264- Mr.W. G. Horner on the Vascular Spectrum. 



slowly backwards and forwards edgewise, so that the light 

 may traverse the interval between the cornea and the angle or 

 lid of the eye. 



6. The drawing (fig. 1, p. 267.) exhibits, with as much accu- 

 racy as my slender graphic skill admits, the result of numerous 

 and varied observations of the vessels of my right eye. The 

 cross'( + ) indicates the centre of the field of view, or the point 

 of direct vision. Beneath is the origin of the larger vessels, 

 which in its average situation falls within the range of the 

 punctum ccecum. To exhibit the more minute vessels, which 

 either from my perception improving by habit, or possibly 

 from continued excitement, appeared much more numerous 

 in my later than earlier trials, fig. 2. is an enlarged figure of 

 the more central vessels, and of the peculiar appearance of 

 the central portion of the ground of the picture. 



7. At the centre ( + ) of the ground of the picture, which 

 " corresponds to the projection of the foramen centrale," C. W. 

 observed a crescent-like appearance, indicating in his opinion 

 " a slight convexity or concavity in the retina at that point." 

 In my own eye, whether the right or the left, no trace of 

 such a crescent is found, but the appearance of a granulated 

 texture in the level surface, like a number of exceedingly 

 minute polished spherules collected within an obscurely de- 

 fined circular space, as represented in fig. 2. 



8. This circular spot is quite fixed, while the eye continues 

 steady ; and generally speaking, it is quite clear even of the 

 minute vessels, which appear almost equally spread in every 

 other part. But in waving the light over a considerable an- 

 gular portion of the eye, some of those vessels would intervene 

 between the sight and the central spot, indicating that the 

 vessels and the ground on which they were projected were on 

 different surfaces, contrary to what has been hitherto believed. 



9. This important fact was corroborated by the phenomena 

 observed about (0) the origin of the vessels, which was mani- 

 festly on different sides of the punctum ccecum, according as 

 the light fell far on the inner or the outer angle of the eye. 

 The situation of the head of the optic nerve was marked not 

 only by the usual indication, which in these weak lights is 

 less distinct than usual, but by the occasional brightness that 

 flashed upon it, when a strong light was suddenly thrown quite 

 in the angle of the eye. 



10. But the most available proof of this fact, was the ap- 

 pearance of the entire spectrum when referred to some distant 

 part of space. For, the eye being kept perfectly steady, the 

 image, with a sensibly uniform motion of all its parts, followed 

 the motion of the lens. This proved that the vessels which 



