VOL. LXXXVIII.] PHILOSOPHICAL TRANSACTIONS. 827 



discovery in the anatomy of the human eye, made by a professor of Mentz, Mr. 

 Soemmering; permit me therefore to say something on the subject. He was dis- 

 secting, in the bottom of a vessel filled with a transparent liquid, the eyes of a 

 young man who had been drowned, and was struck on seeing, near the insertion 

 of the optic nerve on the retina, a yellow round spot, and a small hole in the 

 middle, through which he could see the dark choroides, looking at the surface of 

 the retina which covers the vitreous humour. He dissected other human eyes, and 

 constantly, when the dissection was carefully made, found the hole of the retina 

 seemingly at the posterior end of the visual radius, nearly 2 lines on the temporal 

 side of the optic nerve, and the hole surrounded by the yellow zone, of above 3 

 lines in diameter. The hole of the retina is not directly seen, being covered with 

 a fold of the retina itself. An anatomist of Paris dissected many eyes of quadrupeds 

 and birds, and found the yellow spot and hole in no animal but the human kind. 

 Should you think that nature has intended this hole to grow large when the eye is 

 opposed to a strong light, and thereby cause a great part of the rays to fall on the 

 choroid, and vice versa, when the eye is in darkness? And the want of such a con- 

 struction in animals, is it owing to a greater power of augmenting or diminishing 

 the pupil, than in men? If Messrs. Mariotte and Le Cat should come to life again, 

 they would find, in that hole, the explanation of the phenomenon of the 2 cards, 

 one disappearing at a certain distance from 1 eye, &c. which may be explained by 

 saying, that where the optic nerve enters the ball, there is no choroid, and so 

 no vision. 



" I dissected some human eyes a short time after I had read the discovery, and 

 found the spot, the ruga concealing it, and the yellow zone. The best way I 

 think to see them, is to take oflf the half posterior part of the sclerotica, then the 

 correspondent part of the choroid; both must be cut round the insertion of the 

 optic nerve. The retina is to remain bare and untouched, sustaining alone the 

 vitreous humour ; then you may see the round spot, that reaches the optic nerve, 

 and a fold of the retina, marking a diameter of the spot. Then, if you press the 

 ball a little with your finger, so as to push the vitreous humour rather near the 

 bottom of the eye, the ruga is unfolded, and you will see the hole perfectly round, 

 of -^ of a line in diameter, and its edges very thin. All this can be seen on the 

 inside of the eye, but not so perfectly; and in that case you must make the ob- 

 servations in water." 



Many months elapsed, after the receipt of this letter, before I could procure an 

 eye in a proper state for observing this aperture in the retina; but, in the course 

 of last month several opportunities offered, and I saw the appearance described by 

 Mr. Maunoir very distinctly. The mode I adopted for examining the retina, was 

 that of removing the transparent cornea; then taking away the iris, and wounding 

 the capsule of the crystalline lens, so as to disengage the lens, without removing 

 that part of the capsule which adheres to the vitreous humour; by which means, 

 the retina remained undisturbed, and could be accurately examined, when a strong 



