No. I.] THE VERTEBRATE EAR. 



39 



Alligator (PL VII, Figs. 2, 4, 7, and 9 ; PI. X, Figs. 3 and 4). 



The sense organ of the basilar portion of the cochlea is com- 

 posed of two groups of cells, or two epithelial ridges, which run 

 nearly parallel with each other. There are other epithelial 

 ridges which, however, do not seem to contain sensory cells 

 (Fig. 3, e.eJ). The larger or middle ridge is the most prom- 

 inent part of the organ, and is the homologue of the small 

 epithelial ridge of the Mammal ear ; the inner ridge {l.e.r.) is 

 the homologue of the larger epithelial ridge of the Mammal 

 embryo and bears, especially on its outer border, hair cells sim- 

 ilar to those covering most of the smaller epithelial ridge ; but 

 whether its entire surface bears cells auditory in function re- 

 mains to be determined. 



The middle region of this ridge has near its inner border sev- 

 eral rows of large hair cells, which vary in number with the 

 place from which the section is taken. At the extreme ends 

 no cells are seen, yet on advancing toward the middle of the 

 ridge the hair cells appear, first as a single row, then double, 

 triple, quadruple, quintuple, and on up to eight neighboring cell 

 rows near the middle of the papilla. 



These very remarkable cells are the large hair cells and occupy 

 the inner border, while the remainder of the papilla is made 

 up, or, more correctly, covered over with the smaller hair cells. 

 But above and below the middle of the papilla the rows num- 

 ber eight to ten, while in the middle part of the sensory patch 

 there are found as many as twenty cells in transverse section. 



The sensory epithelium is supported by a lamina reticularis, 

 which rapidly fades away towards the sides. As one nears the 

 large hair cells the meshes become incomplete. This reticular 

 membrane is especially pronounced in osmic preparations, 

 scarcely visible in Miiller preparations, and here as elsewhere 

 it is an artifact. 



The supporting cells are long and irregularly cylindrical cells, 

 which reach from the surface of the basilar papilla quite to the 

 basilar membrane upon which they are inserted. They bear 

 their nuclei in the basal portions of their cell bodies. They 

 are loosely placed, with considerable interspaces between the 

 cells. 



Retzius concluded that neither representatives nor develop- 



