780 



SPECIAL SENSES. 



The capsule of the lens is an exceedingly thm> transparent membrane, very elastic, so 

 that, when it is torn, the force of its contraction frequently expels its contents. This 

 membrane is generally from ^Vo to ^7 of an inch thick ; but it is very thin at the 

 periphery, measuring here only ^ of an inch. Its thickness is increased in old age. 

 On the anterior portion, the capsule is lined with a layer of exceedingly delicate, nucle- 

 ated 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 polygonal, 

 measuring from ^Vo to T1J Vs of an inch in 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 



FIG. 247. Crystalline lens, posterior view. (Babuchin.) 



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 foetus,the stars are more simple, presenting only three radiations upon either sur- 

 face. These stars are not fibrous, like the rest of the lens, but are composed of a homo- 

 geneous substance, which extends, also, between the fibres. 



The greatest part of the substance of the lens is composed of very delicate, soft, and 

 pliable fibres, which are transparent, but perfectly distinct. These fibres are flattened, 

 six-sided prisms, closely packed together, so that their transverse section presents a regu- 

 larly-tesselated appearance. They are from T -gVo to ^Vs of an incn broad and from 

 TTOTO to -roV? f an m ch 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 periphery, where they turn and pass to the star upon the opposite 

 side. The outer layers of fibres, near the equator, or circumference of the lens, are pro- 

 vided with exceedingly distinct, oval nuclei, with one or two nucleoli. These become 

 smaller as we pass deeper into the substance of the lens, and gradually they disappear. 



The regular arrangement of the fibres of the lens makes it possible to separate its 

 substance into lamina, which have been compared by anatomists to the layers of an 

 onion ; but this separation is entirely artificial, and the number of apparent layers depends 



