62 SPECIAL SENSES. 



the lens itself being composed of layers of fibres of different 

 degrees of density. 



The capsule of the lens is an exceedingly thin, transpar- 

 ent membrane, very elastic, so that when it is torn, the force 

 of its contraction frequently expels its contents. This mem- 

 brane is generally from 2 / 00 to Ig 1 0o of an inch thick ; but 

 it is very thin at the periphery, measuring here only ^^Q of 

 an inch. Its thickness is increased in old age. On the ante- 

 rior portion, the capsule is lined with a layer of exceedingly 

 delicate, nucleated epithelial cells. These are situated on the 

 inner surface of the membrane. The posterior half of the 

 capsule has no epithelial lining. The cells are regularly po- 

 lygonal, from -g-gVo" * TsVir ^ an mcn m diameter, with large, 

 round nuclei. After death they are said to break down into 

 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 from nine 

 to sixteen radiations extending from the centre to about half 

 or two-thirds of the distance to the periphery. The stars 

 seen upon the two surfaces are not coincident, the rays of 

 one being situated between the rays of the other. In the foe- 

 tus, the stars are more simple, presenting only three radia- 

 tions 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 com- 

 posed of very delicate, soft, and pliable fibres, which are trans- 

 parent, but perfectly distinct. These fibres are flattened, six- 

 sided prisms, closely packed together, so that their transverse 

 section presents a regularly-tesselated appearance. They are 



f rom TsW to imnr of an mcn broad and from Ig ^ o0 to -^Vir of 

 an inch in thickness. Their flat surfaces are parallel with 

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

 the centre and from the rays of the stellate figures to the 



