SENSE OF SIGHT. 



545 



rent branches of the long and the anterior ciliary. Its nervous 

 supply is the long and short ciliary nerves. 



Ciliary Processes (Fig. 323). The vascular layer of the choroid 

 with the lamina vitrea is arranged anteriorly in folds the ciliary 

 processes. These fit into corresponding folds of the suspensory 

 ligament of the crystalline lens. Their number varies from sixty 

 to eighty ; some being about 0.25 cm. in length, others shorter. In 

 structure they are like the choroid, except that their blood-vessels 

 are larger and are longitudinally arranged. On their posterior 

 surface are pigment-cells, as there are also in the processes them- 

 selves. 



Iris. This is a muscular and vascular structure in front of the 

 crystalline lens and behind the cornea. In its center is a circular 

 opening the pupil. Its structure is not unlike that of the 

 choroid, and on its anterior surface are pigment-cells, the color of 



FIG. 324. Crystalline lens and suspensory ligament or zonula : 1, lens ; 2, poste- 

 rior, and 3, anterior portion of zonula ; 4, its insertion into the pre-equatorial region. 

 The black rays are lines of pigment torn from the ciliary processes, and belong in 

 reality to the ciliary portion of the retina (Testut). 



whose pigment differs in different individuals. Its posterior sur- 

 face is covered with a layer of pigmented epithelial cells, the uvea, 

 which is continuous with those of the pars ciliaris retinae. 



The iris is composed of four layers : (1) Most anteriorly is a 

 layer of cells which is continuous with the epithelium of Desce- 

 met's membrane, and in these there is pigment. (2) The stroma ; 

 this consists of fibrous tissue, the fibers of which at the margin of 

 the pupil are circular, elsewhere, and for the most part, radiating. 

 Among these fibers are branched cells, containing pigment in 

 persons whose eyes are dark, while in light eyes the pigrrient is 

 absent. (3) A muscular layer consisting of the sphincter pupillce, 

 which is composed of involuntary fibers circularly arranged 

 around the pupil, and having a width of about 0.08 cm., and of 

 the dilator pupillce, composed of fibers arranged in a radiating 

 direction. (4) The pigmentary layer on the posterior surface of the 



35 



