INSIDE THE EYE. 463 
maintaiii dilatation during several hours. This acts also per- 
fectly well with rabbits or cats. 
The first thing seen is the red reflection of the choroidal 
vessels showing through the transparent retina; and when 
the eye observed is directed upwards and inwards, we see the 
usually circular disc of the optic nerve, encircled by a double 
ring, cream-coloured or very faintly roseate or grey, and sur- 
rounded by the red choroid. The two rings are the aper- 
tures in the choroid and sclerotic, of which the former is the 
smaller. From out this disc we see springing the retinal 
artery and retinal veins, sometimes centric, at others excentric 
in their passage. The artery is easily recognized as being 
somewhat smaller in calibre, and of a fighter red. The artery 
usually divides into a superior and inferior branch, each of 
which subdivides forthwith into two secondary branches, and 
these again continue to subdivide, dichotomously, running for- 
ward to the anterior limits of the retina. The veins, which 
are somewhat larger and deeper coloured, usually pierce the 
disc of the optic nerve in two trunks. Pulsation may oc- 
casionally be detected in the veins by watching carefully their 
colour, which seems to change at each impulse just where 
they pass over the edge of the optic disc and bend to pierce 
the nerve. 
Fuller details of the ophthalmoscopic appearances of healthy 
eyes, both human and animal, will be found in Zander^s trea- 
tise, excellently edited and translated by Mr. E. B. Carter, of 
