Structure.The ciliary processes (Figs. 876,877) are similar in structure to the choroid, but the vessels are larger, and have chiefly a longitudinal direction. Their posterior surfaces are covered by a bilaminar layer of black pigment cells, which is continued forward from the retina, and is named the pars ciliaris retinæ. In the stroma of the ciliary processes there are also stellate pigment cells, but these are not so numerous as in the choroid itself.
According to Henderson the aqueous humor is a secretion formed by the active intervention of the epithelial cells lining the apices of the ciliary processes.1
The Ciliaris muscle (m. ciliaris; Bowmans muscle) consists of unstriped fibers: it forms a grayish, semitransparent, circular band, about 3 mm. broad, on the outer surface of the fore-part of the choroid. It is thickest in front, and consists of two sets of fibers, meridional and circular. The meridional fibers, much the more numerous, arise from the posterior margin of the scleral spur (page 1007); they run backward, and are attached to the ciliary processes and orbiculus ciliaris. One bundle, according to Waldeyer, is inserted into the sclera. The circular fibers are internal to the meridional ones, and in a meridional section appear as a triangular zone behind the filtration angle and close to the circumference of the iris. They are well-developed in hypermetropic, but are rudimentary or absent in myopic eyes. The Ciliaris muscle is the chief agent in accommodation, i. e., in adjusting the eye to the vision of near objects. When it contracts it draws forward the ciliary processes, relaxes the suspensory ligament of the lens, and thus allows the lens to become more convex.
FIG. 876 Vessels of the choroid, ciliary processes, adn iris of a child. (Arnold.) Magnified 10 times. a. Capillary net-work of the posterior part of the choroid, ending at b, the ora serrata. c. Arteries of the corona ciliaris, supplying the ciliary processes, d, and passing into the iris e. f. The capillary net-work close to the pupillary margin of the iris. (See enlarged image)