132 Royal Society ^ 



preaching our own days, is a new example fitted to demonstrate, 

 on the one hand, the existence of close relationships between 

 the famia of these isolated lands and the zoological population 

 of the Australasian region, and, on the other, the complete 

 separation of this fauna from that of the great African conti- 

 nent. 



PROCEEDINGS OF LEARNED SOCIETIES. 



ROYAL SOCIETY. 



June 18, 1868. — Lieut.-General Sabine, President, in the Chair. 



" Note on the Bloodvessel-system of the Retina of the Hedgehog." 

 By J. W. HuLKE, F.R.S., Assistant-Surgeon to the Middlesex Hos- 

 pital and the Royal London Ophthalmic Hospital. 



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

 Insectivore 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 intra- 

 ocular disk of the nerve, into a variable number of primary branches, 

 from three to six. These primary divisions quickly subdivide, fur- 

 nishing many large arteries and veins, which, radiating on all sides 

 from the nerve-entrance towards the ora retinse, appear to the ob- 

 server'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 ob- 

 jective, we immediately perceive that the arteries and veins lie, 

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

 brana limitans interna retinse, between this and the membrana 

 hyaloidea of the vitreous humour, and that only capillaries pene- 

 trate 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 extreme tenuity of this mem- 

 brane. In my best sections I saw the hyaloidea also crossing the 

 large vessels, as does the limitans; but excessively delicate extensions 

 of the hyaloidea apjjcared 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 strati- 

 fication hi a direction more or less radial from the centre of the globe, 

 and branching dichotomously in the granular and inner granule- 

 layers, they form loops, the outermost of which reach the inter- 

 gvanulc layer. As they enter the retina, the membrana liinitant) 



