60 IRVING HARDEST^ 



the adult tectorial membrane, though their few fibers may re- 

 main attached to its outer edge till torn asunder in the later proc- 

 esses. The membrane is produced by the greater ridge. 



11. With the differentiation of the spiral organ from the lesser 

 epithelial ridge, the organ begins to increase in thickness and, 

 though most of this increase occurs in the stages before full 

 term, some of it seems to occur after birth. Growth changes 

 of the organ occur least in the basal end of the cochlea. It is 

 suggested that at least four cells of the lesser ridge take part 

 in a given section in forming the elements comprising the walls 

 of the spiral tunnel. 



12. The outermost part of the greater epithehal ridge becomes 

 thicker by growth pressure than the remainder, is active for a 

 longer period, produces the thicker part and outer edge of the 

 tectorial membrane, and its outermost cells, in the process of 

 recession and disintegration of the ridge, seem to differentiate 

 into the inner supporting cells of the spiral organ. 



13. In the production of the tectorial membrane, each cell 

 of the greater epithehal ridge may contribute an average of 25 

 fibrils to the membrane. Each fibril seems to show a slightly 

 elongated enlargement at its junction with its cell. In the region 

 of the immediate surface of the ridge, that of the product of the 

 most recent activity of the cells, the interfibrillar matrix does 

 not appear as abundant, or so completely produced, as in the 

 older body of the membrane. This less completely formed 

 part of the membrane shows shrinkage effects of the reagents 

 in all sections of the cochlea. 



14. With the growth in width of the greater epithelial ridge 

 in the early stages, the differentiating spiral organ (lesser ridge) 

 situated along the outer edge of the growing tectorial mem- 

 brane, is carried outward. The developed spiral organ acquires 

 its position well under the basal surface of the tectorial mem- 

 brane almost entirely by being carried axisward during the com- 

 pletion of the membrane. As the cells of the greater ridge re- 

 cede from the membrane they disintegrate to about one-twenty- 

 fifth of their greatest number, thus more than relieving all growth 

 pressure on the axial side of the spiral organ. During this proc- 



