THE EYE. 



709 



and a vascular coat, the choroid, which lies in contact with the 

 outer layer of the optic cup. 



In front of the lens, beneath the epiblast, the mesoblast forms 



Diagrammatic section of the primitive eye, showing the choroidal fissure (Foster and 

 Balfour). D. Horizontal section. E. Vertical transverse section just striking the pos- 

 terior part of the lens. F. Vertical longitudinal section through the optic stalk, and the 

 fissure througli which the mesoblast passes to form the vitreous humor, h. Superficial 

 epiblast. x. Point of origin of the lens. r.A. Vitreous humor, r. Anterior layer of the 

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

 Choroidal fissure. *. Optic stalk, t'. Cavity of the optic stalk. I. Lens. /'. Cavity of 

 the lens. 



the corneal tissue proper. The epiblast forms the epithelial or 

 conjunct! val covering of the eyeball. 



The involution of mesoblast through the choroidal fissure, 

 which forms the vitreous humor, indents the optic stalk, and 



FIG. 294. 



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

 lens. o. Optic vesicle. 



forms the central artery of the retina. The choroidal fissure is 

 gradually obliterated, and its position may sometimes be marked 

 by a permanent fissure in the iris (coloboma iridis). 



