Observations on the structure of the central fovea of the human eye. 21 



similar to those which Cajul has described iu the fovea of the bird 

 and reptile. 



There are in our sections a very few large cells, not more than one 

 in each section (Figs. 3 and 4), resembling in size and general appear- 

 ance the ganglion -cells, but placed amongst the inner granules, near 

 to but not quite at the centre of the fovea; whereas the ganglion-cells 

 as a lâjev have thinned off and ceased altogether some little way 

 (0-086 mm.) from this point. Since in several of these isolated nerve- 

 cells it is possible to see a stalk-like periJDherally directed process 

 like that of the ganglion cells we are constrained to regard the cells 

 in question as "dislocated" nerve-cells. We have not been able to 

 determine the existence of basal or horizontal cells or of "amacrines" 

 at this part, but the methods we have employed are not adapted for 

 displaying these. The same may also be said regarding the connections 

 of the concatenated elements of the retina. 



10. The hyaloid membrane of the vitreous humour is gradually 

 thinned out as it passes over the fovea. At the periphery of the 

 depression it is about 0-003 mm. in thickness but at the very centre 

 it is n mere film too thin to be measured. As elsewhere in the 

 retina it is entirely separate and detachable from the limitans interna, 

 which as in other parts is apparently formed entirely of the conjoined 

 inner extremities of Miillerian fibres. The form of these fibres at this 

 part and their exact relations to the retinal elements are not apparent 

 in our sections. 



We append some measurements showing the thickness in millimeters 

 of the retinal layers, taken respectively (1) from the macula lutea, 

 1"5 mm. mesial and lateral to the edge of the fovea; (2) from the 

 edge of the fovea (also mesial and lateral); and (3) from the very 

 centre of the fovea. 



