THE SENSE OF VISION 603 



the cornea. On its inner surface there is a layer, of brown-black 

 pigment cells (the lamina fusca). The solera is connected by loose 

 connective tissue to the structures internal to it the ciliary body 

 and the choroid the space thus formed being known as the supra- 

 choroidal space (Fig. 345). 



The Choroid is the vascular coat for the posterior part of the eye. 

 It is connected with the ciliary body and the iris, and, together with 

 them, constitutes the vascular tract, or uvea, of the eye. Lying between 

 the sclera and the retina, the function of the choroid in to nourish 

 these structures, particularly the retina. Its pigment also absorbs 

 the light which passes through the retina. The choroid consists mainly 

 of networks of bloodvessels held together by a stroma containing 

 branched pigment cells. There is an outer layer of larger blood- 

 vessels, and an inner close network of wide capillaries. Next to the 

 xetina is a homogeneous elastic membrane, which may be 2 ^ thick. 

 A similar elastic membrane lies at the back of the cornea, and covers 

 the iris and ciliary processes. The fluid within the eyeball is contained 

 by this membrane, and it is probably of great 'importance in the 

 maintenance of the intra-ocular pressure. 



The Ciliary Body lies just behind the corneo-scleial junction, 

 being continuous with the choroid behind and with the iris in front, 

 and consists of two portions an outer muscular portion, the ciliary 

 muscle, and an inner non-muscular portion. The latter is divided 

 into two parts the pars plana and the pars plicata. 



The Ciliary Muscle is composed of smooth muscle, and also consists 

 of an outer portion and an inner portion. The fibres of the outer 

 portion (Briicke's muscle) run in a meridional and radial direction. 

 They arise from the portion of the cribriform ligament derived from 

 the cornea, and pass backwards to be inserted in part into the choroid, 

 in part into the suspensorj- ligament of the lens. 



The inner portion consists of circular fibres (Miiller's muscle). 

 It arises indirectly by interstitial tissue from the internal fibres of 

 the cribriform ligament, and forms a sphincter round the margin 

 of the leii. 



The Pars Plana is the posterior smooth portion of the ciliary body. 



The Pars Plicata is the anterior inner portion of the ciliary body, 

 so called because it is thrown into many folds the ciliary processes, 

 about seventy in number. Lying in the connective tissue of these 

 processes are networks of wide capillary tufts. Each "process arises 

 from a base of connective tissue continuous with the stroma of the 

 iris, and each is covered by columnar epithelium, within which is 

 a set of pigment cells. Between the processes lie the interciliary 

 grooves, lined by pigmented cubical cells, and continuous with the 

 radial furrows on the back of the iris. The sensory nerve supply of 

 the ciliary body comes from the ophthalmic division of the fifth nerve. 

 The ciliary muscle is supplied by the inferior division of the third nerve. 

 The long posterior ciliary arteries supply the ciliary body with blood . 



