THE LEXS. 733 



THE LENS AND ITS CAPSULE. 



The lens, enclosed in a capsule, is situated behind the pupil, and in front 

 of the vitreous body. 



The capsule of the lens, a transparent glass-like membrane closely sur- 

 rounding the contained body, is hard and brittle, especially in front, but 

 very elastic and permeable to fluid. The anterior surface is in contact with 

 the iris towards the pupil, and recedes from it slightly at the circumference ; 

 the posterior rests closely on the vitreous body. Around the circumference 

 is a space to be afterwards noticed, the canal of Petit. The fore part of the 

 capsule is several times thicker than the back, as far out as to -y^-th of an 

 inch from the circumference, where the suspensory ligament joins it ; but 

 beyond that spot it becomes thinner, and it is thinnest behind. Tn its nature 

 the capsule of the lens resembles the glassy membrane at the back of the 

 cornea, for it is structureless, and remains transparent under the action of 

 acids, alcohol, and boiling water ; and when ruptured, the edges roll up 

 with the outer surface innermost. (Bowman.) 



Connecting the anterior wall of the capsule closely to the lens is a single layer of 

 granular and nucleated polygonal cells, which ends abruptly where the capsule comes 

 in contact with the hyaloid membrane. The place of termination of this cellular 

 layer round the margin of the lens corresponds to the line from which the fibres of 

 the lens are developed. There is no such layer of cells on the posterior wall of the 

 capsule, but in hardened specimens various reticulated appearances may be detected, 

 which probably arise, as supposed by Henle, from the pressure one on another of glo- 

 bules of a fluid separated from the lens after death, and known as liquor Morgagni. 



No vessels enter the capsule of the lens in the adult. In the foetus it receives an 

 artery behind, which is named the capsular artery. This vessel leaves the arteria 

 centralis retinae at the centre of the optic nerve, and passing through the substance of 

 the corpus vitreum, enters the posterior portion of the capsule of the lens, where it 

 divides into radiating branches. These form a fine network, turn round the margin of 

 the lens, and extend forwards to become continuous with the vessels in the pupillary 

 membrane and the iris. 



Some authors (Albinus, Zinn, &c.) state that they have traced vessels from the 

 capsule into the substance of the lens itself. 



THE LENS. 



The lens (lens crystalliua) is a doubly convex transparent solid body, with 

 a rounded circumference. Its convexity is not alike on the two surfaces, 



Fig. 483. LAMINATED STRUCTURE OF THE CRYSTAL- Fig. 483. 



LINE LENS (from Arnold). * 



The laminae are split up after hardening in alcohol. 

 1, the denser central part or nucleus; 2, the succes- 

 sive external layers. 



being greatest behind, and the curvature is 

 less at the centre than towards the margin. 

 It measures about ^rd of an inch across, and 

 ^-th from before backwards. In a fresh lens 

 the outer portion is soft and easily detached ; 

 the succeeding layers are of a firmer consis- 

 tence ; and in the centre the substance becomes 



much harder, constituting the nucleus. On the anterior and posterior 

 surfaces are faint white lines directed from the poles towards the cir- 

 cumference ; these in the adult are somewhat variable and numerous on 



