388 DEVELOPMENT OF ORGANS IN MAMMALIA. [CHAP, 



cavity of the vitreous humour (Fig. 128 acr). The sides 

 of the optic nerve subsequently bend over, and com- 

 pletely envelope this artery, which then gives off 



FiQ. 128. 



rt 



a. c. r J^_g, 



{)/[)/! 71- 



rn e. o 



Section iheough the Eye of a Babbit Embbto op about 

 Twelve Days. 



0. epithelium of cornea : I. lens ; mec. meaoblast growing in from 

 the side to form the cornea ; rt. retina ; a.c.r. arteria cen- 

 tralis retinsB ; o/.n. optic nerve. 



The figure shews (1) the absence at this stage of mesoblast 

 between the lens and the epiblast ; the interval between the 

 two has however been made too great ; (2) the arteria centralis 

 retinae forming the vascular capsule of the lens and continuous 

 with vascular structures round the edges of the optic cup. 



