714 



MANUAL OF PHYSIOLOGY. 



entiated the various layers of the retina, except the layer of pig- 

 ment cells which lies next to the choroid. The posterior layer 

 develops this layer of pigment cells, which, from their intimate 

 connection to the choroid, were formerly considered as part of 

 that membrane. 



Fio. 295. 



A further stage of the development of the lens. (Cadiat.) a, Elongating 

 epithelial cells forming lens; 6, Capsule ; c, Cutaneous tissue becoming con- 

 junctiva ; d, e, Two layers of optic cup forming retina ; /, Cell of mucous 

 tissue of the vitreous humor ; g, Intercellular substance ; h, Developing 

 optic nerve. 



The thickening of the inner or anterior layer of the optic cup 

 ceases at the ora serrata. The outer layer with its contiguous 

 choroid is thrown into a number of folds the ciliary processes 

 and, passing in front of the lens, helps to form the iris. 



In front of the ora serrata the anterior layer of the cup is no 



