THE VASCULAR TUNIC 



743 



of the proper tissue of the ehorioid. It contains the larger blood-vessels, which 

 are supported by connective-tissue and elastic fibers. (3) The lamina chorio- 

 capillaris consists of an extremely rich network of capillaries embedded in an almost 

 homogeneous matrix. Between it and the lamina vasculosa is a layer of fibro- 

 elastic tissue, the tapetum fibrosum, which causes the metallic luster mentioned 

 above. (4) The lamina basalis is very thin and transparent. It is composed of 

 an inner homogeneous part and an outer elastic part. 



2. The ciliary body (Corpus ciliare), the middle part of the vascular coat, con- 

 nects the ehorioid with the peri]ihery of the iris. In meridional section it has the 

 form of a narrow triangle, the bas(^ of which is next to the iris. On its inner side 

 are the ciliary processes and on its outer side the ciliary muscle. It consists of 

 three parts — the ciliary ring, ciliary processes, and ciliary muscle. The ciliary 

 ring (( )rl)icularis ciliaris) is the posterior zone, which is distinguished from the ehor- 

 ioid mainly by its greater thickness 

 and the al)sence of the chorio-capil- 

 laris. Its inner face presents numer- 

 ous fine meridional ridges, by the 

 union of wiiich tiie ciliary j^rocesses 

 are formed. The ciliary processes 

 (Processus ciliares), more than a 

 hundred in number, form a circle 

 of radial folds which surround the 

 lens and furnish attachment to tlie 

 zonula ciliaris or suspensory liga- 

 ment of the latter. They are small 

 at their origin on the ciliary ring 

 and ])ecome much thicker and 

 higher toward their inner ends. 

 The width of the circle formed by 

 them is narrower at the inner side 

 than elsewhere. Their bases ex- 

 tend forward to the periphery of 

 the iris, and their inner ends are 

 close to the margin of the lens. 

 They bear numerous secondary 

 folds. Their inner surface is cov- 

 ered by a continuation of the 

 lamina basalis of the ehorioid, on 

 which there are two layers of epi- 

 thelial cells which constitute the 

 pars ciliaris retina^. They consist 



of a rich network of tortuous vessels supported in pigmented connective tissue. 

 The ciliary muscle (M. ciharis) (Figs. 552, 555, 559) constitutes the outer part of 

 the ciliary body, and lies between the sclera and the cihary processes. It forms 

 a circular band of unstriped muscle, the fibers of which are for the most part 

 directed meridionally. They arise from the inner surface of the sclera and from 

 the ligamentum pectinatum iridis close to the corneo-scleral junction, and run 

 backward along the sclera to be inserted into the ciliary processes and ring. 

 When the muscle contracts, it pulls the processes and ring forward, thus 

 slackening the ciliary zone or suspensory ligament of the lens, and allowhig 

 the latter to become' more convex. This is the mechanism of accommodation 

 for near objects. 



In man the muscle has the form of a prismatic ring which is triangular in meridional section, 

 the base being directed toward the periphery of the iris. 



Fig. 559. 



flaps. 



Vascular Tunic of Eyeball of Horse, Front 

 View. 

 The cornea is removed and the sclera is reflected in 

 1, Sclera; /', lamina fusca; 2, chorioidea; 2' , ciliary 

 veins; S, ciliary muscle; 4, iris; 5, o', granula iridis; 6, pujjil, 

 through which the lens' is visible. (After Ellenberger, in 

 Leisering's Atlas.) 



It consists chiefly of meridional fibers, 



