ON THE BRAINS OF TWO IDIOTS OF EUROPEAN DESCENT. 
521 
Bushwoman of a square inch, whilst in the European it amounts to an< ^ i n 
the Chimpanzee to of a square inch. Compared with the area of the internal sur- 
face of one hemisphere, the sectional area of the corpus callosum is in the Bush- 
woman’s brain as 1 to 25, in the European as 1 to 12'5, and in the Chimpanzee as 1 to 
28-5 ; so that the corpus callosum, thus estimated in proportion to the cerebrum, is in the 
Bushwoman only half as large as in the European, and not much larger proportionally than 
in the Chimpanzee. The anterior commissure (a) is also singularly small ; the posterior 
commissure is very slender ; whilst (probably an individual peculiarity only) there is no 
trace of the so-called soft commissure. On the whole, therefore, the system of transverse 
commissural fibres is defective ; and as the size of the medulla oblongata, in proportion 
to the unusually narrow cerebrum, is larger even than in the European (so that the 
radiating system is probably not so much diminished), it would seem as if the relative 
deficiency of white substance within the hemispheres was owing in a great degree to the 
fewness of the transverse, as well, perhaps, as of other commissural systems of fibres. I have 
elsewhere pointed out the same condition in the Chimpanzee’s brain ; and it doubtless 
is associated, in the Bushwoman’s brain, with its inferior bulk and less convoluted sur- 
face. The proportional size of the corpus callosum, thus considered, offers, I believe, a 
not inconvenient test of the relative perfection of any given normal brain of certain plan. 
Comparative anatomy supports this view. Of the longitudinal system of commissures, 
the fornix is thin, the taenia semicircularis slender, and the striae longitudinales plainly 
visible. 
The septum lucidum, with its intervening ventricle, is large, both in depth and extent 
from before backwards. The lateral ventricle in the left hemisphere (Plate XIX. fig. 6) 
proved to be a very large cavity; the body ( a ) measured 1*5 inch in length, the anterior 
cornu (h) between ’6 and *7, the posterior cornu (c) 1*8, the descending cornu ( d ) 1*5 ; 
the corresponding numbers in an ordinary example of a European brain were 2*1, 1*4, 
1*2, and 2*6. Comparing these dimensions with the total lengths of the two cerebra 
respectively, viz. 5’ 8 inches for the Bushwoman, and 6 '5 for the European, we get the 
following proportions: -25, *11, *31, and *43 to 1 in the Bushwoman, and in the Euro- 
pean ‘32, *21, T84, and *4 to 1. In the former, therefore, the body is short, the ante- 
rior cornu very short, the descending cornu long, and the posterior cornu very long, the 
proportion being as 5 to 3. The width and depth of the posterior cornu are as remark- 
able as its length; the width varies from ’3 of an inch, opposite the projection of the 
hippocampus minor, to upwards of *4 in the wide recess behind that eminence ; the 
depth of the cornua at its deepest part, is *4 of an inch. From the end of the posterior 
cornu to the extremity of the occipital lobe is *5 of an inch, that is, a little more than 
-jQ-th of the total length of the brain, showing an unusual proximity of the posterior 
cornu to the apex of the posterior lobe. The hippocampus major ( e ) is narrow, it 
expands at its lower end, on the anterior border of which is a single prominence, but 
otherwise there is no trace of indentation. The hippocampus minor (f ) is of large 
dimensions, projecting boldly into the middle of the posterior cornu, and subsiding 
