330 GEORGINA SWEET. 
lined with flattened cells, and branching shghtly in the retina. 
This is also in close relation with the internal fibrous layer of 
the retina, and with a more or less defined group of ganglion 
(7) cells. The remaining layers of the retina are compara- 
tively clearly defined, the inner nuclear layer and inner 
molecular layers are hard to separate, but otherwise the nerve 
fibre, outer molecule, outer nuclear, and rod and cone layers 
are all well seen (PI. 6, fig. 2). The internal and external 
limiting membranes are often very distinct. The layer of 
rods and cones separates easily from the pigment layer, owing 
to the great shrinkage of the retina which takes place after 
death or during preservation or preparation. Indeed, it 
appears to me that there may be, in life, a small posterior 
chamber occupied by some more fluid material than the 
ordinary vitreous humour contained therein. 
In the outer layers of the retina, just opposite the gap in 
the pigment layer, is a similar space for the exit of ‘the fibres 
to form the optic nerve. 
Dorsally to the median line, the whole retina except the 
pigment layer is attached to the iris, otherwise lying freely 
in the optic ball, but passing ventrally the retinal mass 1s 
seen to lose this connection and become associated with the 
back of the eyeball. Near the median line of this area the 
sclerochoroid and the fibrous layer behind the conjunctival 
sac begins to be drawn (PI. 6, figs. 1 and 2), so that the 
eyeball and surrounding fibrous layer has here a more pear- 
shaped structure. 
At about the same horizontal plane the anterior chamber 
of the eye is lost, the iris having merged into the wall of the 
eyeball. Somewhat more ventrally to this again the gap in 
the pigment and outer retinal layers at the inner end of the 
longitudinal median line of the eye becomes much bigger and 
more definite; through it there passes backwards a bundle 
of optic nerve-fibres. This runs out and down the middle of 
the fibrous stalk of the now pear-shaped eyeball, this fibrous 
layer, as it tails out, forming the sheath of the optic nerve. 
