on the Structure of Nerves. 11 
which, from their position, gave that appearance; but every 
observation that was made was in proof of their being conti- 
nued fibres. 
From these experiments, the internal structure of the optic 
nerve appears to be made up in the following manner: 
At its origin from the brain, it consists of thirty or forty 
fasciculi or bundles of extremely small opaque pulpy fibres, 
the interstices between which are filled with a transparent 
jelly. As the nerve goes farther from the brain, the fasciculi 
form smaller ones, of different sizes. This is not done by a 
regular subdivision, but by a few fibres going off laterally from 
several large fasciculi, and being united, forming a smaller one : 
some of the fasciculi so formed, which are very small, unite 
again into one. In this way, the fasciculi gradually diminish in 
size, and increase in number, till they terminate in the retina. 
Near the eye, where the fasciculi are most numerous, the 
substance of the nerve has a considerable degree of transpa- 
rency, from the number of transparent interstices between 
them ; but this is less the case nearer the brain, where the in- 
terstices are fewer. 
In the optic nerve of the cat, the structure is the same as in 
the horse ; but, from the smallness of the parts, less fitted for 
investigation. Near the eye, its internal substance is more 
transparent than the corresponding part in the horse. 
To see how far this structure was peculiar to the optic nerve, 
similar experiments were made upon the internal substance of 
the fifth and seventh pair of nerves, near their origin at the 
brain, and the structure was found to be the same. In these 
last mentioned nerves, the interstices between the fasciculi were 
smaller than in the optic nerve, rendering their transverse 
C 2 
