68 THE GENESIS AND STRUCTURE OF THE MEMBRANA TECTORIA 



teeth (t) and representing the superficial mosaic, which is never invaded or traversed 

 by the proliferating connective-tissue. The transverse diameter of some cell-bodies 

 is the same at various heights, but in others it is slightly reduced and constricted 

 near the surface. 



Between the dark epithelial elements exists a clearer collagenous mass (/,), 

 deeply stained by aniline blue, within which arc noticed darker filaments stained 

 red. These are the prolongations of subjacent connective-tissue cells (pr). These 

 connective interepithelial teeth of Huschke extend bodily into the depth (st) and 

 are largely in continuity with the subepithelial substratum. Many preparations 

 show this detail more distinctly. 



Tangential sections at this stage are very interesting (figs. 17, 18, 19). Figure 

 17 shows a portion of the third turn of the cochlea in a new-born dog. Above 

 one sees the superficial epithelial mosaic (mcr) like a veil formed by elongated poly- 

 gons, the apices of the epithelial cells, which are separated by darker lines, thin 

 terminal bars stained blue by iron hematoxylin. The long axis of these fields is 

 perpendicular to the axis of the rather dense subjacent bands (pb) which represent 

 cytoplasmic epithelial zones deprived of their nuclei because the razor has taken 

 only the superficial segments of the cells. In the lower part of the figure the veil 

 disappears and one notices nuclear bands (nb) , the section of the deeper segment 

 of the epithelial elements. These bands are more or less parallel in the zona den- 

 tata (zd), ramified and anastomosed in the form of a network in the zona papillaris 

 (zp). Figure 19 shows much better the reticulum of nuclear bands (nb) in a pig 

 embryo of 127 mm. The zona dentata is cut more superficially and one sees its 

 mosaic (mcr) and a part of the membrana tectoria (ml'). Figures 17, 15, and 18 

 demonstrate also that the neighboring epithelial cells of the greater ridge (essp), 

 conspicuous by their larger and darker nucleus, join the epithelial elements of the 

 crista spiralis in the formation of the cell-bands. The connective tissue between 

 the nuclear bands represents the teeth of Huschke and consists of a clear colla- 

 genous mass and darker granules (pr) , the transverse section of the prolongations 

 of subjacent connective cells. 



In areas of figure 17 and more clearly in figure 18 one sees other details. A 

 system of regular parallel filaments crosses the teeth (t) transversely like inter- 

 cellular bridges and connects two neighboring nuclear rows (nb). There seem to 

 exist as many bridges as there are nuclei in one column. Preparations of pig embryos 

 of 127 and 137 mm. display similar bridges and their regularity proves that they 

 represent real structures. I think that they are thin cytoplasmic membranes 

 persisting between the, cells of two neighboring rows after their separation by the 

 proliferating connective tissue. At this third stage of its development the sub- 

 epithelial parts of the teeth of Huschke are marked on tangential sections by large, 

 thick, dense, parallel, collagenous bundles, within which many cell prolongations 

 are embedded. 



4. The final or adult stage is characterized by the fact that the cytoplasmic 

 epithelial sheets are very thin and constricted in their superficial non-nuclear seg- 

 ment, which is in continuity with the persistently intact superficial mosaic; they 

 are much larger at the level of their deep nuclear segment. 



