232 NUNNELEY, ON THK. RETINA. 
of a flattened form, like pieces of money (hence named by 
him nummular layer), with the flat surfaces corresponding with 
the thickness of the retina; while Kolliker says the inner 
are larger than the granules of the outer layer, and arranged 
with their long axes in the direction of the thickness of the 
retina. Ifa section of the dried retina of man, the sheep, or 
the ox, be examined with water or dilute spirit, there is 
no difficulty in perceiving this irregular line of very minute 
granular matter and indistinct fibres with flattened globules 
arranged horizontally in the length of the retina, as described 
by Bowman, and not vertically in the direction of the thick- 
ness, as figured by Kolliker; but it is by no means so easy to 
detect this separation into two layers in the perfectly fresh 
retina. I have sometimes fancied it was to be seen in the 
bullock and sheep, but I have so often not been able to find 
it, that, knowing how greatly every portion of the retina is 
changed by all fluids, and how little dependence is to be 
placed im appearances there found, I feel doubtful if there 
really be two layers. The globules placed most internally 
are smaller than the external. It is, I think, in the inner- 
most part of this and the next layer that the capillaries of the 
blood-vessels are principally situated, though Bowman says, 
they have no blood-vessels, and certainly none appear to be dis- 
tributed in the mass or thickness of the layer. On the addition 
of water and many other fluids, the globules separate from 
each other, float about, dilate, rupture, and disappear, leaving 
only fine granules, which also dissolve. They are rendered 
more distinct and refractive by dilute acetic and chromic 
acids, in which they are well seen. 
The rods rest upon and are imbedded amongst them, each 
rod being intimately connected with one globule, which often 
remains attached to the end of the rod when the rods are 
detached from each other. This has given rise to the im- 
pression of the rod having a head like a nail, but in a few 
minutes it usually becomes detached, and is then seen to 
resemble the other globules. It may be doubted how far 
the connexion is organic or not, as the same globule may be 
seen, 1f it happen to come in contact with another rod, to 
adhere to any part of its surface. 
4. On the inner surface of the granular or nuclear layer 
is the vesicular layer—“ gray vesicular matter of retina’”— 
“ cineritious cerebral substance,” which is a very thin layer, 
composed of finely granular or cellular matter, of apparently 
the same nature as the last, and probably more correctly to 
be regarded as its commencing portion than as a distinct 
structure, in which also are numerous larger and clear trans- 
