Observations on the structure of the central t'oveti of the liiinian eye. 9 



ture üf 1 part of glycerine to sixteen of spirit. The effect of this 

 treatment was to obviate the brittlenoss to whicli chromic acid pre- 

 parations are otherwise liable. An oblong piece of the retina including 

 the macula and fovea was then carefully cut out and after having 

 been stained in bulk with haematoxylin it was placed in gum and cut 

 by aid of a Wiliams' freezing microtome into a series of sections each 

 of which was mounted separately. The sections extend from the edge 

 of tlie macula lutea to just beyond the middle of the central fovea; 

 one section of the series passing, so far as we can judge, exactly 

 through the middle of the fovea. The sections vary in thickness, some 

 being fairly thin, others not very thin; but they are sharply stained 

 and perfectly transparent, so that it has been possible not only to 

 make out with great distinctness all the details which such specimens 

 are able to show, but also to obtain sharp micro -photographs of the 

 most important parts (Zeiss' apochromatic objectives having been em- 

 ployed for this purpose). The actual specimen from which the photo- 

 graphs whicli accompany this paper have been taken, is one which as 

 before said passes through the very middle of the fovea. The reasons 

 for considering that this section passes through the centre are: 



1. The depression of the external fovea (which as will be sub- 

 sequently seen is in this retina more acute than that of the internal) 

 passes its deepest point in this section^). 



2. The vertical course taken by the central cone -fibres and the 

 manner in which these and the more laterally situated cone-fibres can 

 be followed along their whole length from the limitans externa to the 

 outer molecular layer. It is obvious when we consider the oblique 

 course which the more peripheral cone fibres take, radiating as they 

 do from the middle, that they could only be followed out in this way 

 in a section which passes exactly through the centre. 



3. The fact that the cone-nuclei, which, from the edge of the 

 fovea, have been gradually leaving the limitans externa and appro- 



^) The line of the membrana limitans interna is distorted in this section by 

 a slight injury a little to one side of the centre so that it is not possible to draw 

 any inference as to the position of the section from the depth of the internal fovea. 

 This fovea is, moreover, so gradually carved that it would in any case be difficult 

 to say at which section the greatest curvature is reached. 



