604 REPORT—1899, 
part of the cup } mm. The dipping inwards of the external limiting 
membrane causes a circumferential cup around the innerone. The inner 
and outer ganglionic layers, as well as the inner fibrous layer, are reduced 
to very small proportions, there being in a section 10 » thick only 15 
nuclei of the outer ganglionic layer scattered along the margin of the 
macula. The thickness of the layer of the nuclei of the rods and cones 
(outer nuclear) is greater when measured from within outwards in the 
part opposite the macula than in any other region of the retina (55 y) ; 
this is largely due to the loose arrangement of the cone nuclei. The most 
interesting point is the peculiar arrangement of the rods and cones. 
Opposite the macula the cones are erect, i.e. their inner, middle, and outer 
segments are all in a straight line ; outside the macula, however, the outer 
segments of both rods and cones all point towards the centre of the 
macula, the angle which these segments make with the middle ones 
depending upon the distance of the elements from the yellow spot. The 
different segments of the cones are of the same length, whether the part 
examined is within or outside the macula ; there is thus no evidence of 
the shortening of the inner and middle cone segments which is present in 
the macula region of the human retina. 
The transverse dimension of a cone increases steadily in proportion to 
the distance of the region examined from the macula. The large extent 
of the increase on the temporal side is shown in the following table :— 
Distance from Centre of Transverse Dimension of Cones 
Optic Disc. in Micromillims (y). 
4 millimetre . : : 3 . 4:25 
1 ” . . . . . 4 . 
ie : ; i : "4-95 Nasal side 
2 millimetres . 4 P ; ~ Ab 
Macula A 4 ; 5 . 125 Macula 
3 re - 2°5 
33 4:5 
43 ) 55 
5 Es 65 : 
62 4 15 Temporal side 
7% ‘ . 875 
9 a 5 : 5 5 . 10 
Both the inner and outer ganglionic layers reach their maximal 
development on the temporal side of the retina, the greatest thickness, 
measured from within out, of the inner ganglionic layer being 50 m on the 
temporal and 14 to 16 » on the nasal side, that of the outer layer 55 u 
on the temporal and 38 uw on the nasal side. On the other hand, the layer 
of the nuclei of the rods and cones is nearly equal in thickness on these 
two sides of the retina. 
There is in the monkey a further sharp division of the outer fibrillar 
(molecular) layer into a part consisting of the internal processes of the 
nuclear layer of the reds and cones, and a part consisting of the external 
processes of the outer ganglionic (inner nuclear) layer ; the fibrils in. the 
former case run horizontally near their terminations, in the latter at right 
angles to this distribution. 
