VASCULAR SYSTEM OF THE RETINA. 319 



The arteria and vena centralis run in the axis of the optic 

 nerve, to the surface of the papilla, at which point, or some- 

 what earlier, they break up into their principal branches, the 

 vein usually dividing somewhat earlier than the artery. The 

 mode of branching is dichotomous. A main branch, both of 

 the artery and vein, runs upwards ; the others downwards, and 

 these again quickly subdivide and diverge at different angles 

 from one another. The veins pursue approxirnatively the same 

 direction as the arteries, at least in their larger branches, and 

 are usually of larger size. Numerous variations, within certain 

 limits, occur in different individuals. No large vessel ever runs 

 outwards towards the temple, and over the macula lutea, except 

 in extremely rare cases (Mauthner) ; all the larger vessels curve 

 round the yellow spot, to reach the peripheric portions of the 

 retina, and send small branches from all sides into the macula. 

 Similar small vessels pass to it also directly from the papilla. 

 These supply the macula, but all terminate at the border of the 

 fovea centralis by means of capillary loops, so that this last is 

 quite destitute of vessels. 



The capillary plexus of the retina is distinguished from that 

 of the choroid by its much wider meshes, the capillaries them- 

 selves are finer and very thin- walled. The mode of ramifica- 

 tion of the retinal vessels closely resembles that of the central 

 organs of the nervous system. According to His, peri vascular 

 lymph spaces surround the retinal vessels very similar to those 

 of the vessels of the brain and spinal cord. 



The larger branches of the central vessels all run in the 

 nerve-fibre layer of the retina, and become smaller in propor- 

 tion as they are situated more externally in the successive 

 layers of the retina. The smaller branches penetrate as far as 



vorticosa ; i, vense ciliares posteriores breves ; k t branch of the art. cil. 

 post. brev. to the optic nerve ; I, anastomoses of the choroidal vessels 

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

 branches ; o, arteria recurrens choroidalis ; p, circulus arteriosus iridis 

 major (transverse section) ; q, vessels of the iris ; r, of the ciliary pro- 

 cess ; s, branch to the vena vorticalis from the ciliary muscle ; t, branch 

 to the anterior ciliary vein, proceeding from the ciliary muscle ; u, 

 circulus venosus ; v, marginal loop-plexus of the cornea ; iv, arteria 

 et vena conjunctivalis anterior. 



