CHORIOID. 



367 



ing the vessels. A thin inner layer of blood vessels, the lamina choriocapil- 

 laris, consists of a very close network of wide capillaries. The choriocapil- 

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

 structureless elastic lamella which may be 2 /z 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. 



Between the vascular lamina and the choriocapillaris there is a boundary 

 layer of fine elastic network generally without pigment. Here in ruminants 

 and horses there are many wavy bundles of connective tissue which give to the 

 eyes of those animals a metallic luster. Such a layer is known as the tapetum 

 jibrosum. The similarly iridescent tapetum cellulosum of the carnivora is 

 formed of several lavers of flat cells which contain numerous fine crvstals. 



X ^ 



'>;{ 



* 



Cross and longitudinal 

 sections of bundles 

 of scleral fibers. 



Lamina supra- 



chorioidea. 



Lamina vasculosa. 



Boundary zone. 



Choriocapillaris. 



: Basal membrane. 

 Pigment layer of the 

 retina. 



FIG. 419. VERTICAL SECTION THROUGH A PART OF THE HUMAN SCLERA AND THE ENTIRE THICKNESS 



OF THE CHORIOID. X 100. 

 g, Large vessels; p, pigment cells; c, cross sections of capillaries. 



The ciliary body encircles the eye as a muscular band, attached to the 

 inner surface of which there are from 70 to 80 meridional folds, the ciliary 

 processes (Fig. 410). The equator of the eye is vertical, like that of the 

 lens, and the meridians are antero-posterior. The processes begin low at 

 the ora serrata and rise gradually to a height of i mm., terminating abruptly 

 near the border of the lens. Each process consists of fibrillar connective 

 tissue containing numerous elastic fibers and blood vessels, and is bounded 

 toward the pars ciliaris retinae by a continuation of the lamina basalis 

 which forms intersecting folds. The ciliary processes, which are com- 

 pressible, may serve to prevent the increase of intraocular pressure during 

 the contraction of the ciliary muscle. The ciliary muscle is a band of 



