112 



THE GENESIS OF THE VERTEBRATE EYE 



planes, creating an unsutured cortex overlying a sutured core, the cortex 

 becoming proportionately thinner as the lens ages and the rate of fiber- 

 formation is slowed (see also pp. 20-1). 



Fig. 42 — The hyaloid circulation. 



a, model of invaginating mammalian optic vesicle, showing future hyaloid artery being taken 

 up through the embryonic fissure. Based upon figures of Mann. 



bw- brain wall; ca- carotid artery; cv- first chonoidal vessels, which will anastamose around 

 cup rim to form the annular vessel, and will branch over cup surface to lay down the 

 choriocapillaris; ha- hyaloid artery. 



b, model of fetal mammalian eye in optical section, showing the hyaloid system at the peak 

 of its development. Based upon figures of Versari. 



ac- anterior chamber; av- annular vessel; hp- Bergmeister's papilla (neuroglial support at 

 base of hyaloid, which will later atrophy with the hyaloid vessels, leaving a cup in the 

 nerve head); c- cornea; cc- choriocapillaris (first vessels of the chorioid to form); Ad- 

 trunk of hyaloid artery, traversing vitreous cavity; im- ins mesoderm, containing capillary 

 arcades thrown forward from annular vessel; /- lens; mc- mesenchymal (mesodermal) con- 

 densation which will form chorioid and sclera; p- lids (temporarily fused over cornea); 

 pe- pigment epithelium of retina; r- retina, with neuroblastic layer still single anteriorly 

 but already divided into inner and outer layers in the precocious fundal region; tvl- vessels 

 of tunica vasculosa lentis, encapsulating the growing lens; vhp- vasa hyaloidea propria, 

 supplymg the vitreous and the retinal surface — the last vessels of the system to differ- 

 entiate, and usually the first to atrophy. 



This growth process never completely stops until death, though it is 

 greatly retarded after the eye has reached its adult size. The oldest fibers 

 of the lens being the innermost ones, it is these which first feel the effects 

 of being removed farther and farther from any possible source of food 

 and oxygen, and they sclerose (harden) and die. The sclerosis involves 



