THE CRYSTALLINE LENS. 467 



F. THE VITREOUS BODY. 



The vitreous body is a tissue which consists almost entirely of 

 fluid, containing very few fixed cellular elements and only a small 

 number of leucocytes, which are found more particularly in its outer- 

 most portion. Thin structureless lamellae and fibers occur through- 

 out the entire vitreous body, with the exception of the hyaloid canal. 

 These fibrils form an interlacing network with wide meshes. They 

 differ chemically from both the white fibrous tissue and yellow elastic 

 fibers, resembling in some respects cuticular formations (von Ebner). 

 These are particularly numerous at the periphery and especially in 

 the region of the ciliary body. Toward the surface the fibrils are 

 more densely arranged, forming the hyaloid membrane of the vit- 

 reous body, separating the latter from the retina. This membrane 

 is somewhat thicker in the region of its close attachment around the 

 physiologic excavation of the optic nerve and to the internal limiting 

 membrane of the retina in the ciliary region. In the latter region 

 the hyaloid membrane is in close relation with the epithelium of the 

 pars ciliaris retinae. It does not, however, penetrate into and between 

 the ciliary processes, but extends like a bridge over the furrows be- 

 tween them. This arrangement gives rise to spaces, the recessus cam- 

 erce posterioris, which form a division of the posterior chamber, and 

 are inclosed between the hyaloid membrane, the ciliary processes, 

 the suspensory ligament of the lens, and the lens itself; these spaces 

 are filled with aqueous humor. In the region of the ciliary pro- 

 cesses the hyaloid membrane is closely associated with numerous 

 fibers, which diverge fan-like toward the lens and become blended 

 with the outer lamella of the lens-capsule. These fibers appear to 

 arise from the epithelium of the pars ciliaris retinae, and may be 

 regarded as cuticular formations. Those coming from the free ends 

 of the ciliary processes become attached along the equator of the lens 

 and to the adjacent posterior portion of the lens-capsule. On the 

 other hand, the fibers originating between the ciliary processes attach 

 themselves to the anterior surface of the lens-capsule in the imme- 

 diate vicinity of the equator. Together these fibers constitute the 

 zonula ciliaris ', zonule of Zinn, or the suspensory ligament of the lens. 

 Between these fibers of the zonula and the lens itself there is, conse- 

 quently, a circular canal divided by septa, the canal of Petit, which 

 communicates by openings with the anterior chamber. 



G. THE CRYSTALLINE LENS. 



As we have already seen, the crystalline lens originates as an 

 ectodermic invagination, which then frees itself from the remaining 

 ectoderm in the shape of a vesicle and becomes transformed into 

 the finished lens. In this process the cells of the inner wall of the 

 vesicle become the lens-fibers, while those of the outer portion re- 



