46 IRVING HARDESTY 



of it: (1) Each of the pillars of the organ appears to be produced 

 b,y a separate cell which is entirelj^ used up in the process and its 

 nucleus disappears; (2) the 'foot cells/ one bracing against the 

 inner side of the basal end of each pillar, seem to be derived 

 separately, and though they may aid in nourishing the pillars, 

 they probably have little or nothing to do with their production. 



Figures 10 and 11 are given to illustrate respectively the 

 actual and the more usually apparent relation of the basal sur- 

 face of the growing tectorial membrane to the cells of the greater 

 epithelial ridge producing it. Each of the figures represents a 

 few cells of the outer side of the middle third of the greater ridge, 

 figure 10 from the 5th half turn of a pig of 15 cm. and figure 11 

 from the 3rd half turn of one of 14 cm. The letter /, indicating 

 the hne of junction between the membrane and cells, is placed 

 on the axial side of each drawing. Figure 10 shows an appear- 

 ance seldom found in the sections of embedded material, but the 

 appearance is, I think, the correct one. By close observation 

 of the specimen from which it was made one may note from 3 to 

 8 fibrils given off from the apical end of each cell. The fibrils 

 pass almost vertically from the surface of the cells and then 

 curve axisward in the part of the membrane previously formed. 

 Each fibril shows a slight, elongated enlargement in its immedi- 

 ate junction with its cell. The number of fibrils observed from 

 each cell probably depends upon the planes in which the cells 

 are split by the section more than upon variation in the sizes 

 of the cells. The cells average about 7 m in diameter. Held 

 computed for the rabbit from 33 to 38 fibrils per each 100 m 

 of the surface line of section of the greater ridge. If 5 fibrils 

 be considered as the average per cell, then each 100 ^ of surface 

 of the ridge in the pig may involve about 70 fibrils. Taking into 

 consideration the third dimension of the cell, as many as 25 

 fibrils may be given off by each cell. 



That, begmning in the apical surface of the membrane, the 

 fibrils course from the axial side outward and then basalward 

 to their cells of origin is due to the fact that the greater ridge 

 increases greatly* in width outwardly while the fibrils are being 

 produced. Later, toward completion of the membrane, as the 



