THE EYE. 895 



behind than in front. Externally it is connected by a fine cellular web (membrana 

 /) with the inner surface of the sclerotic. Its inner surface is smooth and 

 lies in contact with the retina. 



Structure. The choroid consists mainly of a dense capillary plexus and of 

 small arteries and veins, carrying the blood to and returning it from this plexus. 

 On its external surface i. >'. the surface next the sclerotic is a thin membrane 

 of fine elastic fibres arranged in lamellae, which are covered with endothelium and 

 form spaces, which communicate by perforations in the sclerotic, through which 

 the vessels and nerves enter, with the capsule of Tenon. This layer is named the 

 lamina mprackoroidea, and is continuous with the lamina fusca of the sclerotic. 



Internal to this is the choroid proper, and, in consequence of the small arteries 

 and veins being arranged on the outer surface of the capillary network, it is cus- 

 tomary to describe this as consisting of two layers, the outermost composed of 

 small arteries and veins, with pigment-cells interspersed between them, and the 



FIG. 529. The veins of the choroid. (Enlarged.) 



inner consisting of a capillary plexus. The external layer consists, in part, of 

 the larger branches of the short ciliary arteries, which run forward between the 

 veins before they bend inward to terminate in the capillaries ; but is formed 

 principally of veins, which are named, from their arrangement, vence vorticosce. 

 Thev converge to four or five equidistant trunks, which pierce the sclerotic mid- 

 way between the margin of the cornea and the entrance of the optic nerve. Inter- 

 spersed between the vessels are lodged dark star-shaped pigment-cells, the fibrous 

 offsets from which, communicating with similar branchings from neighboring cells, 

 form a delicate network or stroma, which toward the inner surface of the choroid 

 loses its pigmentary character. The internal layer consists of an exceedingly fine 

 capillary plexus, formed by the short ciliary vessels, and is known as the tunica 

 Ruii*<:-liinna. The network is close, and finer at the hinder part of the choroid 

 than in front. About half an inch behind the cornea its meshes become larger, 

 and are continuous with those of the ciliary processes. On the inner surface of 

 this tunic is a very thin, structureless or, according to Kolliker, faintly fibrous 

 membrane, called the lamina vitrea ; it is closely connected with the stroma of the 

 choroid. and separates it from the pigmentary layer of the retina. 



The ciliary processes should now be examined. They may be exposed, either by detaching 

 the iris from its connection with the Ciliary muscle, or by making a transverse section of the 

 globe and examining them from behind. 



The ciliary processes are formed by the plaiting and folding inward of the 

 various layers of the choroid (i. e. the choroid proper and the lamina vitrea) at its 

 anterior margin, and are received between corresponding foldings of the suspensory 



