BLOOD-VESSELS OF THE EYEBALL. 



737 



(fig. 518, a, a). They terminate in the vascular network of the chorio-capillaris (m), which 



reaches as far as the ora serrata. 2. The long posterior ciliary ; one of these lies on the nasal 



and the other on the temporal side, and they run (6) to the ciliary part of the choroid, where 



they divide dichotomously, and penetrate 



into the iris, where they help to form the 



circulus arteriosus iridis major [p). 3. The 



anterior ciliary (c), which arise from the 



muscular branches, perforate the sclerotic 



anteriorly, and give branches to the ciliary 



part of the choroid and to the iris. About 



twelve branches run backwards (p) from 



them to the chorio-capillaris. 



Veins. 1. The anterior ciliary veins (c) 

 receive the blood from the anterior part of 

 the uvea and carry it outwards. These 

 branches are connected with Schlemm's canal 

 and Leber's venous plexus. They do not 

 receive any blood from the iris. 2. The 

 venous plexus of the ciliary processes (r) 

 receives the blood from the iris (q), and 

 passes backwards to the choroidal veins. 

 3. The large vasa vorticosa Stenonis (h) 

 perforate the sclerotic behind the equator 

 of the bulb. 



The inner margin of the iris rests upon 

 the anterior surface of the lens ; the poste- 

 rior chamber is small in adults, and in the 

 new-born child it may be said scarcely to 

 exist it is so small. When.Berlin blue is 

 injected into the anterior chamber of the 

 eye, it generally passes into the anterior 

 ciliary veins (Schivalbe). Even in living 

 animals, carmin also behaves in a similar 

 manner (Heisrath) ; hence, these observers 

 conclude that there is a direct communica- 

 tion between the veins and the aqueous 2^ J " 

 chamber, as these substances do not diffuse -p- f-,g 

 through membranes. -,.,-, , ' - -i ,. , 



Internal to the choroid, lies the single Diagram of the blood-vessels of. the eye(honzontal 

 layer of hexagonal cells (0*0135 to 0*02 

 mm. in breadth) filled with crystalline pig- 

 ment. This layer really belongs to the 

 retina. It consists of a single layer of cells 



as far as the ora serrata it is continued on 

 to the ciliary processes and the posterior 

 surface of the iris, where it forms several 

 layers (fig. 514, x). In albinos it is devoid 

 of pigment ; on the other hand, the upper- 

 most cells, which lie on the ridges of the 

 ciliary processes, are always devoid of pig- 

 ment. [The processes of these cells vary in 

 length with the nature and kind of light 

 acting on the retina ( 398).] 



The retina externally is in contact with 

 the layer of hexagonal pigment-cells (Pi), 

 which in its development and functions 

 really belongs to the retina. The cells are 

 not flat, but they send pigmented processes 

 into the space between the ends of the rods. 



view, veins black, arteries light, with a double 

 contour), a, a, short posterior ciliary ; b, long 

 posterior ciliary ; c, c', anterior ciliary artery and 

 vein ; d, d' } artery and vein of the conjunctiva ; 

 e, e', central artery and vein of retina ; /, blood- 

 vessels of the inner, and g, of the outer optic 

 sheath ; h, vorticose vein ; i, posterior short cili- 

 ary vein confined to the sclerotic ; k, branch of 

 the posterior short ciliary artery to the optic 

 nerve ; I, anastomosis of the choroidal vessels 

 with those of the optic ; m, chorio-capillaris ; n, 

 episcleral branches ; o, recurrent choroidal artery ; 

 p, great circular artery of iris (transverse section); 

 q, blood-vessels of the iris ; r, ciliary process ; s, 

 branch of a vorticose vein from the ciliary muscle ; 

 t, branch of the anterior ciliary vein to the ciliary 

 muscle ; u, circular vein ; v, marginal loops of 

 vessels on the cornea ; w, anterior artery and vein 

 of the conjunctiva. 



In some animals (rabbit) the cells contain fatty 

 granules and other substances. The cells are larger and darker at the orra serrata (Kilhne). 

 The retina is composed of the following layers, proceeding from without inwards : 



[1. Layer of pigment-cells. 



2. Eods and cones. 



3. External limiting membrane. 



4. Outer nuclear layer. 



5. Outer molecular (granular or 



ternuclear) layer. 



10. 



Inner nuclear layer. 



Inner molecular (granular) layer. 



Layer of nerve-cells (ganglionic) 



layer. 

 Layer of nerve-fibres. 

 Internal limiting membrane."] 

 3 A 



