IN THE EYES OF CEKTAIN T.EPTILES. "5 
which may be distinguished the dark-coloured choroid. 
Close to this is generally placed a fold or reduplication of 
the retina, which is in general remarkably distinct. This 
fold (or folds, for, occasionally, there are more than one), 
either proceeds from the transparent point towards the in- 
sertion of the optic nerve, or close to it. Sometimes the 
fold seems, as it were, to lie over the transparent point, 
and partly to conceal it from view ; or the point is formed 
in the edge of the fold itself, as in apes ; but, in general, 
the fold runs directly from the insertion of the optic nerve 
upwards and inwards, passing very close to the edge of 
t\\Q Jhrameti centrale. It will readily be imagined, that 
the farther dissection of this part of the retina was attended 
with much difficulty, on account of the smallness of the eye- 
bail. On the inner surface of the retina, and covering even 
the transparent point, is an excessively delicate vascular 
membrane, apparently supporting the branches of the cen- 
tral artery of the retina. When we remove the retina from 
the choroid, the former of these membranes, in some speci- 
mens, divides readily into two very distinct, layers. The 
first, or that nearest the vitreous humour, is of an opaque- 
white, pulpy and thick ; the second, or that situated next 
the choroid, is thin, of a slight bluish cast internally, pale 
brown externally, and cannot be detached en masse from 
the choroid, though sufficiently large flakes may be forced 
off with the edge of the knife. Near the Point of Soem- 
mering inwards, towards the insertion of the optic nerve, 
and around the foramen centrale^ these two membranes are 
strongly connected witii each other, and cannot be separa- 
ted. When the whole of the membrane whicii we generally 
call retina is removed from the choroid, and drawn gently, 
towards the optic n^rve, there is evidently a circular aper- 
ture in the retina, constituting Jhramen cc7itrale, ..md 
