THE KETINA. 



713 



sule of the lens has been variously considered as arising from the 

 cells of the lens substance, or as originating from a thin layer of 



Diagrammatic section of the primitive eye, showing the choroidal fissure. 

 (Foster and Balfour.) D. Horizontal section. E. Vertical transverse sec- 

 tion just striking the posterior part of the lens. F. Vertical longitudinal 

 section through the optic stalk, and the fissure through which the mesoblast 

 passes to form the vitreous humor, h. Superficial epiblast. x. Point of 

 origin of the lens. v.h. Vitreous humor, r. Anterior layer of the optic 

 vesicle, u. Posterior layer of the optic vesicle, c. Cavity of the optic 

 vesicle. /. Choroidal fissure, s. Optic stalk. s f . Cavity of the optic stalk. 

 1. Lens. V. Cavity of the lens. 



mesoblast, which forms not only the lens capsule, but also the 

 hyaloid membrane, which is continuous with it. 



FIG. 294. 



Later stages in the development of the lens. (Cadiat.) a. Epiblast. 

 c. Eudimentary lens. o. Optic vesicle. 



The optic cup gives origin to the retina. The inner or an- 

 terior layer of the cup becomes thickened, and from it are differ- 



60 



