XVII 



THE SENSE ORGANS 



327 



above, the choroid, and the retina. The choroid is a vas- 

 cular, pigmented layer lying next to the sclerotic. Next 



Cam. anter, 



Cam. post 



Cornea 



Corp. cil. 

 Ora optica 



Sclerae 



"^^--vjiO 



Fig. 89. — Section through the optical axis of the eye of the frog. Cam. 

 a»^(?A-, outer chamber containing the aqueous humor; Cam.post, inner 

 chamber containing the vitreous body ; Corp.cil, ciliary body ; Corp.vitr, 

 vitreous body; P.cartil. zx\.A P. fibrosa SclercB, c2iXX\\Agv!\ow% and fibrous 

 layers of the sclerotic coat; Zon.cil, zonula ciliaris, (From Gaupp, after 

 G. Retzius.) .^ 



within the choroid lies the retina which is continued ante- 

 riorly over the posterior surface of the iris as far as the pupil. 

 It is composed of two principal layers, an outer tliin layer 

 of pigmented cells, and an inner much thicker layer which 

 forms the sensitive portion of the retina. Over the ciliary 

 body and posterior side of the iris the retina is much thinner 

 than it is elsewhere and does not contain nervous tissue. 



