452 



HISTOLOGY 



elastic capsule, 6.5-25 n thick in front and 2-7 ju thick behind, which is 

 apparently derived from the lens itself. Within the capsule the anterior 

 surface of the lens is formed by the lens epithelium, a single layer of cells 

 2.5 M thick at the pole, but becoming taller toward the equator. There 

 they are continuous with the elongated lens fibers of the posterior layer, 

 which collectively are called the substantia lentis. 



Originally the fibers multiply throughout the lens, but in later stages 

 the formation of new fibers, as indicated by the presence of mitotic figures, 

 is limited to the region of transition between the lens epithelium and 

 the mass of lens fibers (Figs. 451,. E, and 460). When first formed the 

 fibers are short, but they increase in length and become six-sided prisms, 

 somewhat enlarged at one or both ends. The first fibers extend from one 

 surface of the lens to the other. Later these become buried in by the new 



FIG. 459. LENS FIBERS OF A NEW-BORN INFANT. 



A, Isolated lens fibers; three with smooth and one 

 with dentate borders. X 240. B, Human 

 lens fibers cut transversely; c, section 

 through club-shaped ends. X 560. 



IG. 460. CAPSULE AND EPITHELIUM OF A LENS OF 

 ADULT MAN. 



C, Tangential section. D. Meridional section across 

 the equator of the lens; I, capsule; 2, epithelium; 

 3, lens fibers. X 240. 



fibers formed at the periphery, and thus they constitute the nucelus of the 

 lens. This is a dense mass of somewhat shrunken fibers, which have lost 

 their nuclei and have acquired wavy or notched margins (Fig. 459). 

 The outer fibers of the cortical substance are softer. They have smooth 

 borders, and nuclei which are chiefly in the equatorial plane. Their proto- 

 plasm is transformed into a clear fluid substance, said to be chiefly a 

 globulin. The fibers are united to one another by a small amount of 

 cement substance, which is more abundant at the poles, at each of which it 

 forms a "lens star," usually with nine rays. 



When the fibers formed at the periphery of the original nucleus elongate so as to 

 cover it in, they do not extend from one pole to the other. Those that reach the ante- 

 rior pole fall short of the posterior pole, terminating along a horizontal suture of 

 cement substance; and conversely those that reach the posterior pole terminate 

 anteriorly along a linear vertical suture. As the lens becomes larger, the linear sutures 

 at either pole are replaced by tri-radiate or Y-shaped stars, one of which is inverted. 



