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NUNNELEY, ON THE RETINA. 
1. The columnar or bacillar layer, rods, Jacob’s mem- 
brane. 
2. Bulbous or conoidal bodies. 
3. Granular layers. 
4, Nucleated vesicular layer. 
5. Vascular layer. 
6. Fibrous layer. 
7. Hyaloidal cellular layer. 
1. The outermost layer of the retina is really a wonderous 
structure. It is quite peculiar to the retina, but is found 
in all animals where there is a retina, even in the eye-dot of - 
the “blind mole.” It consists of mimute cylindrical bodies as 
innumerable as the sand upon the seashore. ‘They are Rops 
or COLUMNS, arranged side by side, and stand perpendicularly 
to the centre of the eye; the outer ends are in close con- 
nexion with the choroid coat, the inner ends rest among the 
granules which form the third layer; they consequently 
stand at right angles to the fibrous expansion of the optic 
nerve. They may be traced uninterruptedly from the expan- 
sion of the optic nerve to the ora serrata; they are consider- 
ably the longest at the former situation, and appear gradually 
to decrease in length towards the fore part of the retina. 
They are so closely arranged as to constitute a complete coat. 
In man, mammalia generally, reptiles (except the chelonian,) 
and fish, they appear to be perfect cylinders, with clear, dis- 
tinct, straight, transverse ends. In chelonians and birds, 
there are a few cylindrical, but they are for the most part 
bulbous or conoidal; the larger end bemg outmost. They 
have been sometimes described as six-sided prisms; un- 
doubtedly not unfrequently they appear hexagonal—this, 
however, merely arises from their being compressed against 
each other, where not so they are perfectly round. In the 
frog and the toad by far the greater number are perfect 
cylinders, but I have seen some few amongst the mass with 
one end broader than the other. They are solid, perfectly 
transparent, highly refractive rods, quite straight in_ the 
living eye, but they very soon become variably distorted, as 
bent at right angles, particularly towards one extremity, the 
outer, or curled up at one end, like the hook of a walking- 
stick, as represented as the normal condition by Hassall ; 
but of which not a trace is to be found in the eye of an 
animal just killed. They then curl up into oval or circular 
rings, so as to look very much like cells, and may easily be 
mistaken for blood-cells; occasionally they split longitudi- 
nally, but far more commonly they become marked by 
