328 PHILOSOPHICAL TRANSACTIONS. [ANNO 1798. 



light was thrown into the eye. The aperture in the retina, surrounded by a zone 

 with a radiated appearance, was distinctly seen, on the temporal side of the insertion 

 of the optic nerve, and about £ of an inch distant from it, apparently a little below 

 the posterior end of the visual radius. The aperture itself, in this view, was very 

 small. After having viewed it in 2 different eyes, I took an opportunity of showing 

 it to Sir Jos. Banks and Sir Charles Blagden, who both saw it with the same degree 

 of distinctness. 



At first, I believed it necessary to have a very fresh eye for demonstrating this 

 aperture; but I have since found, that it is more readily seen in an eye 2 days 

 after death; the zone, which is the most conspicuous part, being of a lighter colour 

 the first day, than it is on the 2d. I have also succeeded in preserving the pos- 

 terior part of the eye in spirits, without destroying the appearance of this aperture. 

 I am induced to make this remark, by recollecting that a celebrated anatomist of 

 Edinburgh denied, in his last publication, that the anterior lamina of the cornea 

 can be separated from the others, as a continuation of the tendons of the 4 straight 

 muscles of the eye, for no other reason than because he could not succeed in the 

 demonstration of it; the failure 'probably arising from the eye not being sufficiently 

 fresh to admit of such a separation. In separating the vitreous humour from the 

 retina, I found a greater adhesion at this particular part; and, when the vitreous 

 humour was removed, the retina was pulled forward, forming a small fold, in the 

 centre of which was this aperture. This doubling was sometimes produced by en- 

 deavouring to cut through the vitreous humour, to disengage the crystalline and its 

 capsule. 



After having made the preceding observations on this singular appearance in the 

 human eye, I found, in Dr. Duncan's Annals of Medicine for 1797, an account 

 of a publication concerning it by Professor Reil, entitled, the plait, the yellow spot, 

 and the transparent portion of the retina of the eye. After these are described 

 separately, the following circumstances are mentioned. " Soemmering takes this 

 appearance to be a real hole. Buzzi, on the contrary, thinks that it is merely a 

 transparent and thin portion of the retina. Michael is seems to agree with him. 

 Reil and Meckel are rather in favour of the existence of an actual hole. Michaelis 

 saw the plait more distinctly in foetuses of 7 or 8 months, than in adults; and the 

 transparent portion lay concealed within it, but the yellow spot was wanting: nor 

 is it to be observed in the eyes of newly-born children. After the first year, it 

 becomes somewhat yellow, and the depth of the colour increases with the age of 

 the subject. Soemmering says that this spot is pale in children, bright yellow in 

 young people, and becomes again pale in old age. Its degree of saturation seems 

 to be intimately connected with the state of vision: it constantly diminishes, in 

 proportion as vision is obstructed. Where one eye only is diseased, in it the yellow 

 spot is wanting, and the plait is small and wrinkled; while in the sound one they 

 are rather more distinct than usual. Michaelis discovered no vestige of these ap- 

 pearances in the eyes of dogs, swine, or calves." 



