55° 



DISTRIBUTION OF VESSELS 



[sect. 225. 



Fig. 222. 



orange, or brownish colour ; the regular pigment granules of the 

 proper pigment of the eye never being found here. 



The vessels of the choroid and iris are extremely numerous, and 

 present different conditions in the several parts. The choroid 

 receives its blood from the art. ciliares posteriores breves, about 

 twenty small vessels, which penetrate the sclerotic at the posterior 

 circumference of the eye-ball, at a variable distance from the optic 

 nerve, and then run forwards, dividing dichotomously in the mid- 

 dle or vascular layer of it, where they divide into three kinds of 

 branches : 1, an external series, which attain a certain fineness by 

 continued division, and theu pass directly into the venue vorticosce ; 

 2, an internal set, which pass into a capillary network immediately 

 beneath the pigment of the so-called membrana chorio-capillaris ; 



and, 3, an anterior series, which are continued 

 into the corpus ciliare and the iris. The 

 above-mentioned capillary network of the in- 

 nermost layer of the choroid, which lies on the 

 inner side of the tapetum in animals which 

 possess this structure, may be readily demon- 

 strated as a special membrane ; indeed it may 

 be partially shown even in man, in injected 

 and fresh preparations, and it forms one of the 

 densest and most beautiful plexuses ever met 

 with, for the meshes between vessels of croo^/", 

 themselves measure only o , o02" / to o - o05"', and 

 the capillaries proceed in a stellate manner 

 from the larger vessels. As already men- 

 tioned, this network reaches only as far as to 

 the or a serrata, where it gives place to some- 

 what coarser vascular convolutions with vessels 

 0004'" in diameter, derived from the anterior 

 branches of the ciliares posticw breves; these 

 form the processus ciliares, and are so thick, 

 that besides the vessels and a more homogene- 

 ous envelope supporting the ciliary processes, 

 no other tissue appears to be present in them. 

 The blocd is returned from these different re- 

 gions (and from the ciliary muscle, which like- 

 wise receives some twigs from the above- 

 mentioned arteries) , chiefly by the vena vorticosce, 

 which lie upon the arteries, two above and two below (sometimes 



Vessels of the choroid 

 and iris of a child, after 

 Arnold, seen from within, 

 and magnified 10 times. 

 a. capillary network of the 

 posterior section of the 

 choroid, terminating at the 

 ora serrata, b ; c. arteries 

 of the corona ciliaris, sup- 

 plying the ciliary processes 

 d, and partly proceeding 

 to e, the iris ; /. capillary 

 network of the inner sur- 

 face of the pupillary horder 

 of the iris. 



