DEVELOPMENT OF THE MEMBRANA TECTORIA 



435 



in the 5.5 cm. stage the membrana tectoria was not yet devel- 

 oped in the upper turn though it had appeared in the second 

 turn. The upper spiral of the 8.5 cm, stage was only slightly 

 .advanced in development beyond that of the basal turn of the 

 previous stage. 



13 cm. stage. The upper coil in this stage showed but little 

 more differentiation of the tectorial membrane than figure 3. 

 In the second spiral, however, a marked difference may be seen 

 (fig. 4). A fibrous basement membrane is stretched beneath the 

 epithelium, extending between the limbus spiralis and the spiral 



Fig. 4 Section through the basal portion of the second turn of the cochlear 

 duct from a 13 cm. fetus; m.bas., membrana basilaris; limb.sp., spiral limbus. X 

 shows point at which later labial teeth appear separating labium from the sulcus; 

 * marks portion of field similar to that shown in figure 5. Oc. 4, Obj . 4, t. 1. 190. 



ligament. The epithelium itself shows a greater thickening in 

 the region of the future sulcus spiralis, the cells being more 

 elongate and clearer. At the axial side they show but one row 

 of nuclei. At X these cells are sharply marked off from the 

 epithelial cells of the labium vestibulare, the latter cells forming 

 the so-called teeth of Huschke. The sulcus spiralis is somewhat 

 deeper than in the preceding stage and the outer supporting 

 cells of the spiral organ are longer and more sharply differen- 

 tiated from the single layer of cubical cells external to them. 

 The membrana tectoria is larger and extends from the inner angle 

 of the cochlea duct to well beyond the spiral organ externally. 



