1887.] Prof. D. J. Hamilton on the Cortex of the Brain. 525 
entering the body. I further found that the oblique preparations 
he employed had been cut in an entirely wrong direction, in a 
direction which was calculated to divide the crossed callosal fibres, 
instead of rendering them more apparent. As I have elsewhere 
stated, he has not followed the directions I have so explicitly 
given in various of my published papers, and hence it is useless to 
argue the point. If he will harden the human brain, or, say, that 
of a sheep, by the method I have recommended, and cut this per- 
pendicularly in an oblique antero-posterior direction, he will see 
what I have described. It is impossible, as I have already indicated, 
to trace individual axis-cylinders throughout their entire course, 
but the continuity of individual bundles between the corpus callosum 
and the capsules can be demonstrated with facility. The difficulty 
of tracing the course of the crossed callosal fibres rests in this, that 
those which lie anteriorly after crossing run obliquely backwards , 
ivhile those which lie posteriorly run obliquely forwards , the point 
to which they all tend to converge being the knee of the inner 
capsule. 
It consequently happens that in whatever plane the organ may 
be cut, the fibres w T ill be divided at some point. In a completely 
transverse perpendicular section the crossed callosal fibres are 
usually divided, and being represented only by small fragments, are 
very apt to be overlooked in the dense mass of nerve-medulla lying 
in their neighbourhood. 
The Cortical Plexuses. — Of late years a good deal has been 
written of the most interesting plexus of medullated fibres which 
exists in the cortex of the cerebellum and cerebrum, by Exner 
(Sitzungsb. d. k. Akademie d. Wissensch., vol. Ixxxiii. Ab. iii., 
Eeb. 1881), Butzke (Arch. f. Psychiatrie, vol. iii., 1872), Gerlach 
(Centralb. f. d. med. Wissensch ., 1872, p. 273), Boll (Arch. f. 
Psychiatrie , vol. iv., 1874, p. 1), Bindfleisch (M. Schultze's Arch. f. 
mik. Anat., vol. viii. p. 453), and others. It seems likely, as Hill 
suggests, that since the discovery of these fine cortical plexuses our 
whole notions of what are known as nerve centres , and of the communi- 
cation that exists between nerve cells and fibres, will shortly be revolu- 
tionised. The plexuses to which I refer can be seen only when 
certain methods of staining are employed. Exner, who is generally 
regarded as having discovered the plexus in the cerebral cortex, 
