EXAMINATION OF THE EYEBALL 851 



the nerve-tmnk, iind tlu-n divides into branches which run in the inner layers of the 

 retina, and divide dicliotoniously as they radiate towards tlie equator. The smaller 

 branches lie more deeply in the retina, Imt none penetrate into the nerve-epithelium, 

 so that the fovea centralis is non-vascular. In the retina, the branches of the cen- 

 tral artery do not comnmnicate with any other arteries, Ijut while still in the oijtic 

 nerve fine communications take place between this artery and neighl)ouring vessels. 

 Thus (a) minute twigs from it, which hel]) to nourish tlie axial part of the nerve 

 communicate with those running in the septa derived from the pial sheath. Again,' 

 as the nerve passes through the sclerotic, it is surrounded by a vascular ring (circle 



Fig. 478.— DiAGR.VMJi.vnc Representation of the Blood-ve.ssei>s of the Eyeball. 



(Leber.) 



Arteries rerf; veiiis Wwe. 



Canal of Schlentm and con- 



nections with anterior 



ciliary vein 



Branch from ciliary body to 



anterior ciliary vein 



Cessels of ciliary processes 



Vein from iris and ciliory 

 body to vena rorticosa 



Branch from short posterior 

 ciliary artery to optic nerve 



Short posterior ciliary artery_ 



I'ena centralis retince 



Jfarffin al corneal plexus 



Ttnlerior conjunctival vein 



Cireulus iridis major 

 Posterior conjunctival vein 



Anterior ciliary vein 



Posterior conjunctival 



artery 

 A nierior ciliary artery 



Episcleral vein 

 Episcleral artery 



I'ena vorticosa 



Posterior long ciliary artery 

 Posterior short ciliary arteries 



Vessels of pial sheath of optic nerve 

 Vessels of dural sheath 



Arleria centralis retince 



of Haller), formed of fine branches derived from the short jnj.sterior ciliary arteries; 

 fine twigs ]jassing inwards from this ring to the optic nerve, join the vessels of the 

 pial sheath, and (b) an indirect communication is thus l)rought about between the 

 retinal and ciliary vessels. Finally, as the nerve passes througii the choroid, there 

 is (c) a direct connection between these two sets of vessels, the cajiillary network of 

 the optic nerve being here continuous with the chorio-ca))illaris. Not infre(|uently, 

 a branch from a short posterior ciliary artery ])ierces the ojitic jiapilla, and then 

 courses over the adjoining retina (a cilio-retinal artery), supplying the latter in part 

 in place of the central artery. 



