106 ON THE FORAMEN CENTRALE, , 
very sharp scissars the anterior third of the eye-ball^ 
including the cornea and iris : the lens and capsule of 
. the vitreous humour must now be very carefully re- 
moved with a fine brush. I have thought it worth 
while to mention the mode I adopt in displaying the 
retina, because, by its adoption, any one, whether ana- 
tomist or not, will readily ascertain the presence or ab- 
sence of this very extraordinary structure. 
The black point b, marking the entrance of the 
optic nerve into the interior of the eye-ball, may rea- 
dily be distinguished from the foramen centrale 
by the little marsupium which has been left attached 
to the former. I regret that the drawing had not been 
taken from the eye of the chameleon, in which the 
structure is naturally so greatly magnified. 
Fig. % The eye-ball viewed posteriorly, to shew that the 
transparent Point of Soemmering is really a foramen. 
The sclerotic c, and choroid J, have been removed, 
leaving the retina (marked in which the foramen 
(a) is distinctly visible. 6, marks the entrance of the 
optic nerve. 
Fig. 3. The foramen centrale^ fold, and yellow spot, as 
seen in the eye of apes. This latter figure is of the 
natural size ; the others are somewhat magnified. The 
letters refer to the same parts as in the former figures. 
Edinburgh, ) 
Seft 1. 18^3. j 
