470 



EMBRYOLOGY. 



Finally outer and inner layers come to lie in close contact (fig. 266 

 pi and r). The fundaments of the lens {le and If) and the vitreous 

 body (g) constitute the contents of the cup. The vitreous body fills 

 the bottom of the cup, the lens its opening. 



In the process of invagination the stalk of the optic vesicle has 



^ig, 26f« — Section through the optic fundament of an embryo House, after Kessler, . 



pi, Pigmented epithelium of the eye (outer lamella of the optic cup, or secondary optic vesicle) ; 

 r, retina (inner lamella of the optic cup) ; rz, marginal zone of the optic cup, which forms 

 the pars ciliaris et iridis retinae ; g, vitreous body with blood-vessels ; tv, tunica vasculosa 

 lentis ; bk, blood-corpuscles ; ch, choroidea ; If, lens-fibres ; le, lens-epithelium ; V, zone of 

 the lens-fibre nuclei ; h, fimdament of the cornea ; /ig, external corneal epithelium. 



also changed its form. Originally it is a small tube with an epithe- 

 lial wall, but afterwards it becomes an inverted trough with double 

 walls, inasmuch as its lower surface participates in the invagination 

 caused by that growth of connective tissue which toward the peri- 

 phery furnishes the vitreous body. Later the edges of the trough 

 bend together and fuse with each other. In this way the connective- 



