THE EYE, 241 



The inner vascular layer, called the chorio-capil- 

 laris, follows next, and consists almost entirely of a 

 very dense network of broad capillary blood-vessels. 

 Finally, the choroid is limited within, by an ex- 

 tremely delicate, finely striated membrane, called 

 the lamina vitrea, or membrane of Bruch. 



THE IRIS. 



The iris is a thin connective-tissue membrane, 

 pierced near the centre by an opening, the pupil, and 

 joined at the periphery to the ligament um pectin- 

 atum and the ciliary body. The bulk of the iris, 

 the substantiq propria, consists of delicate interlacing 

 connective-tissue fibres, among which are numerous 

 variously shaped, often branching pigmented and 

 unpigmented cells. 



It contains numerous blood-vessels which are 

 characterized by an extraordinary thickness of the 

 walls. Near the pupillary margin lies a circular 

 band of smooth muscle-cells sphincter pupillcE 

 while radiating bands of similar cells passing from 

 the periphery toward the pupil dilator pupillce 

 are found in certain animals, but not in man. The 

 anterior surface is covered by a layer of endothelial 

 cells, while the posterior surface is covered by an ir- 

 regular thicker layer of polyhedral cells, which are 

 densely crowded with pigment, and constitute the 



so-called uvea. 

 16 



