Observations on the structure of the central fovea of the human eye. 1 3 



through the very centre; and M. Schnitze based his description of tlie 

 general structure and arrangement of the part largely upon abnormal 

 specimens ^). 



We have ourselves examined three other normal foveae, besides 

 the one here described : all three were fixed and hardened with osmium- 

 bichromate mixture. Two of these were cut in serial sections by the 

 paraffin-method and the third was imbedded in celloidin. In nearly 

 all points these three specimens agree with the one we have selected 

 for description but in one the dip of the inner fovea is sharper than 

 in the others and its diameter is somewhat less. The depth of both 

 foveae but especially of the outer, shows considerable variation. In all 

 however the outer fovea is very marked and the cones upon it are 

 very much longer than those on the rest of the retina. 



In drawing attention to the chief points which our specimens 

 illustrate it will perhaps be most instructive if on these points they 

 are compared in detail with the statements and representations of 

 previous authorities. 



1. As to the shape and size of the dejjression of the membrana 

 limitans interna which is commonly hnoivn as the fovea centralis 

 hut ivhich (as there certainly exists a corresponding depression of 

 the external limiting membrane) ive may distinguish as the internal 

 fovea. 



In the specimen figured this is a basin-shaped depression about 

 I'l mm. in horizontal diameter and with the margins, especially the 

 inner one, slightly raised beyond the general concavity of the inner 

 retinal surface (PI. I. Fig. 1). The slope of the sides and bottom is 

 fairly uniform and there is no sign of a flat fundus or central foveola 

 such as Kuhnt describes. The total depth of the depression is 013 mm.^). 

 Comparing this fovea with others which have been represented, those 



*) Two from eyes most of the layers of which were atrophied in consequence 

 of tumours and one in which the fovea was partly spoiled by a post mortem fold. 



^) Its surface appearance was not recorded, but in two well-preserved osmium- 

 bichromate specimens, entirely free from folds, the fovea appeared as a perfectly 

 circular pit when viewed from the surface. It has the same appearance also in 

 the monkey. 



