AQUEOUS HUMOR. VITREOUS BODY, ETC. 689 



foetus before the seventh month, when the pupil is closed by the membrana 

 pupillaris, the two chambers are quite separate. 



It has been generally supposed that the two chambers are lined by a distinct 

 membrane, the secreting membrane of the aqueous humor, analogous in struc- 

 ture to that of a serous sac. An epithelial covering can, however, only be found 

 on the posterior surface of the cornea. That the two chambers do, however, 

 secrete this fluid separately, is shown from its being found in both spaces before 

 the removal of the membrana pupillaris. It is probable that the parts concerned 

 in the secretion of the fluid, are the posterior surface of the cornea, both surfaces 

 of the iris, and the ciliary processes. 



VITREOUS BODY. 



The Vitreous Body forms about four-fifths of the entire globe. It fills the 

 concavity of the retina, and is hollowed in front for the reception of the lens 

 and its capsule. It is perfectly transparent, of the consistence of thin jelly, and 

 consists of an albuminous fluid inclosed in a delicate transparent membrane, 

 the hyaloid. This membrane invests the outer surface of the vitreous body ; it 

 is intimately connected in front with the suspensory ligament of the lens ; and 

 is continued into the back part of the capsule of the lens. It has been sup- 

 posed, by Hannover, that from its inner surface numerous thin lamella? are 

 prolonged inwards, in a radiating manner, forming spaces in which the fluid is 

 contained. In the adult, these lamellae cannot be detected even after careful 

 microscopic examination ; but in the foetus a peculiar fibrous texture pervades 

 the mass, the fibres joining at numerous points, and presenting minute nuclear 

 granules at their point of junction. The fluid from the vitreous body resembles 

 nearly pure water ; it contains, however, some salts, and a little albumen. 



In the foetus, the centre of the vitreous humor presents a tubular canal, through 

 which a minute artery passes along the vitreous body to the capsule of the lens. 

 In the adult, no vessels penetrate its substance ; so that its nutrition must be 

 carried on by the vessels of the retina and ciliary processes, situated upon its 

 exterior. 



CRYSTALLINE LENS AND ITS CAPSULE. 



The Crystalline Lens, inclosed in its capsule, is situated immediately behind 

 the pupil, in front of the vitreous body, and surrounded by the ciliary processes, 

 which slightly overlap its margin. 



The capsule of the lens is a transparent, highly elastic, and brittle membrane, 

 which closely surrounds the lens. It rests, behind, in a depression in the fore 

 part of the vitreous body : in front, it forms part of the posterior chamber of 

 the eye ; and it is retained in its position chiefly by the suspensory ligament of 

 the lens. The capsule is much thicker in front than behind, structureless in 

 texture ; and when ruptured, the edges roll up with the outer surface inner- 

 most, like the elastic lamina of the cornea. The lens is connected to the inner 

 surface of the capsule by a single layer of transparent, polygonal, nucleated 

 cells. These, after death, absorb moisture from the fluids of the eye; and, 

 breaking down, form the liquor Mbryagni. 



In the foetus, a small branch from the arteria centralis retinas runs forwards, 

 as already mentioned, through the vitreous humor to the posterior part of the 

 capsule of the lens, where its branches radiate and form a plexiform network, 

 which covers its surface, and are continuous round the margin of the capsule 

 with the vessels of the pupillary membrane, and with those of the iris. In the 

 adult no vessels enter its substance. 



The lens is a transparent, double-convex body, the convexity being greater 

 on the posterior than on the anterior surface. It measures about a third of an 

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