1869.] Blood-vessel-system of the Retina of the Hedgehog. 357 



u Note on the Blood-vessel-system of the Retina of the Hedgehog 

 (being a fonrth Contribntion to the Anatomy of the Retina) ." 

 By J. W. Hulke, F.R.S.,, Assistant- Surgeon to the Middle- 

 sex Hospital and the Royal London Ophthalmic Hospital. 

 Received May 26, 1868*. 



The distribution of the retinal blood-vessels in this common British Insec- 

 tivore is so remarkable that I deem it worthy of a separate notice — only 

 capillaries enter the retina. 



The vasa centralia pierce the optic nerve in the sclerotic canal, and, 

 passing forwards through the lamina cribrosa, divide, at the bottom of 

 a relatively large and deep pit in the centre of the intraocular disk of the 

 nerve, into a variable number of primary branches, from three to six. These 

 primary divisions quickly subdivide, furnishing many large arteries and 

 veins, which, radiating on all sides from the nerve-entrance towards the 

 ora retinae, appear to the observer's unaided eye as strongly projecting 

 ridges upon the inner surface of the retina. When vertical sections 

 parallel to and across the direction of these ridges are examined with a 

 quarter-inch objective, we immediately perceive that the arteries and veins 

 lie, throughout their entire course, upon the inner surface of the mem- 

 brana limitans interna retinae, between this and the membrana hyaloidea 

 of the vitreous humour, and that only capillaries penetrate the retina 

 itself. 



In sections of the retina across the larger vessels the membrana limitans 

 may be seen as a clean distinctly unbroken line passing over the divided 

 vessels, with which it does not appear to have any direct structural connexion. 

 The relation of the hyaloidea to the large vessels seems to be more intimate, 

 but its exact nature can be less certainly demonstrated, owing to the ex- 

 treme tenuity of this membrane. In my best sections I saw the hyaloidea 

 also crossing the large vessels, as does the limitans, but excessively delicate 

 extensions of the hyaloidea appeared to me to lose themselves upon the 

 vessels. 



The capillaries, shortly after their origin, bend outwards away from the 

 large vessels, and, piercing the retina vertically to its stratification in a direc- 

 tion more or less radial from the centre of the globe, and branching dicho- 

 tomously in the granular and inner granule-layers, they form loops, the 

 outermost of which reach the intergranule-layer. As they enter the retina 

 the membrana limitans interna is prolonged upon the capillaries in the 

 form of a sheath, which is wide and funnel-like at first, but soon em- 

 braces the vessels so closely as to become indistinguishable from their 

 proper wall ; so that, notwithstanding the existence of a sheath, there is no 

 perivascular space about the retinal capillaries, such as His has described 



* Read June 18, 1868 : see Abstract, vol. xvi. p. 439. 



VOL. XVII. 2 E 



