No. I.] THE VERTEBRATE EAR. 95 



ered by a cutictila, the beginning of the membrane of Corti, 

 which first appears on the median wall. It is quite thick for 

 about half its breadth, and simply covers the outer supporting 

 cells. Loewenberg's statement that Corti's membrane is in- 

 serted into the outer wall of the cochlear canal is incorrect. 



Boettcher (1869, 31) gives a histological account of the de- 

 velopment of Corti's organ, in which he describes the onto- 

 genetic changes of this much-studied structure in detail as 

 follows : — 



Corti's membrane appears early in development as a thin, 

 radiately striated skin {Hdiitcheii) or membrane, lying close 

 upon the epithelium of the lower wall of the cochlear tube, the 

 thickest portion of which is near the inner edge. In the fully 

 developed condition the membrane appears, when studied fresh, 

 obliquely striated from within outward, diagonally upwards, i.e. 

 towards the apex of the helix. It seems to be soft and yielding, 

 but extremely elastic. At this time it is divisible into three 

 zones. The inner zone begins at the inner angle of the cochlear 

 canal and stretches across to the free border of the labium 

 vestibulare. It is thin at its inner border, but grows thicker 

 towards its outer edge. On its surface one finds even in new- 

 born animals roundish or angular pits or grooves, which impres- 

 sions are cell contours. In older individuals it is the teeth and 

 ridges of Corti's organ which give the markings to the surface. 

 The second zone is thick and has strong striation, and it reaches 

 to the vicinity of the pillars of Corti. In the embryo it lies 

 upon the large epithelial ridge. It grows thinner outwards, 

 ending in fibrous prolongations that are continuous with (enter 

 into connection with) the membrana reticularis, its whole outer 

 border being divided up into ribs by means of vertical parallel 

 incisions. Each rib sends downwards a fibrous, later divided 

 process, a branch from which goes to the inner hair cell, where- 

 as the other passes out over the three rows of Corti's cells and 

 gives off to each an abruptly descending branch and then con- 

 nects with the neighboring epithelial cells. 



Corti's membrane is also in continuity by means of fibrous 

 processes with the upper inner as well as with the outer de- 

 scending hair cells. Whether these processes penetrate further 

 into the cells cannot be determined. The hairs or rods of the 

 auditory cells are consequently artifacts originating in the tear- 



