468 THE EYE. 



main as the anterior epithelium of the lens. The lens is surrounded 

 on all sides by the lens-capsule. 



The lens capsule is a homogeneous membrane, nearly twice as 

 thick on the anterior surface of the lens as on the posterior. Its 

 chemic reactions differ from those of connective tissue, and in this 

 respect it may be compared with the membranae propriae of 

 glands. In sections the lens capsule appears to possess a tangen- 

 tial striation ; under the influence of certain reagents, and under 

 proper preliminary treatment, lamellae may be detached from its 

 surface which are found to be directly connected with the fibers 

 of the suspensory ligament. 



The anterior epithelium consists, in the fetus, of columnar cells ; 

 in children, of cells approaching the cubic type ; and in the adult, of 

 decidedly flattened cells. Toward the equator of the lens, in the 

 so-called transitional zone, the cells increase in height and gradually 

 pass over into the lens fibers. 



The lens fibers are also derivatives of epithelial cells ; they are 

 long, flattened, hexagonal prisms, which extend through the entire 

 thickness of the lens. In the adult the lens may be differentiated 

 into a resistant peripheral and a softer axial substance. The sur- 

 faces of the fibers present irregularities, and it is with the help of 

 these serrations and a cement substance that the fibers are bound 

 together. Each fiber possesses one or more nuclei, which, although 

 they have no constant position, are usually found in the middle of 

 the. fibers situated near the lens-axis, and in th'e anterior third of 

 those at some distance from the axis. The course of the fibers in 

 the lens is extremely complicated. 



H. THE FETAL BLOOD-VESSELS OF THE EYE. 



In the eye of the embryo the vitreous body and the capsule of 

 the lens contain blood-vessels. The vessel which later becomes 

 the central artery of the retina passes through the space sub- 

 sequently occupied by the vitreous body as far as the posterior sur- 

 face of the lens (anterior hyaloid artery) and branches in the region 

 of the posterior and anterior lens-capsule. The anterior vascular 

 membrane of the lens capsule of the embryo is known as the 

 membrana capsulopupillaris, and that portion corresponding to the 

 pupil, as the membrana pupillaris. In the embryo numerous other 

 vessels arise at the papilla and extend over the surface of the 

 vitreous body close to the hyaloid membrane ; these are the pos- 

 terior hyaloid arteries. These vessels later disappear. In place of 

 the anterior hyaloid artery there remains in the vitreous humor a 

 transparent cylindric cord containing no fibers nor lamellae, as is the 

 case in the remaining portion of the vitreous body, and consisting 

 of a more fluid substance ; this is the hyaloid canal, or the canal of 

 Cloquet. 



