ANATOMY OF THE EYEBALL. 63 



periphery, where they turn and pass to the star upon the oppo- 

 site side. The outer layers of fibres, near the equator, or cir- 

 cumference of the lens, are provided with beautif ully-distinct, 

 oval nuclei, with one or two nucleoli. These become smaller 

 as we pass deeper into the substance of the lens, and gradually 

 disappear. 



The regular arrangement of the fibres of the lens makes 

 it possible to separate its substance into layers, which have 

 been compared by anatomists to the layers of an onion ; but 

 this separation is entirely artificial, and the number of ap- 

 parent layers depends upon the dexterity of the manipulator. 

 It is to be noted, however, that the external 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 peculiar organic nitrogenized 

 substance, very analogous to globuline, called crystalline, com- 

 bined with various inorganic salts. One of the peculiar con- 

 stituents of this body is cholesterine. In an examination of 

 four fresh crystalline lenses of the ox, we found cholesterine, 

 in the proportion of 0*907 of a part per IjOOO. 1 In some 

 cases of cataract, cholesterine exists in the lens in a crystal- 

 line form ; but, under normal conditions, it is united with the 

 other constituents. 



Suspensory Ligament of the Lens (Zone of Zinri). When 

 we come to the description of the vitreous humor, we shall 

 see that it occupies about the posterior two-thirds of the 

 globe, and is enveloped in a delicate capsule, called the hya- 

 loid membrane. In the region of the ora serrata of the 

 retina, this membrane divides into two layers. The posterior 

 layer lines the depression in the vitreous humor into which the 

 lens is received. The anterior layer passes forward toward 

 the lens, and divides into two secondary layers, one of which 



1 FLINT, JR., Experimental Researches into a New Excretory Function of the 

 Liver. American Journal of the Medical Sciences, Philadelphia, 1862, New 

 Series, vol. xliv., p. 313 ; and, Recherches experimentales, etc., Paris, 1868, p. 18. 

 135 



