339 
in the Retina of the Eye . 
light, had an appearance of four rays, at right angles, as ex- 
pressed in the annexed plate. (SeeTab. XVII. fig. 3.) Its situa- 
tion, respecting the optic nerve, was precisely the same as in 
the human eye. As I considered this to be a fact of some im- 
portance, since it proved the aperture in the retina to be a part 
of the structure of the eye, generally, and not a peculiarity in 
the human eye, I requested Sir Joseph Banks, Sir Charles 
Blagden, and Dr. Baillie, to examine it: to all of them it 
appeared very distinct. After having shown it to those gen- 
tlemen, and having an accurate drawing made of it, I preserved 
that portion of the eye in spirits ; where the aperture in the 
retina can still be distinctly seen, but the radiated appearance 
is lost. 
In the eye of a bullock, prepared in the same manner, I 
looked in vain for a similar appearance : if it existed, and 
bore any proportion to the size of the eye-ball, as it ap- 
pears to do in the human eye and that of the monkey, it 
must have been very visible. The concave surface of the 
retina was examined in different lights, under a variety of cir- 
cumstances, and by magnifying glasses of different powers, 
but still no aperture could be discovered. I was, however, 
very much struck, while looking at the optic nerve, to see 
something in the vitreous humour, (in consequence of a per- 
son accidentally shaking the table,) that had not been before 
observed. 
This proved to be a semi-transparent tube, resembling in its 
coats a lymphatic vessel, rising from the retina, close to the 
optic nerve, on the temporal side of its insertion, and coming 
directly forwards into the vitreous humour, in which it was 
lost, after being distinctly seen for -^-ths of an inch of its course. 
X x 2 
