1887.] Prof. D. J. Hamilton on the Cortex of the Brain. 533 
which this nucleus is placed in continuity with the opposite cerebral 
cortex. 
The arrangement seems a probable one ; all the most important 
motor and sensory channels seem to cross the middle line at some 
point. We see this exemplified in its most simple form in the 
ordinary ascending and descending paths in the spinal cord ; and 
there seems good reason for believing that the same type of con- 
struction prevails higher up. The callosal fibres would thus 
represent the decussation of the multiform tracts which do not cross 
in any of the commissures or decussations lower down. The greater 
number of them are probably not motor nor purely sensory in their 
function, but in great part educational. They are, in fact, the 
means of impressing the opposite cortical centres with the stimuli 
that have been made upon the intermediate centres lower down. 
Explanation of Plates XIV., XV. 
Fig. 1. Perpendicular opaque transverse section through the region of 
the infundibulum of human brain hardened by injecting Midler’s fluid. 
"Natural size. In the centre is the corpus callosum, and at each side of 
it, turning upwards, outwards, and downwards in the centrum ovale to the 
two capsules, is the arched mass of fibres which I have named the crossed 
callosal tract. The fibres coming in to the corpus callosum from the cortex 
of the vertex and elsewhere are seen interlacing with the fibres of this 
arched mass. The drawing was made with the greatest care, and may be 
taken as being as nearly as possible a facsimile of the preparation from 
which it was copied. The brain, after being thoroughly hardened, was 
simply cut into segments about half an inch thick, whose surfaces were 
polished in the freezing microtome. Nothing further was done to it. 
The drawing represents the surface of one of these segments. 
Fig. 2. Perpendicular oblique antero-posterior section of human brain 
through the corpus callosum and crossed callosal tract, x 10-20 diams. 
Stained by the author’s modification of Weigert’s copper-heematoxylene 
process, c.c., corpus callosum ; c.c.t. : crossed callosal tract ; v.c.f., v.c.f, 
callosal fibres from the vertex ; p.n.f. , p.n.f, same, from cortex lower down, 
running towards the plexiform nucleus (p.n .) ; d.f, direct cortical fibres 
lying outside the crossed callosal tract, and running down to the inner 
capsule ( i.c .); s.c.f., severed callosal fibres of the crossed callosal tract; 
c.n., caudate nucleus ; x ., part of preparation from which figure 3 was 
drawn. 
Fig. 3. Portion of white matter immediately under the grey mantle of 
the cortex at the vertex in the motor region. Stained as in figure 2. 
x 300 diams. a., a., bundles of large medullated fibres passing downwards 
from the grey matter ; b., a clot in a blood-vessel ; c., the granular neur- 
oglia ; d., the felt-like plexus of nerve fibres surrounding the straight 
bundles coming from the cortex. 
