Mr. W. G. Horner on the Vascular Spectrum. 267 



are omitted in fig. 2. to prevent perplexity in comparing it 

 with fig. 1. The central region of the former was, however, 

 as clear of all vessels as I have represented it. 



Fig. 1. Fig. 2. 



Explanation of the Figures. 



Fig. 1. Vascular Spectrum, as seen in the right eye; + be- 

 ing the point of sight in the centre of the field. 



Fig. 2. The Central Vessels on a larger scale, exhibiting 

 the ultimate vascules of the spectrum, and the granu- 

 lated appearance of the foramen centrale. 



In fig. 1. the picture has about four times the linear dimen- 

 sions of the original, and in fig. 2. about twelve times. 



By experimenting with strong sunlight, admitted through 

 a large pinhole in a dark cardboard brought as close to the 

 eye as possible, I find (1) that the appearance of the luminous 

 surface is not so properly granular as fbrous, like plush, and 

 has irregularities which bear a strong resemblance to those in 

 Zinn PI. I. fig. 2. From this appearance, and another cir- 

 cumstance presently to be noticed, I suspect that this luminous 

 phenomenon is no other than the flocculent and delicately 

 reticulated envelope of the internal arterial surface of the 

 choroid, that portion of it, namely, which is included within 

 the punctum luteum. And (2) that the minuter vessels of the 

 spectrum are more variously dispersed than the figure ex- 

 hibits them, and that those of the upper and lower branches 

 actually appear to inosculate, as though one set were arteries 

 and the other veins. 



With regard to the granulated or silky spot, more exact 

 observations have proved (.'5) that it is not fixed, as I at first 

 believed, or at least that the principal mass of light which 



2 M 2 



