Monthly MicroscopicMll 
Journal, Nov. 1, 186'.). J 
Histology of the Eye. 
243 
dark edged nerve-fibres occur. In both situations, ganglion-cells are 
present. These latter were, I think, discovered first by H. Miiller 
and by Schweigger. Their demonstration is not always easy, or 
even a certain matter. 
In front of the ora serrata, the inner surface of the choroid ex- 
hibits a circle of vascular plaits. First rising gently above the 
surface, and then projecting freely, these compose the pars striata of 
Zinn and the familiar ciliary processes. They are covered with a 
pigmented pavement-epithelium, the cells of which are less uniform 
than those of the posterior segment of the choroid. Each ciliary 
process is a vascular plait, composed of large capillaries, which 
receive their arterial blood by two or three branches, which come 
off directly by a short trunk from the circulus arteriosus major 
iridis, or which arise nearly as often together with one of the arteries 
proceeding to the iris. The little arteries enter the outer surface 
(or rather edge) of the processes ; and small veinlets run along the 
inner or free border ; and they form a long meshed venous capillary 
plexus, which conveys the venous blood backwards to the vasa 
vorticosa. This venous capillary plexus not only transmits all the 
blood from the ciliary processes, but it also receives veins from the 
iris, as also some from the ciliary muscle. 
In all vertebrates (except the lowest fishes, e. g. myxine and 
lancelet) a section vertical to the surfaces of the retina shows the 
following superposed layers. 
First, there is a layer of columnar bodies, the rods and cones 
abutting against the choroid — the bacillary layer, known also as 
Jacob's membrane. To this succeeds the layer of corpuscles called 
the outer granules. Next follows a fibrillated stratum — the inter- 
granule layer ; then another layer of corpuscles, the inner granules ; 
next to this the layer, called by some the granular layer, by others 
the grey vesicular or grey nervous layer ; then a stratum of ganglion- 
ceUs ; and, finally, a stratum of optic nerve-fibres, bounded internally 
by a thin membrane, the " membrana limitans interna retinse." 
In all these layers, nervous and connective tissues are intimately 
commingled ; and it is just this interpenetration of the two tissues 
which constitutes our principal difficulty whenever we attempt to 
decide the nature of a particular retinal element. 
Before proceeding to a detailed account of its tissues, a few 
words on the best methods of studying the retina may be useful to 
some readers. First, it is absolutely essential that the eyes be 
perfectly fresh — the lapse of half-an-hour after the circulation has 
ceased, or even of a few minutes if the eye have been opened, makes 
differences in the appearance of the bacillary elements. Next, the 
outer surface of the fresh retina should be carefully scrutinized, in 
order to learn if both rods and cones are present. The latter will 
be known by their greater stoutness, and by their outer ends lying 
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