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: (1) 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 
