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190

Cunningham Memoirs.

in this direction. An}^one who studies the average cephalic indices which
I have introduced into the Table will see that the angle increases and
decreases with the rise and fall of the cephalic index.* In brachycephalic
heads the angle is more open than in dolichocephalic heads. In the first
twelve months of extrauterine life all the specimens I examined were from
females. Collectively they present the average angle of 70o,6, but if we
analyze the various items which go to form the whole, we find three
hemispheres with an average angle of 67°• 7, and the unusually low cephalic
index of 71, whereas the others gave an average angle of 73° and an
average cephalic index of 79.

It is right to state that the results obtained by Mr. Hare do not coincide
with this view, and from the fact of his measurements having been made
upon the brain in situ I attach a high importance to them. In five dolichocephalic
heads the average angle was 68°"6, whilst in six brachycephalic
heads it was 66°*6.

VIII. Length of the Fissure of Rolando.—Passet has endeavoured to
prove that the fissure of Rolando is both relatively and absolutely longer
in the male than in the female, and Rohon believes that the same sexual
distinctions may be detected in the chimpanzee. The absolute length of
the fissure is of no importance, because this will vary with the absolute size
of the brain, and therefore the increase in length in the male is what might
naturally be expected. In order to get at the relative length, it is necessary
to have some standard wherewith we may compare it. As the most convenient
standard I have taken the total length of the hemisphere measured
by the tape along its superior border. This we shall regard as being equal
to 100. The fissure was measured by a thread introduced between the lips
of the fissure and following accurately all its flexures.

My results are very different from those obtained by Passet. It appears
to me that three circumstances affect the length of the fissure:—(1) the

* Welcker, Broca, and Calori hold that the head of the female is more dolichocephalic than
that of the male. If this he the case, we would expect to find a more acute Eolandic angle.
Weisbach, Arnold, and Mantegazzi, on the other hand, consider that it is the male head that
shows the greatest amount of dolichocephaly.