228 THE NERVOUS SYSTEM. 



The ciliary body is a thickening of the choroid anteriorly, 

 at its junction with the cornea, sclerotic, and iris. Its sub- 

 stance is similar to that of the choroidal stroma, consisting of 

 vessels imbedded in connective tissue ; the choriocapillary 

 layer is wanting, the capillaries being more generally dis- 

 tributed. 



Its posterior surface is thrown up into radiating processes, 

 the ciliary processes, increasing in height toward the iris, at 

 the periphery of which they abruptly terminate. The vitreous 

 membrane is continued over the surface of these processes. 



Upon the posterior or inner surface of this membrane rests 

 a layer of pigmented epithelium, and then a single layer of 

 columnar epithelium ; these two layers are an anterior con- 

 tinuation of the retina (pars ciliaris retince). 



In the substance of the ciliary body is the ciliary muscle, 

 fasciculi of involuntary muscle arising near the corneo- 

 sclerotic junction and extending thence radially or meridion- 

 ally outward and backward, together with some circular 

 fasciculi. 



The ciliary body at the margin of the iris is united to the 

 corneo-sclerotic junction by fibrous processes, the ligamentum 

 pectinatum, the interstices of which form the lymph-spaces of 

 Fontana. 



The iris is attached by its peripheral margin to the ciliary 

 body at the corneo-sclerotic junction. It consists of six layers : 

 from before backward, endothelium, anterior boundary layer, 

 stroma, posterior boundary layer, pigment-layer, and limit- 

 ing membrane. 



The endothelium covering the anterior surface of the iris is 

 continuous with that on the posterior surface of the cornea. 



The anterior and posterior boundary layers and stroma of 

 the iris are continuations of choroidal tissue. 



The anterior boundary layer is a loose connective tissue 

 containing lymphoid cells ; it merges into the stroma. 



The stroma, or main portion of the iris consists chiefly of 

 radiating bloodvessels and circular and radiating fasciculi of 

 involuntary muscle imbedded in connective tissue. The con- 

 nective-tissue cells of the stroma and anterior boundary layer 

 contain pigment in varying amount, to which the color of 

 the iris is partly due. 



