22 SCHULTZE, ON THE RETINA. 
outer and thinner of which corresponds with the so-termed 
‘intergranular layer,’’ and the inner in the same manner corre- 
sponds with the “molecular layer” or outer part of the 
“layer of grey substance.” The membrana limitans externa 
in the fully developed organ does not constitute a continuous 
expansion, but is perforated with numerous closely placed 
openings, like the shelf of a bottle-rack. The membrana limi- 
tans interna, properly speaking, is also not a continuous 
membrane, but a reticulated tissue composed of the expanded 
ends of the radial trabecule or “fibres of Miller.” This 
fibrous framework supports the nervous part of the retina, 
which may be subdivided into six, or more properly, perhaps, 
seven distinct layers. These layers, proceeding from without 
‘inwards, are—l. The bacillary layer, composed of “ rods ” and 
“cones,”’ placed vertically on the periphery, and each lodged 
by its inner extremity in one of the openings in the outer 
limitary membrane. 2. The “ outer granule-layer,” com- 
posed for the most part of granular nucleated cells, connected 
with either the “rods ” or ““cones,’’ and traversed by the fila- 
ments proceeding from those bodies. 3. The “ intergranular 
layer,” which is constituted, as before remarked, in part of a 
fine, fibrous, trabecular ee intermixed a which is a 
still finer plexus of very delicate nerve- -fibres, for the most 
part, as it would seem, continuous with the terminal fibrille 
of the cone-filaments, and perhaps also in part with the ter- 
minations of the rod-filaments, although this has not been as 
yet clearly made out. 4. The inner granule-layer, contain- 
ing for the most part bipolar ganglion-cells and abundance of 
fine nerve-filaments. 6. The “ molecular layer,”’ which is of 
considerable thickness, and, like the “ intergranular layer,” 
apparently composed of an intricate interlacement of very 
delicate nerve-filaments and the fine trabecular network 
before mentioned. 6. The “ ganglionic layer,” constituted 
chiefly of large multipolar nerve-cells, each of which on its 
inner aspect appears to be connected with a fibrilla of the 
optic nerve, and on its outer to give off several processes 
which break up into the delicate fibrils contained in the 
molecular layer. 7. The layer of “ optic nerve-fibres,” which 
in most animals appear to have no sheath, but to represent 
axial filaments. 
The author’s researches have been directed more especially 
to the distinction between the “ rods” and “cones.” But 
his attention has been turned, not so much to their morpho- 
logical characters, with respect to which little now remains to 
be said, as to their relations to the other retinal elements, so 
that he might be able, if possible, to obtain some insight into 
their physiological differences. That such differences must 
