62 THE GENESIS AND STRUCTURE OF THE MEMBRANA TECTORIA 



of the organ of Corti are much smaller than the older inner fields (ih, fig. 4). 

 In figure 5 all the apices of the hair-cells are of the same size and the superficial 

 horseshoes (/is), cut from their subjacent cuticular dark plate from which the hairs 

 proceed, are more clearly visible. 



If figures 1, 2, 3, 4, and 5 be carefully compared with one another and with 

 other similar epithelial areas in the cochlea duct, it will be observed that the 

 polygons vary in size. In the first stages of development (figs. 1 and 2) they are 

 largest on the surface of the greater epithelial ridge and much smaller on the future 

 lesser thickening, where their size does not exceed that of the apices of the Hensen 

 cells (mh). But in more advanced stages the fields of the crista spiralis (mcr, fig. 6) 

 and of the Hensen cells become the largest. They do not alter very much on the 

 surface of the greater thickening, although when the organ of Corti is differentiated 

 they extend a little and retain this size more or less until the membrana tectoria 

 becomes detached from its anatomical substratum (fig. 6, ssp). But now they 

 (mg) manifestly decrease along an inner segment (miri) of the greater ridge near 

 the vestibular lip (fig. 6). Figure 24 (N. Van der Stricht) shows this detail much 

 better than my figure 6. 



Figure 4 shows the alterations already mentioned as undergone by the prim- 

 itive small polygons (ml) in figures 1 and 2 when the sensorial (fig. 4) and sup- 

 porting fields appear. During the development of the membrana tectoria they 

 remain more or less unchanged, as may be seen in figure 5; but before reaching 

 the stages of the adult organ of Corti, gradual transformations occur at the apices 

 of the inner and outer pillars and in the terminal bars which form the superficial 

 membrana reticulatis, as described by N. Van der Stricht. To recall details dis- 

 cussed by this author I will give figure 7, which shows the apices of all the constitu- 

 ents of an adult organ of Corti in the bat, in order to demonstrate in connection 

 with the fields of the inner supporting cells a fact of some importance, upon 

 which I shall dwell later, when I speak of the terminal bars. 



Within each area of the indifferent mosaic of the greater ridge exists a central 

 corpuscle (cp), a constituent of the attraction sphere (figs. 1, 2, 4, 6). In reality, 

 on transverse section one sees a diplosome, two granules superposed, of which only 

 one is visible in a tangential section. Generally central, they may become eccen- 

 tric and even reach the periphery of the field. The corpuscle is surrounded by a 

 small, clear area, the medullary zone of the attraction sphere of E. Van Beneden, 

 which is itself encircled by a darker cortical zone (fig. 4) . 



The diplosome also exists in the small fields of the indifferent mosaic cover- 

 ing the future lesser ridge (figs. 1 and 2). When differentiation occurs and is com- 

 pleted the diplosome persists within the sensorial fields, where it becomes periph- 

 eric, occupying the outer or lateral part of the round apex of the hair-cell. It 

 is always surrounded by a small, clear medullary area (cp, fig. 5) beyond the dense, 

 intensively stained circular central plate from which proceed the hairs. This 

 superficial plate is considered by N. Van der Stricht (1908) and Held (1909) as 

 a cuticular product of the cytoplasm. Series of preparations of the cochlea of 

 young cats, fixed by osmic vapors or 1 per cent osmic acid followed by treatment 



