66 THE EYE. 



Epithelium of the capsule. At the back of the lens the fibres are directly in 

 contact with the inner surface of the capsule, but in front they are separated from 

 the latter by a single layer of cubical, polygonal, nucleated cells, which covers the 

 whole anterior surface underneath the capsule. Towards the edge or equator of 

 the lens the appearance and character of these cells undergo a change : they first 

 gradually take on a columnar form, and then, becoming more and more elongated, 

 present every transition to the nucleated lens-fibres of the superficial layers, into 

 which they are directly continuous (see fig. 76). 



After death a small quantity of fluid (liquor Morgagni) frequently collects 

 between the back of the lens and the capsule : it appears to be derived from the 

 lens-fibres. There is no epithelium in this situation as in front. 



Changes in the lens with age. In the fcatus, the lens is nearly spherical 

 (fig. 77, a) : it has a slightly reddish colour, is not perfectly transparent, and is 

 softer and more readily broken down than at a more advanced age. 



i C 



^ Fig. 77. SIDE VIEW OF THE LENS AT DIFFERENT AGES. 



, at birth with the deepest convexity ; b, in adult life with medium 

 convexity ; c, in old age with considerable flattening of the curvatures. 



In the adult, the anterior surface of the lens is distinctly less convex than the 

 posterior (fig. 77, b) ; and the substance of the lens is firmer, colourless, and 

 transparent. 



In old aye, it is more flattened on both surfaces (c) ; it assumes a yellowish or 

 amber tinge, and is apt to lose its transparency and gradually to increase in 

 toughness and specific gravity. 



AQUEOUS HUMOUR AND ITS CHAMBER. 



The aqueous humour fills the space in the fore part of the eyeball, between the 

 capsule of the lens with its suspensory ligament and the cornea. The iris, resting 

 in part upon the lens, divides the aqueous chamber partially into two, named 

 respectively the anterior and posterior chambers. This subdivision is incomplete in 

 the adult, but in the foetus before the seventh month it is completed by the mein- 

 brana pupillaris, which, by its union with the margin of the pupil, closes the 

 aperture of communication between the two chambers. 



The anterior chamber is limited in front by the cornea and behind by the iris, 

 while opposite the pupil it is bounded by the front of the lens and its capsule. 



The posterior chamber lies behind the iris. It js continuous through clefts in 

 the anterior part of the suspensory ligament of the lens with the triangular space 

 intervening between the margin of the lens, the anterior surface of the vitreous 

 humour and the ciliary body (canal of Petit), and it sends prolongations or pouches 

 between the zonula and the pars ciliaris retinae, as has already been described 

 (p. 62). The aqueous humour is a clear watery fluid, in which a few leucocytes 

 can sometimes be found. It is probably secreted mainly by the epithelium of the 

 ciliary body and its glands, and by the epithelium covering the posterior surface of 

 the iris. It finds exit through the clefts of the ligamentum pectinatum iridis, 

 into the spaces of Fontana and thence into the canal of Schlemm and the venous 

 system of that region, and in part into lymph-spaces in the iris, and thence to the 

 perichoroideal lymph-space. 



