1887.] Prof. D. J. Hamilton on the Cortex of the Brain. 523 
direction , however, the bundles of callosal nerve fibres can be traced 
from about the middle line continuously down to the outer and inner 
capsules , instead of upwards to the cortex as generally asserted . 
In PI. XV. fig. 2 I have given an accurate drawing of a section 
of the human brain ( x 10 diams.), stained and prepared by my 
modification of Weigert’s method, and taken from a region corre- 
sponding to the front of the basal ganglia. The parts of the 
preparation included in the drawing are the tectorial part of the 
corpus callosum (c.c.), the crossed callosal tract ( c.c.t .), the plexiform 
nucleus ( p.n.)f the head of the caudate nucleus ( c.n .), and the inner 
capsule (i.c.). The section from which the drawing was taken was 
made perpendicularly in the oblique antero-posterior direction just 
indicated. By so doing the continuity of a certain number of 
callosal fibres, as will be noticed, can be followed in a direction 
downwards, although it will be remarked that even here some of 
them (as at s.c.f.) have been obliquely divided. 
Prom the drawing it is evident that the bulk of the fibres issuing 
from the side of the tectorial part ( c.c .) of the corpus callosum 
sweep distinctly upwards, outwards, and downwards towards the 
inner capsule (i.c.). They are united in coarse bundles, and thus 
can be readily distinguished from those entering it (v.c.f. and p>.n.f.), 
which, although in bundles, are less condensed, and which, more- 
over, spread out in a radiate or fan-shaped manner. When the brain 
is cut in a perpendicular transverse direction the continuity of these 
fibres cannot be seen, because they have been severed by lying at 
an angle to the plane of section. Hence it is, I believe, that they 
have remained so long unnoticed. In no case have I been able to 
see a single bundle of fibres run upwards after emerging. After 
having crossed, the whole mass seems to turn downwards to the 
capsules, and to form the greater part of their bulk. 
In two late numbers of Brain (vols. viii. and ix.), Dr Beevor 
has taken exception to this view as originally enunciated by me 
in a communication to the Boyal Society ( Proceedings , No. 230, 
1884), and in papers which I subsequently published in the 
Journal of Anatomy and Physiology ( loc . cit.), in Brain (vol. viii., 
1886, p. 145), and elsewhere. He says that in the marmoset he has 
been unable to see the fibres turning downwards in the manner I 
* For description of this body see the sequel. 
