DEVELOPMENT OF THE EYE. 



to the layer of rods and cones, while from the outer thinner layer the hexagonal 

 pigmented epithelium of the retina, with its continuation into the uvea, is formed. 

 The inyagination of the primary optic vesicle does not occur only opposite the 



Fig. 96. PAET OF A SECTION THROUGH THE 



HEAD OF AN EARLY HUMAN EMBRYO, SHOWING 

 THE CONNECTION OF THE PRIMARY OPTIC VESI- 

 CLES WITH THE FOREBRAIN. (His. ) 



olf, olfactory area of epiblast ; c.h, part of 

 forebrain which gives rise to cerebral hemi- 

 spheres ; tli, thalamencephalon ; p.o.v, primary 

 optic vesicles. 



Fig. 97. SECTION THROUGH THE SAME PART OF A 



MORE ADVANCED EMBRYO, IN WHICH THE LENS IX- 

 VAGINATION IS FORMED, AND THE PRIMARY OPTIC 

 VESICLES ARE CUPPED. (His.) 



o.c, optic cup ; o.s, optic stalk ; I, lens invagina- 

 tion ; c.h, cerebral hemispheres ; th, thalameucepha- 

 lon ; i, infundibulum ; olf, olfactory area. 



C.CJOr-, 



Fig. 98. VERTICAL SECTION THROUGH THE MIDDLE OF THE DEVELOPING EYE OF A CHICK OF THE 



THIRD DAY. (E. A. S. ) 



The section passes longitudinally through the deficiency in the lower part of the optic cup, and 

 shows the mesoblast extending in between the lens invagination and the pigment layer of the optic cup. 



thai, thalamencephalon ; n.ep, neural epiblast; c.ep, cutaneous epiblast; o.s., optic stalk ; 0,0, 

 cavity of primary optic vesicle ; me, mesoblast ; v, mesoblast passing behind lens to form vitreous ; 

 /, lens invagination. 



Fig. 99. SECTION THROUGH THE EYE AND OPTIC STALK OF A HUMAN EMBRYO OF FIVE WEEKS. (His.) 



JF.c., connection of optic stalk with thalamencephalon ; Sp, cleft or fold in the stalk, where the 

 arteria centralis retinae passes in ; P, pigment layer ; R, retina ; L, lens. 



