42 IRVING HARDESTY 



The further increased thickness of the outer edge of the tec- 

 torial membrane, added to it from the basal side, has begun to 

 draw into bundles and tear apart the sparse fibrils. From the 

 preparations of stages below and above that represented by figure 

 8, I think that the cells of the lesser ridge, now the more ad- 

 vanced spiral organ, ceased to produce fibrils in pigs of about 

 12 to 14 cm., and never actively produced them. Being at the 

 beginning involved with those produced by the greater ridge, 

 the fibrils on the lesser ridge and later spiral organ remain con- 

 tinuous with the outer edge of the tectorial membrane proper 

 but they contribute practically nothing to it. When produced 

 in unusually large amount, they may produce the appearance 

 of the loose plexus attached to the freed outer edge of the mem- 

 brane observed by Held in the late fetus, or they may produce 

 the "border plexus of Lowenberg" described in late fetuses by 

 others. But, they partiallj^ if not entirely disintegrate. There 

 is no evidence of them upon the clean, rounded, outer margin 

 of tectorial membrane of the adult pig or even of the pig at full 

 term : they do not show on the fully developed spiral organ, unless 

 they may possibly contribute something to its lamina reticularis. 

 In figure 8, the beginning of the cessation of production and 

 the recession of the cells of the greater ridge is well advanced. 

 The attached axial zone of the membrane ceases earliest to grow, 

 of course. The invasion and growth of the mesenchymal tissue 

 to form the vestibular lip of the spiral limbus soon involves the 

 epithelial cells, which never become so high in the region, pocket- 

 ing them in an inactive condition. Cessation of activitj^ of the 

 cells of the greater ridge proper begins under Huschke's teeth 

 and progresses outward. The activity seems to wane, the last 

 product being less complete than earlier, then the cells begin to 

 recede, their fibrils torn asunder as the space between them and 

 the basal surface of the membrane increases. The receding 

 cells decrease in number. The cells of the outer and thickest 

 part of the greater ridge remain active longest, produce the thick- 

 est part of the membrane and its outer edge. With the recession 

 and reduction of the outer part of the ridge, the membrane has 

 attained its adult proportions. The greater ridge grows pro- 



