360 The Blood-vessel-system of the Hedgehog. ["SSi, juneTff' 
of a number of animals experimented upon by my friend and co- 
labourer, Dr. Greo. J. Ziegler, animation was promptly restored in 
every case by tbe injection of nitrous oxide water into the intestines 
of the animals. In these cases the efficacy of this agent in supply- 
ing oxygen to the blood and the nervous mass was most satisfactorily 
demonstrated. 
If we assume that the influence of anaesthetics is dependent not 
upon a direct action on thenerve centres, but to an altered condition 
of the blood and the suspension of oxygenation, we must apply the 
same principle to aU diffusible stimulants. — The Dental Cosmos, 
YII. — Note on the Blood-vessel-system of the Betina of the 
Hedgehog. By J. W. Hulke, F.E.S. 
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 cajpillaries 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, 
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 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 connection. 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 
membrane. In my best sections I saw the hyaloidea also crossing 
the large vessels, as does the limitans, but excessively dehcate 
extensions of the hyaloidea.appeared to me to lose themselves upon 
the vessels. 
