No. I.] THE VERTEBRATE EAR. 203 



tween the cells at the surface of the papilla. They stand nearly 

 perpendicularly upon the basilar membrane, and at this stage 

 resemble the pillar cells in shape and histological features. 



The membrana tectoria lies upon the limbus spiralis and the 

 larger epithelial fold, and sometimes may be seen to reach as 

 far as the rows of the outer hair cells, though usually its edge 

 is found (especially in osmic and chromic acid preparations) 

 over the inner hair cells, thus leaving the outer hair cells and 

 the rows of pillar cells uncovered. 



The nervus cochlearis varies in its relations to the cochlea 

 with the increasing spiral twisting, which bends the ganglion 

 more and more, and thus displaces the cochlear fibres. The 

 fibres at this stage are mostly non-medullated, and are not to be 

 traced beyond their entrance into the sense organ except with 

 difficulty. 



2. In the Nezv Born. 



The large epithelial fold of the papilla acustica basilaris is not 

 raised from the wall of the ductus cochlearis. Its curved sur- 

 face declines gradually inwards, where it passes at an obtuse 

 angle into the surface of the small epithelial fold. The very 

 long cells of the large epithelial fold incHne inwards within, 

 stand perpendicularly in the middle, and incline outwards in the 

 outer part of the sense organ. 



Corti's pillars grow larger and broader very rapidly after birth. 

 They form two closely placed cell rows, which, however, are 

 completely separate and disunited. Their nuclei are large and 

 lie at bases of cells. The tunnel has not made its appearance 

 between them. 



The inner and outer hair cells are somewhat larger than in 

 the embryo ; otherwise they are the same as before birth. The 

 histological features of the cell protoplasm in the adult have 

 not yet begun to make their appearance. 



The membrana tectoria covers with its thicker portion the 

 large epithelial ridge, lying very close to the surface, and passing 

 over (as yet there is no trace of sulcus spiralis internus) the 

 large ridge, hangs free over the outer and inner hair cells, send- 

 ing fibrous prolongations to the hair cells of the papilla acustica 

 basilaris ; but these processes are not in any way connected 

 with the hairs of the hair cells ; on the contrary, the latter pro- 



