FOVEA CENTRALIS OF THE HUMAN RETINA. 
Ill 
the increase of outer granules connected with the occurrence of rods towards the border 
of the macula. 
The relation of the outer granules to the cones and rods (figs. 2 & 3) (mentioned in 
the description of the bacillary layer) indicates them to be nuclei of the inner segments 
of these. In fresh specimens they are roundly oval bodies. I have not been able to 
distinguish any constant difference between those associated with cones and those with 
rods. The lozenge-shape of some granules in chromic-acid preparations results, I suspect, 
from their compression by the sheathing membrane of the rod or cone which shrinks under 
the action of the acid, or from traction exerted upon them by the cone- or rod-fibre. 
The fibres produced from the inner segments of the cones and rods — primitive bacillary 
fibres (some of which connect these with the outer granules, fig. 1 , 2 ) — traverse the layer 
obliquely from its outer to its inner surface, and radially from the centre of the fovea 
towards the ora retinse. At the inner surface of the layer they combine in a plexus 
(fig. 1, 3 , Cone-fibre plexus), which at the centre of the fovea (where the outer granule- 
layer is absent) lies between the bacillary and inner granule-layers, but at the margin 
of the fovea between the outer and inner granule-layers. The thickness of this layer 
(which in the chameleon I termed the cone-fibre plexus, H. Muller’s intergranule-layer) 
at the margin of the fovea equals or slightly exceeds that of the combined outer and 
inner granule-layers. The general direction of the bundles of the plexus coincides with 
that of the primitive bacillary fibres in the outer granule-layer ; it becomes, however, 
less oblique in the inner part of the plexus, where the bundles run nearly parallel to 
the surface of the inner granule-layer. 
These inner bundles midway between the centre of the fovea and the edge of the 
macula form a stratum parallel to the surface of the inner granule-layer. Beyond this 
point, with increasing distance from the centre of the fovea, the obliquity of the bundles 
increases until at the margin of the macula their direction is vertical. 
At its inner surface the bundles of the plexus (fig. 4) resolve themselves into primi- 
tive fibres which enter the inner granule-layer (fig. 1, 4 ) through a granular stratum 
of finely areolated connective tissue. At the edge of the fovea and at the border of the 
macula, where the bundles of the plexus are very oblique or nearly vertical, the primi- 
tive fibres pursue the same direction for a short distance in the inner granule-layer, but 
where the bundles are parallel to the surface of the inner granule-layer, the resultant 
fibres pass off nearly vertically into this layer*. 
* An oblique fibrillation has long been known in the intergranule-layer of the human macula lutea. Bergman 
seems first to have described it as a natural appearance 1 . 
H. Muller and Kolliker originally regarded it as a post-mortem or an accidental change ; but subsequently 
Muller, having discovered the oblique fibres in the chameleon’s macula, saw their correspondence to the oblique 
fibres in the intergranule-layer of the human macula, and acknowledged the oblique direction of these to be 
natural 2 . 
Kolliker a year later described two forms of fibrillation in the human macula, and left it undecided which 
1 Bergman, Ztsch. f. rat. Med. N.F. V. S. 245. 
2 H. Muller, Wiirzb. Naturwiss. Ztsch. Bd. in. S. 31. 
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