CHOROID IRIS. 



619 



between corresponding foldings of the suspensory ligament of the lens, thus 

 establishing a communication between the choroid and inner tunic of the eye. 

 They are arranged in a circle, behind the iris, round the margin of the lens. 

 They vary in number between sixty and eighty, lie side by side, and may be 

 divided into large and small ; the latter, consisting of about one-third of the entire 

 number, are situated in the spaces between the former, but without regular alter- 

 nation. The larger processes are each about one-tenth of an inch in length, and 



Fig. 306. The Arteries of the Choroid and Iris. 

 The Sclerotic has beeii mostly removed. (Enlarged.) 



Short 

 Ciliary W 



hemispherical in shape, their periphery being attached to the ciliary ligament, and 

 continuous with the middle and inner layers of the choroid ; the opposite margin 

 is free, and rests upon the circumference of the lens. Their anterior surface is 

 turned towards the back of the iris, with the circumference of which it is con- 

 tinuous. The posterior surface is closely connected with the suspensory ligament 

 of the lens. 



Structure. The ciliary processes are similar in structure to the choroid ; the 

 vessels are larger, having chiefly a longitudinal direction. Externally they are 

 covered with several layers of pigment cells ; the component cells are small, 

 rounded, and full of pigment granules. 



The IRIS (iris, a rainbow) has received its name from the varied color it pre- 

 sents in different individuals. It is a thin circular-shaped, contractile curtain, 

 suspended in the aqueous humor behind the cornea, and in front of the lens, 

 being perforated at the nasal side of its centre by a circular aperture, the pupil, 

 for the transmission of light. By its circumference it is intimately connected 

 with the choroid ; externally to this is the ciliary ligament, by which it is con- 

 nected to the sclerotic and cornea; its inner edge forms the margin of the pupil ; 

 its surfaces are flattened, and look forwards and backwards, the anterior surface 

 towards the cornea, the posterior towards the ciliary processes and lens. The 

 anterior surface is variously colored in different individuals, and marked by lines 

 which converge towards the pupil. The posterior surface is of a deep purple 

 tint, from being covered by dark pigment; it is hence named uvea, from its 

 resemblance in color to a ripe grape. 



Structure. The iris is composed of a fibrous stroma, muscular fibres, and pig- 

 ment cells. 



The fibrous stroma consists of fine, delicate bundles of fibrous tissue, which have 

 a circular direction at the circumference; but the chief mass radiate towards 

 the pupil. They form, by their interlacement, a delicate mesh, in which the pig- 

 ment cells, vessels, and nerves are contained. 



