THE CHOROID COAT. 717 



authors), and by vessels and nerves. The inner surface, which is smooth, is 

 lined by a continuous layer of pigmentary cells. 



The ciliary processes, about eighty-five in number, are arranged radiately 

 in a circle. They consist of larger and smaller folds, without regular alter- 

 nation, and the small folds number about one-third of the large. Each of 

 the larger folds, measuring aboub -j^th of an inch in length and 4 ^th in 

 depth, forms a rounded projection at its inner end, which is free from the 



Fig. 463. CILIA.RY PROCESSES AS SEEN Fig. 463. 



FROM BEHIND. f 



1, posterior surface of the iris, with the 

 sphincter muscle of the pupil ; 2, anterior 

 part of the choroid coat ; 3, one of the 

 ciliary processes, of which about seventy are 

 represented. 



pigment which invests the rest of the 

 structure ; but externally they become 

 gradually narrower, and disappear in 

 the choroid coat : the smaller pro- 

 cesses are only half as deep as the 

 others. At and near their internal or 

 anterior extremities the processes are 

 connected by lateral loop-like projec- 

 tions, and are separated from the iris by pigment. The plications of the 

 ciliary processes fit into corresponding plications of the suspensory ligament 

 of the lens. 



STRUCTURE. From a difference in the fineness of its constituent blood- 

 vessels, the choroidal coat resolves itself into two strata, inner and outer; 

 the latter containing the larger branches, and the former the capillary 

 ramifications. 



In the outer part of the coat are situated the branches of the vessels. 

 The arteries are large, and are directed forwards before they bend down- 

 wards to end on the inner surface ; whilst the veins (vasa vorticosa) are 

 disposed in curves as they converge to four of five principal trunks issuing 

 from the eyeball. In the intervals between those vessels are lodged elongated 

 and star-shaped pigment cells with very fine offsets, which intercommunicate 

 and form a network or stroma. Towards the inner part of the tunic, this 

 network passes gradually into a web without pigment : it resembles elastic 

 tissue in its chemical and physical properties. 



The inner part of the choroid coat (tunica Ruyschiana s. chorio-capillaris) 

 is formed by the capillaries of the choroklal vessels. From the ends of the 

 large arteries the capillaries radiate in a star-like manner, and form meshes 

 which are more delicate and smaller than in any other texture, and are 

 finer at the back than the front of the ball. This fine network reaches as 

 far forwards as about |th of an inch from the cornea, or opposite to the 

 ending of the expansion of the optic nerve, where its meshes become larger, 

 and join those of the ciliary processes. 



On the inner surface of the tunica Ruyschiana may be detected, according 

 to various authors, a structureless transparent membrane, the membrane of 

 Bruch, underlying the pigmentary layer. 



The ciliary processes have the same structure as the choroid, of which they 

 are a part ; but the capillary plexus of the vessels, less fine, has meehes 



