DEVELOPMENT OF THE MEMBRANA TECTORIA 



433 



greater cell thickening show not so many layers as in the pre- 

 vious stage but the cells are longer than the pillar cells of the 

 spiral organ. Near the inner angle of the cochlear duct the 

 membrana tectoria has increased very Uttle in thickness and still 

 forms a thin cuticular layer over the epithelial cells. Externally 

 the membrana now extends beyond the outer hair cells of the 

 spiral organ at which point a thin cuticle is just being formed. 

 Over the spiral sulcus the growth of the membrana has been 

 most rapid and here it is thickest. It appears to be composed 



Fig. 3 Section through the second spiral of the cochlear duct from a fetus 

 8.5 cm. long, showing the basal half of the cochlear duct and a portion of the scala 

 tympani; h.c, hair cells of spiral organ; i.ep.c, inner epithelial thickening; o.ep.c, 

 outer epithelial thickening; sc.tymp., scale tympani; other lettering as in figure 2. 

 Oc. 4, Obj. 4, t. 1. 160. 



of numerous parallel fibers or lamellae which are attached to the 

 epithelium between the cells. When traced upwards away from 

 the cells the lamellae converge and curving inwardly are con- 

 tinuous with the thin plate-like inner portion of the membrane 

 which overlies the labium vestibulare. 



The appearance of the tectorial membrane at this stage has 

 been explained correctly, we believe, by Hardesty ('08). After 

 a cuticular layer has been formed as in figure 2, the cells internal 

 to the sulcus spiralis secrete very slowly or cease altogether. The 



