340 Proceedings of Royal Society of Edinhurgh. [may 7, 
the corpus callosum, which has succeeded in growing so far toward 
the middle line. Von Gudden’s law of the complete atrophy of a 
divided embryonic system seems to decide against this view. 
The view of Professor Hamilton of Aberdeen, with regard to the 
distribution of the callosal fibres, seems to be completely negatived 
by the appearance in my case and in those recorded by Onufrowicz 
and Kaufmann. It is obvious that if, in the normal brain, the corpus 
callosum is the main constituent of the internal capsule, that the latter 
structure should almost disappear when the corpus callosum is absent. 
This, however, does not occur. In my case it was not possible to 
detect any abnormality in it ; and Onufrowicz and Kaufmann make 
similar statements. Hamilton {Proc. Roy. Soc.^ 1887) endeavours to 
explain this by the theory, that the corpus callosum is present, 
but does not decussate — that it ascends to the cortex of the same 
hemisphere. Were that so the normal appearance of the tapetum 
should be present in the occipital lobe in my case. It is unquestion- 
ably absent. Further, in Kuxton’s case, fig. II, where the anterior 
part of the corpus callosum is atrophied completely, sections taken at 
all levels show that the internal capsule is not in the least diminished. 
Euxton’s case further serves to explain the apparent curving 
downwards of the corpus callosum into the internal capsule. The 
arched fibres remain though the corpus callosum is gone, but 
they are seen, on naked eye and microscopic examination, to come 
in very great measure from the gyrus fornicatus. It is no doubt 
the intermingling of the callosal and capsular systems that produces 
the appearance that has misled Hamilton. As further evidence of 
the separateness of those two systems may be mentioned the fact 
that, in the mature human foetus and infant up to three months, the 
callosal system is non-medullated; while in the mature foetus the 
whole posterior limb, and in the three months’ child almost the whole 
of both limbs, of the internal capsule are medullated. And further, 
in some of the lower mammalia the strand from the capsule to the 
gyrus fornicatus can be traced as quite distinct from the callosal 
system. 
Lastly, the case is instructive with regard to the supposed 
functions of the corpus callosum. A great deal has been written as 
to its supposed function of co-ordinating the corresponding convolu- 
tions of the opposite hemispheres — a view which seems to date from 
