662 SPECIAL SENSES 



but is much thinner at the periphery, measuring here only g-^ of an 

 inch (4 //.). Its thickness is increased in old age. The anterior portion 

 of the capsule is lined on its inner surface with a layer of delicate nu- 

 cleated epithelium. The posterior half of the capsule has no epithelial 

 lining. The cells are regularly polygonal, measuring goW to 250 of 

 an inch (12 to 20 ft) in diameter, with large round nuclei. After death 

 they are said to break down into a liquid, known as the liquid of Mor- 

 gagni, 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 is viewed entire with a low magnifying power, it pre- 

 sents upon either of its surfaces, a star with nine to sixteen radiations 

 extending from the centre to about one-half or two-thirds of the distance 

 to the periphery. The stars seen on the two surfaces are not coinci- 

 dent, the rays of one being situated between the rays of the other. In 

 the foetus the stars are more simple, presenting only three radiations on 

 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 deli- 

 cate, soft and pliable fibres, which are transparent but perfectly dis- 

 tinct. These fibres are flattened six-sided prisms, closely packed 

 together, so that their transverse section presents a regularly-tessellated 

 appearance. They are -goVo to rsW ^ an mc ^ (5 to IO /*) broad, and 

 Tslhro to 9Wo f an i nc h ( 2 to 3 P) m 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 periph- 

 ery, where they turn and pass to the star of the opposite side. The 

 outer layers of fibres near the equator, or circumference of the lens, 

 contain distinct oval nuclei with one or two nucleoli. These become 

 smaller in passing more deeply into the substance of the lens and grad- 

 ually disappear. 



The regular arrangement of the fibres of the lens makes it possible 

 to separate its substance into laminae, which have been compared by 

 anatomists to the layers of an onion ; but this separation is artificial, 

 and the number of apparent layers depends largely on the dexterity of 

 the manipulator. It is to be noted, however, that the exernal portions 

 of the lens are soft, even gelatinous, and that the central layers are 

 much harder, forming a sort of central kernel, or nucleus. 



The lens is composed of a globulin, called crystallin, combined with 

 various inorganic salts. One of the constant constituents of this body 

 is cholesterin. In an examination of four fresh crystalline lenses of the 





