104 DR KNOX ON THE FORAMEN CENTRALE 
VI. — Additional Observations relative to the Fo- 
ramen centrale of the Retina in Reptiles. 
By Robert Knox, M. D. 
Member of the Wernerian Natural History Society, and of the Medico- 
Chirurgical Society of Edinburgh. 
{Read November 1823.) 
Since my first observations on the discovery of the Jh^ 
ramen centrale in reptiles were written, I have had an 
opportunity of examining, through the kindness of Profes- 
sor Jameson, the anatomy of a large variety of the Cha- 
meleon, which had been sent to the Museum of the Uni- 
versity by the Marchioness of Hastings. The conjecture 
offered by me formerly, that the foramen centrale would 
be found to exist in the eye of this animal, was now con- 
firmed ; for the whole of this very singular structure, viz. 
the foramen^ and the fold of the retina, are remarkably 
developed in the chameleon, and actually much larger than 
in the human species. There extends also from the entrance 
of the optic nerve to the foramen^ a fissure, which, how- 
ever, is not real, but apparent : this semblance of a fissure 
