EYE 453 



Lens fibers starting near the center of one star end near the tips of the rays of the 

 other, and vice versa. When the stars become nine-rayed the arrangement of the 

 fibers is very intricate. Without crossing one another, and without any of them being 

 long enough to pass from pole to pole, they cover the lens with even layers. The 

 development of the stars is described by Rabl (Ueber den Bau und Entwicklung der 

 Linse, Leipzig, 1900). As a result of its structure the lens may be separated into con- 

 centric lamellae, but Rabl considers that the meridional segments, or "radial lamellae," 

 of which the lens contains about two thousand, are its essential subdivisions. 



VITREOUS BODY. 



The corpus vitreum consists of the fluid vitreous humor, together with 

 looser or denser strands of fibrous stroma which stretch across it in all 

 directions. Although it is difficult to recognize any definite arrangement 

 in the stroma, certain pathological cases suggest that it is distributed like 

 the septa of an orange. The cells of the vitreous body are round forms, 

 probably leucocytes, and stellate or spindle-shaped connective tissue 

 cells, sometimes degenerating and vacuolated, which invaded the vitreous 

 body with the blood vessels. The latter have atrophied and been resorbed, 

 except for occasional shreds and filaments. Such opacities, which occur 

 normally, are observed when looking at a bright light, and are frequently 

 troublesome to those beginning to use the microscope; because of their 

 erratic motion they are known to physiologists as musca volitantes. In 

 old age, in eyes otherwise normal, crystals may form in the vitreous 

 humor and float about, " falling like a shower to the bottom of the eye when 

 the eye is held still." Surrounding the vitreous body there is a very re- 

 sistant thick fibrous layer, which is continuous anteriorly with the hyaloid 

 membrane of the ciliary part of the retina. 



TUNICA VASCULOSA. 



Chorioid. Between the sclera and the chorioid there is a loose tissue 

 containing many elastic fibers and branched pigment cells, together with 

 flat non-pigmented cells. In separating the sclera from the chorioid, this 

 layer is divided into the lamina fusca of the sclera and the lamina supra- 

 chorioidea. Internal to the latter is the lamina vasculosa, which forms the 

 greater part of the chorioid. It contains many large blood vessels im- 

 bedded in a loose elastic connective tissue, some of its cells being branched 

 . and pigmented; others without pigment are flat and arranged in layers sur- 

 rounding the vessels. A thin inner layer of blood vessels, the lamina chorio- 

 capillaris, consists of a very close network of wide capillaries. The chorio- 

 capillaris is separated from the pigmented epithelium of the retina by a 

 structureless elastic lamella which may be 2 ^ thick. This lamina basalis 

 shows the imprint of the polygonal retinal cells on its inner surface, and is 

 associated with fine elastic networks toward the choriocapillaris. 



