VESSELS OF THE RETINA. 



55 



lumen like true tubular glands (E. T. Collins). The function of these ciliary glands 

 is not certainly known, but they are believed to take part in the secretion of the 

 aqueous humour. 



Vessels of the Retina. A single artery (arteria emir alls retina) passes 

 between the bundles of fibres of the optic nerve to the inner surface of the retina 

 at the middle of the papilla optici (fig. 64). It enters the nerve about 

 15 20 mm. from the globe of the eye, being accompanied by the corresponding 

 vein and giving off small branches to supply the central part of the nerve. 

 Emerging at the papilla oculi the vessels divide into branches (fig. 63), usually 

 two, one above, the other below (superior and inferior papillary branches), each of 

 these again almost immediately dividing into two branches which arch out towards 



nasal 



temporal 



Fig. 63. RETINA AS SEEN WITH THE OPHTHALMOSOOPE. (Jaeger.) 

 a,a, branches of central artery ; v,v., branches of central vein ; /, fovea. 



the sides (superior and inferior nasal and temporal branches) the outer ones are 

 somewhat the larger, and as they bend round the macula lutea they send numerous 

 fine branches into it which end, a short distance from the centre of the fovea, in 

 capillary loops. The macula is also supplied by small vessels which pass directly 

 to it from the papilla. The middle of the fovea centralis has no blood-vessels. The 

 main branches of the vessels pass forwards in the nerve-fibre and ganglionic layers, 

 dividing dichotomously as they proceed, and giving off fine offsets to the substance 

 of the retina, where they form two capillary networks, the one in the nerve- and 

 ganglionic layer, the other in the inner nuclear layer. The capillaries of the former 

 are mainly connected with the arteries, and those of the latter with the veins, the 

 communication between the two networks being effected by vertically and obliquely 

 coursing capillaries which traverse the inner molecular layer. No vessels penetrate 

 the outer molecular layer (His, Hesse), so that the outer retinal layers are entirely 

 destitute of blood-vessels. The retinal arteries have no anastomoses, thus resembling 

 those of the grey matter of the brain. 



The vascular system of the retina is nowhere in direct communication with the 

 choroidal vessels. Near the entrance of the optic nerve, however, it comes into 

 communication with some offsets from the posterior ciliary in the sclerotic coat, and 

 the choroidal vessels also send branches to join the long-meshed network in the optic 



