EYE 



455 



ward the center of the eye-ball. They form a middle layer of curving 

 fibers which blend with the meridional fibers externally. The circular 

 fibers, which vary in number in different individuals, form that part of the 

 ciliary muscle which is nearest to the equator of the lens. The contrac- 

 tion of these muscles affects 

 the shape of the lens, which is 

 attached to the adjacent tissue 

 by the zonula. 



The iris consists of its stroma 

 anteriorly, and the pars iridica 

 retina posteriorly, and is covered 

 by the mesenchymal epithelium 

 of the chambers of the eye. 

 The anterior epithelium is a 

 simple layer of flat polygonal 

 cells (sometimes called "endo- 

 thelium"). It rests upon a 

 loose network of stellate cells, 

 in part pigmented, resembling 

 the reticulum of a lymph gland. This is followed by the loose connec- 

 tive tissue of the stroma, likewise containing networks of stellate cells, 

 which in blue eyes are not pigmented. The very few elastic fibers are 

 limited to the posterior layers, where they are radially arranged in rela- 



Mesenchymal 

 epithelium. 



Loose connective 

 tissue. 



p 



FIG. 462. A, FROM A TEASED PREPARATION OF A HUMAN 

 CHORIOID. X 240. p, Pigment cells; e, elastic fibers; 

 k, nucleus of a flat non-pigmented cell; the cell body 

 is invisible. 



B, PORTION OK A HUMAN CHORIOCAPILLARIS AND THB 

 ADHERENT LAMINA BASALIS. X 240. c, Wide 

 capillaries, some of which contain (b) blood-corpus- 

 cles; e, lamina basalis, showing a fine lattice work." 



r/t 



Vascular layer. 



Spindle cell layer. 



JBi 



FIG. 463. VERTICAL SECTION OF THE PUPILLARY PORTION OF A HUMAN IRIS. X 100. About one-fifth 



of the entire width of the iris is shown. 



g, Blood vessel, with thick connective tissue sheath; m, sphincter pupilla muscle cut transversely; 



pupillary border of the iris. 



tion to the pupil. The stroma contains numerous radial blood ves- 

 sels with thick connective tissue coats, but (in man) without muscu- 

 lature or elastic fibers. In the vascular layer, toward the pupillary 

 border of the iris, there is a band of circular smooth muscle fibers, i 

 mm. deep; this is the sphincter pupilla. It is invested with many 



