TRANSACTIONS OF THE SECTIONS. 7 
Meeting, I have shown that the small circular area at the end of the optical axis, 
whether it be retina or choroid, retains light longer than the general retina, after the 
eye has been exposed to light; and I have recently observed that certain points of 
that membrane, situated apparently near its termination at the ciliary processes, have 
even a greater retentive power. In order to observe this curious phenomenon, we 
must extinguish, suddenly, a gas-flame, to the light of which the eye has been for 
some time exposed. We shall then observe a number of bright luminous points 
arranged in a circle, the diameter of which is about 72°. These bright points, or 
stars, apparently placed at equal distances, vanish so quickly that I have found it 
very difficult to determine their number. They may amount to fifteen or twenty. I 
have sometimes observed them upon extinguishing a candle, and also upon quickly 
shutting the eyes. The parts of the retina from which these points of light emanate 
are probably places where the retina is attached to the ciliary ring, or other parts in 
the interior of the eye, and may therefore be detected by the anatomist. 
On Vision through the Foramen Centrale of the Retina. 
By Sir Davip Brewster, A.A, F.RS. LS EB. 
At the Meeting of the British Association which was held at Belfast 1 gave an 
account of a case of vision, in which it was performed entirely by the choroid coat, 
or rather through the foramen centrale of the retina. The space of distinct vision, 
as ascertained by the number of minute printed letters which the patient could read, 
was 42°, the angle subtended by the foramen, which I had previously determined by 
experiment. In this case the paralysis of the retina was permanent, and the patient 
was blind, with the exception of the small amount of vision which he enjoyed through 
the foramen. In the case to which I now call the attention of the Section, paralysis 
was temporary, and was accompanied with severe headaches ; but as soon as the 
patient recovered her health, the retina resumed its usual functions. In order to find 
the area of distinct vision, the patient observed with care the number of small and 
sharply printed Jetters which she could read at a certain distance from the eye ; and 
upon measuring the breadth of these letters, and their distance from the eye, I found 
that they subtended an angle of 44°, corresponding with the size of the opening in 
the retina. These facts, when viewed in connexion with those which I described at 
the Swansea Meeting, may throw some light on the functions exercised by the retina 
as a whole, or by some of its individual layers. I have placed it beyond a doubt, that 
the membrane, whether choroid or retina, which occupies an area of 42° at the ex- 
tremity of the optical axis of the eye, is in certain cases less retentive of luminous 
impression, and in others more retentive than the retina. If the microscope proves 
that there is no retina corresponding to that area, we must consider the choroid coat 
as the seat of vision. If it should prove that any one of the layers of the retina 
occupies that area, while the rest are wanting, it will be manifest that that layer is 
the seat of vision, or rather of luminous impressions. 
On certain Abnormal Structures in the Crystalline Lenses of Animals, and 
in the Human Crystalline. By Sir Davip Brewster, K.H., F.RS. 
L. & £. 
In examining, many years ago, the structure of the crystalline lens in the Mam- 
malia, Birds, Fishes, and Reptiles, the results of which are printed in the ‘ Philo- 
sophical Transactions,’ I observed several deviations from the normal structure of 
particular lenses, which I did not think important enough to publish. Having found, 
however, that these abnormal structures have been in some instances taken for the 
true structures, and that structures accurately determined have, on their authority, 
yee considered erroneous, it is necessary to draw the attention of anatomists to the 
subject. 
In the lenses of several large whales brought home by the Arctic navigators, | 
found that the fibres were related to four rectangular septa* ; but in one lens J found 
* Phil. Trans. 1836. plate 5. figs. 1, 2, No. 4. 
