PROPORTIONS OF THE TECTORIAL MEMBRANE 41 



greater ridge throughout. Its outer third cups around or 

 clasps the more elevated outer third of the greater ridge, and 

 its rounded edge is curved basalward to terminate at the inner 

 hair cells of the young spiral organ (figs. 7 and 8). The cells 

 comprising the outer margin of the greater ridge are directed 

 outward, diverging toward a direction parallel with the sur- 

 face of the spiral organ and thus maintaining the position approxi- 

 mately vertical to the basal surface of the enclasping outer edge 

 of the membrane. The bluntly rounded outer edge of the 

 membrane is frequently torn loose in the preparation of the 

 sections. Then it may be straightened outward over the spiral 

 organ, either projecting free from it or often pressed down upon 

 it when distorted. Quite often, when torn free or distorted 

 by pressure, the edge appears shrunken to a flattened, dark 

 staining projection. Even when undisturbed and undistorted, 

 the outer edge may project over the inner hair cell, as in figure 7. 

 Then the fibrils supplied to this edge by the reclining cells of the 

 outermost part of the greater ridge may be traced to curve into 

 and around the edge, contributing to its rounded contour. 



The fibrils produced by the lesser ridge and attached to the 

 now thickened outer edge of the tectorial membrane, appear 

 drawn more straight by the growth of the membrane and appear 

 continuous with the 'peripheral condensation' of the apical sur- 

 face of the outer edge. These fibrils and the apical peripheral 

 condensations are considered above as homologous in that 

 both represent the product of the first activities of the cells, a 

 product less completely formed or organized than the body of 

 the tectorial membrane later produced by the cells of the greater 

 ridge. The fibrils, early formed by the lesser ridge, must con- 

 tribute but a very small part of Held's Decknetz, for it is hardly 

 possible, considering the physical character of the tectorial 

 membrane and the very evident delicacy of the fibrils, that they 

 can be pushed around and upon the apical surface of the mem- 

 brane. In figure 8, which represents a section of the 3rd half 

 turn of the cochlea of a pig of 19.5 cm., is indicated, I think, 

 the process of rupture and disintegration of the few and always 

 loosely associated fibrils produced by the lesser epithelial ridge. 



