454 



HISTOLOGY 



Between the vascular lamina and the choriocapillaris, there is a boundary layer 

 consisting of a 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 fibrosum. 

 The similarly iridescent tapetum cellulosum of the carnivora is formed of several 

 layers of flat cells which contain numerous fine crystals. 



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. 452). 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 



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. 461. VERTICAL SECTION THROUGH A PART OF THE HUMAN SCLBRA AND THE ENTIRE THICKNESS OF 



THE CHORIOID. X 100. 



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



lamina basalis, which is thrown into intersecting folds. The ciliary proc- 

 esses, which are compressible, may serve to prevent the increase of intra- 

 ocular pressure during the contraction of the ciliary muscle; and the 

 fluid within the eye is derived from the vessels which they contain. The 

 ciliary muscle is a band of smooth muscle fibers about 3 mm. broad and 

 0.8 mm. thick anteriorly; it arises beneath the sinus venosus of the sclera 

 and tapers toward the ora serrata (Fig. 425). It consists of three sets 

 of fibers, the meridional, radial, and circular. The meridional fibers (Fig. 

 452, p. 443) are next to the sclera, grouped in numerous bundles with elastic 

 tissue intermingled. They extend to the smooth part of the chorioid, 

 and constitute the tensor chorioidea. The radial fibers are directed to- 



