666 THE EYE 



THE CRYSTALLINE LENS 



The crystalline lens with its suspensory ligament forms a sort of 

 diaphragm which separates the ocular cavity into two compartments, 

 of which the anterior is occupied by the aqueous humor, the posterior 

 by the vitreous humor. 



The lens is a biconvex transparent body having a somewhat greater 

 convexity on its posterior than on its anterior surface; its curvature 

 is greater at its margin than toward its center. It has a transverse 

 diameter of from 8 mm. to 9 mm., and an anteroposterior diameter of 

 from 3.5 mm. to 4 mm. according to the degree of accommodation. It 

 consists of a capsule, epithelium, and a substantia lentis. 



The capsule of the lens is a homogeneous membrane which covers 

 its entire surface and receives the attachment of the suspensory liga- 

 ment. It presents faint meridional striations and may sometimes be 

 separated into several lamellae' (Berger, 1893) ; this lamellation may be 

 purely artificial, but appears to be somewhat dependent upon the attach- 

 ment of the fibers of the suspensory ligament to the surface of the 

 lenticular capsule. 



The capsule is about twice as thick over the anterior as over the 

 posterior surface of the lens. On the former surface it is in relation 

 with the lenticular epithelium, but on the posterior surface the capsule 

 rests directly upon the substantia lentis. The anterior surface of the 

 capsule is in gentle contact with the free margin of the iris. 



The lenticular epithelium consists of a single layer of cells which 

 covers the entire anterior convexity of the lens, extending as far back as 

 its equator. The height of these cells varies with the age of the indi- 

 vidual. In fetal life they are distinctly columnar, in youth short colum- 

 nar or cuboidal, in adult life low cuboidal or flattened. Toward the mar- 

 gin of the lens the epithelial cells become progressively lengthened, and 

 at its equator are transformed directly into the fibers of the lenticular 

 substance. This definitive structure of the lens recalls its manner of 

 development from the original lens vesicle; the hollow vesicle becomes 

 solid by the elongation of the cells of the posterior wall. 



The substantia lentis is, therefore, the product of the epithelium 

 of the lens, whose cells become greatly elongated to form slender hexag- 

 onal prisms, known as the lens fibers. When it is first formed each 

 prism exhibits a nucleus which persists for some time, but gradually 

 disappears as in the process of growth the older fibers become farther 

 and farther removed from their source of nutrition, the lymph and the 



