CILIARY PROCESSES. 



685 



lar alternation. The larger processes are each about one-tenth of an inch in 

 length, and 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 circumstance of the lens. Their 



Fig. 371. The Arteries of the Choroid and Iris. The Sclerotic has been mostly removed. 



(Enlarged.) 



Short 

 Ciliary 4/ 



anterior surface is turned towards the back of the iris, with the circumference 

 of which it is continuous. 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 its various color 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 perfo- 

 rated 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 connected 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 

 pigment-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 pigment-cells, vessels, and nerves are contained. 



The muscular fibre is involuntary, and consists of circular and radiating fibres. 

 The circular fibres (sphincter of the pupil) surround the margin of the pupil on 

 the posterior surface of the iris, like a sphincter, forming a narrow band, about 

 one-thirtieth of an inch in width; those near the free margin being closely 

 aggregated; those more external somewhat separated, and forming less com- 

 plete circles. The radiating fibres (dilator of the pupil) converge from the 



