348 S. R. DETWILER AND HENRY LAURENS 



and crocodiles. According to hini, in the Crocodilia (Crocodilus 

 intenne'dius and Alligator mississippiensis) it is a simple striped- 

 shaped thickening with a faintly developed fovea in the form of 

 a narrow furrow, running across the retina about 1 mm. from 

 the lower margin of the tapetum. In the turtle, Emys europea, 

 the area is a round, thickened region lying above the entrance of 

 the optic nerve, and contains no fovea. In the snake, Tropi- 

 donotus natrix, Chievitz could not give the exact location of the 

 area because of lack of orientation of the eye; again no fovea 

 could be demonstrated. In Chameleon vulgaris the area is 

 described as lying 'behind' the entrance of the optic nerve ajid 

 containing a deep, highly developed fovea. Rochon-Duvig- 

 neaud ('17) also figures a maximally developed fovea in Chame- 

 leon. In Lacerta vivipara and Lacerta viridis, Chievitz de- 

 scribes the area as a rounded elevation situated just above the 

 entrance of the optic nerve. Both forms have a slightly devel- 

 oped fovea. Heinemann ('77) could find no fovea in the retinae 

 of Chelonians. Investigation by Detwiler ('16) of several rep- 

 tilian retinae revealed the absence of a fovea in Chelopus insculp- 

 tus and Chrysemys picta, although in both forms an area was 

 found as a shghtly thickened region above the entrance of the 

 optic nerve, more highly developed in Chrysemys than in Chelopus. 

 The retina of the lizard, Sceloporus undulatus, showed the pres- 

 ence of a prominently developed area with a deep conical fovea 

 lying above and slightly lateral to the entrance of the optic nerve. 



The area -centralis of Phrynosoma consists of a doubly-convex 

 circular thickening of the posterior portion of the retina, the 

 vitreal curvature of which is quite marked. It lies above the 

 entrance of the optic nerve (fig. 1) and contains a highly devel- 

 oped fovea (figs. 1 and 2). At its widest portion (including the 

 retinal pigment layer) the area has a thickness of 240 ^u; the 

 retina below the optic nerve at a typical region has a thickness 

 of 150 fx. 



Fovea. The fovea is a deep, cone-shaped depression with a 

 broad base, situated in the center of the area (figs. 1 and 3), its 

 apex being about 1.5 mm. above the entrance of the optic nerve. 

 At this point the thickness of the retina (pigment layer included) 



