504 



THE CIIOROID FISSURE. 



nerve, passes through the choroid slit into the cavity of the vitreous humour 

 (fig. 295, acr). The sides of the optic nerve subsequently bend over, and 

 completely envelope this artery, which at a later period gives off branches to 

 the retina, and becomes known as the arteria centralis retinas. It is 

 homologous with the arterial limb of the vascular loop projecting into the 

 vitreous humour in Birds, Lizards, Teleostei, etc. 



Before becoming enveloped in the optic nerve this artery is continued 

 through the vitreous humour (fig. 295), and when it comes in close proximity 



a. c. 



,m, e o 



FIG. 295. SECTION THROUGH THE EYE OF A RABBIT EMBRYO OF 



ABOUT TWELVE DAYS. 



c. epithelium of cornea ; /. lens ; mec. mesoblast growing in from the side to form 

 the cornea: rt. retina ; a.c.r. arteria centralis retinae; of.n. optic nerve. 



The figure shews (i) 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. 



to the lens it divides into a number of radiating branches, which pass round 

 the edge of the lens, and form a vascular sheath which is prolonged so as to 

 cover the anterior wall of the lens. In front of the lens they anastomose 

 with vessels, coming from the iris, many of which are venous (fig. 295) and 

 the whole of the blood from the arteria centralis is carried away by these 

 veins. The vascular sheath surrounding the lens receives the name of the 

 membrana capsulo-pupillaris. The posterior part of it appears (Kessler, 

 No. 372) to be formed of vessels without the addition of any other structures 

 and is either formed simply by branches of the arteria centralis, or out of 



