CH. LV.] 



THE LENS. 



747 



The lens is made up of a series of concentric laminae (fig. 567), 

 which, when it has been hardened, can be peeled off like the coats of 

 an onion. The laminae consist of long ribbon-shaped fibres, which 

 in the coilrse of development have originated from cells. 



The fibres near the margin have nuclei and are smooth, those 

 near the centre are without nuclei 

 and have serrated edges. They are 

 hexagonal in transverse section. The 

 fibres are united together by a scanty 

 amount of cement substance. The 

 central portion (nucleus) of the lens 

 is the hardest. 



The epithelium of the lens consists 

 of a layer of cubical cells anteriorly, 

 which merges at the equator into 

 the lens fibres. The development 

 of the lens explains this transition. 

 The lens at first consists of a closed 

 sac composed of a single layer of 

 epithelium. The cells of the pos- 

 terior part soon elongate forwards and obliterate the cavity ; 

 the anterior cells do not grow, but at the edge they become con- 

 tinuous with the posterior cells, which are gradually developed 

 into fibres (fig. 568). The principal chemical constituent of the 

 lens is a proteid of the globulin class called crystallin. 



Corneo-scleral junction. At this junction the relation of parts 

 (fig. 565) is so important as to need a short description. In this 



Fig. 567. Laminated structure of 

 the crystalline lens. Thelaminee 

 are split up after hardening in 

 alcohol, i, the denser central part 

 or nucleus ; 2, the successive ex- 

 ternal layers. }. (Arnold.) 



Fig. 568. Meridional section through the lens of a rabbit, i, Lens capsule ; 2, epithelium 

 of lens ; 3, transition of the epithelium into the flbreti ; 4, lens fibres. (Bubuchin.) 



neighbourhood, the iris and ciliary processes join with the cornea. 

 The proper substance of the cornea and the posterior elastic 

 lamina become continuous with the iris, at the angle of the iris, 

 and the iris sends forwards processes towards the posterior elastic 

 lamina, forming the ligamentum pectinatum iridis, and these join 

 with fibres of the elastic lamina. The epithelial covering of the 

 posterior surface of the cornea is, as we have seen, continuous 

 over the front of the iris. At the iridic angle, the compact inner 

 substance of the cornea is looser, and between the bundles are 



