THE ANTERIOR CHAMBER 577 



are distributed in a plane parallel to the surface of the iris, and 

 within the inner (posterior) part of its fibrous stroma. They are 

 most abundant near the pupillary margin, and become progressively 

 thinner toward the base of the iris. Internally to the sphincter 

 muscle, arid in contact with the basement membrane of the internal 

 epithelium, is an incomplete layer, more distinct toward the ciliary 

 margin of the iris, which contains radially disposed smooth muscle 

 fibres, the dilator muscle of the iris. 



The stroma of the iris is exceedingly vascular, the arteries and 

 veins being meridionally disposed, the capillaries forming an irregu- 

 lar plexus. Near the pupillary margin the vessels form a rich 

 capillary anastomosis, the circulus minor. The entering arteries 

 likewise form a circulus major by anastomoses at the ciliary margin 

 of the iris. 



The internal epithelium (posterior epithelium, pigment epithe- 

 lium of the iris, pars iridis retince) resembles that of the ciliary 

 body or pars ciliaris retinae, with which it is continuous. The 

 innermost (superficial) layer of epithelial cells, in the iridal epithe- 

 lium, is deeply pigmented and somewhat flatter than in the ciliary 

 body. The pigmentation is so deep that in the adult iris it is 

 scarcely possible to distinguish the two epithelial layers. These 

 can, however, be readily seen in the fetal eye, and even in that of 

 the child. In albinos the pigment of the epithelium, as well as 

 that of the stroma, is very scanty, or may even be entirely absent. 



THE ANTERIOR CHAMBER is bounded in front by the pos- 

 terior (internal) surface of the cornea, and behind by the anterior 

 surface of the crystalline lens and the anterior (external) aspect of 

 the iris ; it contains the aqueous humor. Its anterior boundary is 

 convex, its posterior concave, and its circular margin is limited by 

 an area which is known as the irido-corneal angle. 



At this angle the epithelium is reflected from the posterior sur- 

 face of the cornea upon the anterior surface of the iris. The latter 

 portion of the epithelial layer is incomplete, since it presents nu- 

 merous openings which communicate with the lymphatic spaces 

 between the fibres of the ligamentum pectinatum and ciliary mus- 

 cle. These lymphatic recesses are the spaces of Fontana. 



The ligamentum pectinatum consists of fibres which arise from 

 the margin of Descemet's membrane, and pass backward and in- 

 ward, in a radial direction, to the fibrous stroma of the iris and 

 ciliary body. Viewed from the cavity of the anterior chamber the 

 fibres of this ligament, with the intervening spaces of Fontana, 

 38 



