The Nervous System 147 



The choroid is very closely united on the outside 

 with the sclera; on the inside it is less closely at- 

 tached to the retina except at the ora serrata. It 

 consists of an outer fibrous coat, an inner, unstrati- 

 fied pigmented epithelium derived embryologically 

 from the pigmented layer of the retina, and the 

 ground substance which is a network of irregular 

 and very vascular cells. 



As in probably all reptiles there is present in 

 the Crocodilia a vascular pigmented fold of the 

 choroid, the pecten, which projects into the middle 

 of the cavity of the eyeball. 



In the retina Bronn describes the following ten 

 layers, which are those commonly given in other 

 vertebrate retinas: (i) the inner limiting mem- 

 brane, (2) optic fiber layer, (3) ganglion cell layer, 

 (4) inner granular layer, (5) inner nuclear layer, (6) 

 outer granular layer, (7) outer nuclear layer, (8) 

 outer limiting membrane, (9) cone layer, (10) 

 pigmented layer. The Crocodilia differ from prob- 

 ably all other reptiles in having rods as well as 

 cones in the retina. The rods are more numerous 

 except in the neighborhood of the fovea centralis 

 where the cones predominate; in the fovea itself 

 only cones are found. 



The lens does not show any characteristics 

 unusual enough to warrant special description. 



The Ear. The ear is of special interest here 

 because it is in the Crocodilia that are first found 

 the three distinct regions of the ear that are seen 



