38 IRVING HARDESTY 



turn (the first half of the 2nd turn) of the coil. Develop- 

 ment and differentiation begins in the basal end and precedes 

 toward the apex. Therefore a section through the basal turn 

 would show a more advanced stage of development. 



The tectorial membrane in figure 6 has thickened so that a 

 main body and an axial edge may be easily distinguished. The 

 beginning of the invasion of the axial edge of the greater ridge 

 by the mesenchymal tissue to produce the vestibular lip of 

 the spiral limbus may be seen. Soon the cells of this axial 

 edge, involved in mesenchyme, will cease to produce tectorial 

 membrane, the cessation at the extreme edge having already 

 begun. The outer edge of the body of the membrane is bluntly 

 rounded and coincides with the outer edge of the greater ridge 

 producing it. Attached upon this outer edge of the membrane 

 are the few fibrils produced by the cells of the lesser ridge. 



The amount of the fibrils or fibers produced by the lesser 

 ridge reaches its maximum in pigs between 8 and 14 cm., depend- 

 ing wholly upon the extent to which the elements of the spiral 

 organ have differentiated. The change of character of any of 

 the cells of the ridge into that of any of the various elements 

 of the spiral organ once established, those cells cease to produce 

 the fibrils, become devoted to a different function. From the 

 first they are never more than the outer border of less active 

 cells grading into the non-productive type of the rest of the 

 duct. These fibrils are always more sparse and appear to be 

 supported by a far less amount of the interfibrillar matrix than 

 those of the membrane proper. Further, the amount of the 

 fibrils varies considerably in different individuals in the same 

 stage of development. Figures 6 and 7 (LF) show an amount 

 maybe a little greater than an average in my preparations from 

 pig fetuses. Prentiss must have found a greater amount in 

 the pig than any of my preparations show, especially in his figure 

 6 (pig of 13 cm.), which show^s the product extending well over 

 upon the cells of Claudius and relatively thick, considering that 

 it shows the effect of considerable shrinkage and agglutination. 

 His argument stronglj' urges that a large outer zone of the 

 tectorial membrane is produced by the cells of the spiral organ 



