232 DR KNOX on the Philosophical Anatomy 



Since that period I have repeated, with as much exactness as 

 possible, most of the dissections on which my former essay was 

 founded, and by employing very delicate coloured injections, 

 with which the bloodvessels of the eye were filled in several ani- 

 mals, I have thought it might not be uninteresting to state 

 briefly the result of these investigations to the Society, avoiding 

 as much as possible all tediously minute anatomical details. 



I. Of the Retina. 



I regret that it has not been in my power to extend my re- 

 searches into the structure of this most important membrane of 

 the e.ye in the human subject ; the obstacles in this country to 

 such dissections being considerable, and not to be overcome by 

 any individual not a teacher of anatomy : but I have seen 

 enough to convince me, that the first views adopted by me, re- 

 lative to the two most important points for investigation, viz. 

 the foramen centrale of the retina, and the mode in which the 

 membrane terminates anteriorly, are correct. Many of the mem- 

 bers of this Society are no doubt aware, that two distinct 

 opinions have been held relative to the nature of the discovery 

 of SCEMMERING ; some anatomists viewing the transparent point 

 in the axis of vision, (which he supposed peculiar to the hu- 

 man subject), as a distinct foramen, or absolute perforation of 

 the retina ; others, as the immortal CUVIER, considering it mere- 

 ly as a transparent point, and that there is no real deficiency of 

 the retina, but that the nervous membrane at this point merely 

 remains transparent after the death of the animal, whilst the sur- 

 rounding portions of the retina become opaque. They argue, 

 therefore, that the foramen centrale, or transparent point of 

 SCEMMERING, does not exist till some time after the death of the 

 animal. 



