie the 

 system of terminal bars which is cut off, and their substance is not only in close 

 contact with the bars, but is in continuity with them at the periphery of the 

 small islands. The pale, more fluid substances in the mazes of this network overlie 

 the polygons of the mosaic, the cytoplasmic apices of the epithelial cells, and are 

 also in continuity with them. Hence the compact lines must be considered as 

 produced by the bars and the content of the mazes by the superficial cytoplasm. 



By Mallory's method the lines are stained blue, the bars red; by the use of iron 

 hematoxylin and Congo red the former are rosy, the latter dark blue; after iron 

 hematoxylin and light green the first are intensely green and the second dark bluish. 

 ( !onsequently, the chemical composition of the line must be regarded as different 

 from that of their generating substratum. 



The cochlea of a pig embryo of 93.5 mm. fixed by the uranium nitrate method 

 of Ramon y Cajal shows in some places (fig. 27) the terminal bars (tb) and the dense 

 part (///) of the superficial membrana tectoria stained black. The compact lines 

 dl>') are thinner than the bars and situated in a different plane; hence they are not 

 quite in focus. The result of this treatment affords another striking proof of the 

 real origin of the lines and of a chemical composition more or less similar to that of 

 t lie liars. The lines (tut 1 , figs. 25 and 26) are larger than the bars and at first sight 



