686 



SPECIAL SENSES. 



The capsule of the lens is a thin, transparent membrane, which is very 

 elastic. This membrane generally is from 



FIG. 250. Crystalline lens ; anterior view (Babuchin). 



to -j-g^ of an inch (10 to 

 17 /i) thick; but it is very 

 thin at the periphery, meas- 

 uring here only eo * 0() of an 

 inch (4 /A). Its thickness is 

 increased in old age. The 

 anterior portion of the cap- 

 sule is lined on its inner sur- 

 face with a layer of exceed- 

 ingly delicate, nucleated epi- 

 thelial cells. The posterior 

 half of the capsule has no 

 epithelial lining. The cells 

 are regularly polygonal, 

 measuring ^W to -rho of 

 an inch (12 to 20 //,) in di- 

 ameter, with large, round 

 nuclei. After death, they 

 are said to break down into 



i i i ^ i i 



a liquid, known as the liquid 

 of Morgagni, though by some this liquid is supposed to be exuded from the 

 substance of the lens. At all events, the cells disappear soon after death. 



If the lens be viewed entire with a low 

 magnifying power, it presents upon either of 

 its surfaces, a star with nine to sixteen radi- 

 ations extending from the centre to about 

 half or two-thirds of the distance to the pe- 

 riphery. The stars seen upon the two surfaces 

 are not coincident, the rays of one being situ- 

 ated between the rays of the other. In the 

 foetus the stars are more simple, presenting 

 only three radiations upon either surface. 

 These stars are not fibrous, like the rest of 

 the lens, but are composed of a homogeneous 

 substance, which extends, also, between the 

 fibres. 



The greatest part of the substance of the 

 lens is composed of very delicate, soft and plia- 

 ble fibres, which are transparent, but perfect- 

 ly distinct, These fibres are flattened, six- 



sided prisms, Closely packed together, SO that 



their transverse section presents a regularly 



tesselated appearance. They are y^ to -^-^ 



and y^^rg- to &Q 1 A of an inch (2 to 3 p.) in thickness. Their flat surfaces are 



parallel with the surface of the lens. The direction of the fibres is from 



251.-Secti^n of ^crystalline lens 



of an inch (5 to 10 /x) broad, 



