THE IRIS 575 



muscle. Into the inner portion of the fibrous layer a vascular plexus 

 is continued from the vascular and capillary layers of the choroid ; 

 branches of the ciliary arteries turn forward between the bundles of 

 the ciliary muscle to communicate with this plexus. 



Appended to the inner surface of the fibrous layer are numer- 

 ous meridionally disposed folds of connective tissue which radiate 

 from the base or outer margin of the iris to the margin of the cho- 

 roid opposite the ora serrata. These are the ciliary processes. Their 

 inner or free surface is covered by the pigmented retinal epithe- 

 lium, and within these processes are contained the greater portion 

 of the pigmented connective tissue cells of the ciliary body. Each 

 fold is much deeper toward its axial margin and becomes progress- 

 ively diminished in height toward the choroid. 



The pigmented epithelial layer is here and there invaginated 

 into the fibrous tissue of the ciliary processes to form ampullate 

 recesses (the ciliary glands), which somewhat resemble true secret- 

 ing glands. These so-called glands have been supposed to be con- 

 cerned in the secretion of the aqueous humor. They are probably 

 not true secreting glands, but represent mere invaginations of the 

 epithelium. 



The ciliary epithelium (pars ciliaris retina, pigment layer of 

 the ciliary body) consists of a double layer of epithelial cells, con- 

 tinuous posteriorly with the retina, and in front with the pars iridis 

 retinae. The superficial (innermost) cells present a clear or slightly 

 granular cytoplasm with a centrally situated nucleus. Their cyto- 

 plasm is but slightly pigmented, and ofttimes is indistinctly rodded 

 or fibrillated. In shape, these cells are of the low columnar type, 

 but they become progressively flattened toward the iris, where they 

 are continuous with the pars iridis retinae. 



The cells of the deeper (outer or anterior) layer vary in height 

 from a low columnar at the ora serrata to a somewhat flattened cell 

 near the iridal margin. This cell layer is deeply pigmented, the 

 entire cytoplasm being filled with the dark brown pigment granules. 

 The nucleus, however, as in the pigmented cells of the choroid, con- 

 tains no pigment, and therefore, in unstained preparations, appears 

 under the microscope as a clear opening in the dark background 

 of pigmented cytoplasm. 



THE IRIS (Figs. 417 and 422). The iris forms an annular 

 curtain which projects from the anterior margin of the ciliary body 

 toward the axis of the eye. It presents a central circular opening, 

 the pupil, which lies in the visual axis. 



