AND THE CRISTA SPIRALIS OF THE COCHLEA. 75 



The same figure shows also the extent of shrinkage often produced by fixing agents 

 through artificial distention of the more fluid part of the recently formed layer (////') 

 of the membrana tectoria. 



Coyne and Cannieu describe the membrana Corti as by no means formed by a 

 homogeneous clear substance with dense fibrils, but by membranes or sheets ("cloi- 

 sons") of a special nature circumscribing polygonal cavities which form a network 

 in perpendicular sections. "The surfaces of junction of these membranes thickened 

 at the angles of the reticulum" (p. 280) represent the alleged fibers; and on page 285 

 they add: "these sheets circumscribe polygonal cavities which gradually become 

 narrower from the organ of Corti toward the prominence of Huschke. " 



My results upon the development of the membrana tectoria are chiefly com- 

 parable with those of Prentiss. On page 442 this author states: 



"To sum up the development of the membrana previous to fetuses of 15.0 cm., we 

 may say that it is a cuticular organ with a definite though irregularly chambered structure 

 which is secreted between, and at the ends of the cells composing the basal epithelium of 

 the cochlea. " 



In his conclusion Prentiss adds : 



"In sections through the axis of the cochlea the membrana has a striated or lamellated 

 appearance. ... In sections perpendicular to the lamellae the structure of the mem- 

 brana is that of a reticulum with thickenings at the angles of the meshes. It is therefore 

 neither lamellar nor reticular but a chambered structure or ' honeycomb ' of hollow tapering 

 cuticular tubes or chambers normally filled with a fluid resembling the endolymph. The 

 bases of chambers during development rest between the ends of the epithelial cells." 



The main difference between the results of Prentiss and my own is that accord- 

 ing to my investigations there may exist an interprismatic substance among the 

 chambers, and that the walls of the cylinders are produced by the terminal bars 

 which were not recognized by Prentiss, while their content alone is formed by the 

 cytoplasmic apices of the cells. 



ON THE SURFACE OF THE LESSER EPITHELIAL RIDGE. 



Figure 28 displays a section tangential to the surface of the organ of Corti, 

 the neighboring greater ridge and a segment of the crista spiralis between the second 

 and third turn of the cochlear duct in a new-born dog. Ih and oh', oh", oh'" show 

 respectively the row of inner hair-cells and the three rows of outer hair-cells. Two 

 hair-cells, oh iv , belong to an interrupted fourth row of outer sensorial elements. 

 This segment of the section and another (mg, the superficial mosaic of the greater 

 ridge) are not in focus; therefore they are blurred, but the structures of the mem- 

 brana tectoria are plainly visible on the right of the figure. In continuity with 

 the rows of outer hair-cells one sees three different, more superficial planes s' , s", 

 s'". The first (s') displays horseshoe-like elements, the bases of the acoustic hairs; 

 they occupy more or less the center of clear areas separated by a system of darker, 

 thick, longitudinal lines (I) and of thinner transverse lines (/'). Some of these lines 

 are double and short bridges connect the two halves. The clear areas undoubtedly 

 correspond to the sensorial round fields of the outer hair-cells and overlie their 



