SENSE OF SIGHT. 



555 



the fiber is seen to be a hexagonal prism. The superficial fibers 

 contain nuclei, giving to the external layer the name nucleated 

 layer. The fibers are developed from epithelium-cells. The 

 centers of the anterior and posterior surfaces are the poles, and 

 the margin of the lens, where these surfaces meet, is the equator. 

 During fetal life the lens is 

 nearly spherical, not very trans- 

 parent, and quite soft in consist- 

 ence ; in adult life its posterior 

 surface is more convex than the 

 anterior, and it is transparent. 

 Its consistence has already been 

 described. In old age its con- 

 vexity and transparency are 

 diminished and its density in- 

 creased. 



Capsule .of the Lens. This, 

 like the lens, is transparent ; it 

 is structureless and elastic. At 

 the front and the sides of the 

 capsule on its inner surface is 

 a layer of cubical epithelium, 

 the epithelium of the capsule. 

 These cells are elongated at the 

 margin of the lens and become 

 lens-fibers. This epithelium is 

 absent from the posterior sur- 

 face. The suspensory ligament 

 is attached to the capsule around 

 its circumference. Anteriorly 

 the capsule and the border of 

 the iris are in contact; at the 

 circumference they are slightly separated, the space thus left being 

 the posterior chamber. 



Suspensory Ligament. This is the anterior part of the hyaloid 

 membrane which divides into two layers at the pars ciliaris 

 retinae. Its anterior surface is arranged in folds, in the depressions 

 of which the ciliary processes lie. From these processes the liga- 

 ment passes to the capsule of the lens. Its function is to assist in 

 retaining the lens in position. 



Chemistry of the Eye. Cornea. An analysis of the cornea 

 shows that it consists of the following ingredients : Water, 75.8 

 per cent. ; collagen, 20.4 per cent. ; other organic matter, 2.8 per 

 cent. ; and ash, 1 per cent. 



Retina. This tunic has been analyzed in geese, with the fol- 

 lowing result : 



FIG. 332. Crystalline lens : A, longi- 

 tudinal fibers ; a, anterior capsule ; 6, 

 anterior epithelium; c, lens-fibers. B, 

 posterior surface view of anterior epithe- 

 lium (Leroy). 



