STRUCTURE OF THE LENS. 



65 



the fully -formed lens the nuclei have disappeared from the fibres which form the 

 more internal parts of the lens, and only remain in the more superficial layers. 



Fig. 76. SECTION THROUGH THE MARGIN OP THE LENS, 



SHOWING THE TRANSITION OP THE EPITHELIUM INTO 

 THE LENS-FIBRES (Bablichin). 



Here they are found, not quite in the middle of 

 each fibre, but slightly nearer the anterior end, 

 their situation nearly corresponding in adjacent 

 fibres, and they form by their juxtaposition the 

 so-called " nuclear zone " around the lens. The 

 superficial fibres further differ from the more 

 deeply seated ones in being softer and larger, and 

 in possessing a plain, unserrated margin. The 

 extremities of all the fibres are softer and more 

 readily acted on by reagents than the middle 

 parts, and the axial or more internal part of a 

 fibre more so than the external, but the transi- 

 tion is gradual from one to the other, and there 

 is no definite membrane enclosing each fibre. 

 The lens-fibres when cut across are seen to be 

 six-sided prisms (fig. 75 B). By reason of this 

 shape they fit very exactly the one to the other 

 with but little interfibrillar cementing substance 

 between. This is met with in rather larger 

 quantity in the intersecting planes between the 

 ends of the fibres. 



Thin and Ewart have shown that with certain 

 methods of treatment the superficial lens-fibres show 

 indications of being 1 composed of a number of regular 

 segments separated by sharply marked lines of inter - 

 segmental substance (Journal of Anatomy, 1876). 



The capsule of the lens is a transparent 

 structureless membrane ; somewhat brittle and 

 elastic in character, and when ruptured the 

 edges roll outwards. The fore part of the capsule, 

 from about 2*5 mm. from the circumference, 

 where the anterior part of the suspensory liga- 

 ment joins it, is much thicker than the back : 

 at the posterior pole of the lens the capsule is very 

 thin indeed. In the adult, it, like the lens itself, 

 is entirely non-vascular, but in the foetus there 

 is a network of vessels in the superficial part of 

 the capsule, supplied by the terminal branch of 

 the central artery of the retina, which passes 

 from the optic papilla through the canal of 

 Stilling in the vitreous humour to reach the 

 back of the capsule, where it divides into radiating branches. After forming 

 a fine network, these turn round the margin of the lens and extend forwards to 

 become continuous with the vessels in the pupillary membrane and iris (fig. 42, 

 p. 34). 



VOL. III., FT. 3. 



