436 C. W. PRENTISS 



Over the labium vestibulare it forms a thin nearly structureless 

 cuticular layer which becomes thicker and shows lamellae over 

 the labial teeth. In this region it is detached from some of the 

 epithelial cells, a condition due to shrinkage. 



In the region of the future sulcus spiralis and over the inner 

 portion of the spiral organ the membrana tectoria appears com- 

 posed of delicate parallel plates which have the appearance of 

 hairs or fibers in section, and have so been interpreted by some 

 investigators. These plates may often be traced between the 

 cells or about their ends. They are separated by spaces which 

 correspond frequently to the width of the cells at the surface of 

 the epithelium. As one follows the plates away from the epi- 

 thelium the spaces become smaller and the plates or lamellae 

 approach each other until the membrana has the appearance of 

 a solid structure with fine parallel striations; striations which, 

 as we have seen, converge towards the inner angle of the cochlear 

 duct. The relation of the plates or lamellae to the cells lining 

 the future sulcus spiralis is shown in figure 5. Using an oil immer- 

 sion objective the lines were seen as sharply as in a diagram, 

 many passing between the cells and thus taking their origin as 

 an inter-cellular secretion. The thicker lines undoubtedly repre- 

 sent two plates agglutinated. 



Thus far we have shown, conclusively it seems to us, that 

 the membrana tectoria takes its origin partly from cells which 

 in the adult line the spiral sulcus and partly from the inner 

 supporting cells of the spiral organ; and that the cuticular plates 

 are not hke hairs or cilia in their development, as they may 

 be traced between the cells. The next question is whether the 

 outer cells of the spiral organ takes part in the formation of 

 the membrana. Figure 6 shows the relation of the membrana 

 tectoria to the cells of the spiral organ. At this stage the 

 membrana is composed of a thin cuticular plate attached between 

 the ends of the cells by what are apparently delicate threads. 

 Internally (axially) the membrane is thicker and shows converg- 

 ing striae. Externally the membrana extends well beyond the 

 cells of the spiral organ. The hairs of the two outer auditory 

 cells were apparently attached to the outer surface wall of the 



