THE VITREOUS BODY. 603 



round its margin to unite with twigs from the ciliary processes 

 upon the anterior surface. The loops -of the latter gradually retire 

 from the centre towards the margin, and finally the posterior layer 

 also ceases to be vascular. In inflammatory conditions, however, 

 the vascularity may return. 



Uses. The crystalline lens is of the highest importance as one 

 of the refracting media of the eye. 



The fibres of the crystalline lens are, apparently, developed ori- 

 ginally from cells like those shown in Fig. 432. 



The groivth of the lens is, probably, secured by the absorption, 

 through its capsule, of the aqueous or the vitreous humor. (Kol- 

 tiker.) 



The crystalline lens has been, though very rarely, regenerated, 

 in very young subjects, after its entire extraction. 



An opacity of the crystalline lens, or its capsule, or both at the 

 same time, constitutes cataract. 



2. The Vitreous Body. 



This body (Figs. 426 and 431) is a close web of transparent 

 fibres, enveloping a transparent fluid in its meshes ; and is inclosed 

 in a simple membrane (membrana hyaloidea), on the exterior of 

 which vessels are distributed. (Todd and Bowman?) The central 

 artery of the retina passes through the centre of the vitreous body, 

 but does not give off' any branches to it. Its nourishment is pro- 

 bably in part sustained by the plexiform arrangement of vessels 

 constituting the ciliary processes. (Fig. 430.) 



The fluid of the vitreous humor is a weak, watery solution of 

 salts and albumen. 



During foetal life, this body is supplied with vessels in its inte- 

 rior also. 



Use. This is also one of the refracting humors of the eye. 



The eyeball is covered anteriorly by the conjunctiva, which is 

 essentially a mucous membrane; though the portion in front of the 

 cornea is merely a compound scaly epithelium, without a corium. 

 This also continues over the sclerotica, where there is a pale, thin 

 corium, without any papillae, and attached to the sclerotic by a 

 loose and abundant areolar tissue containing fat-cells. The mem- 



