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238

Cunningham Memoirs.

the anthropoid apes that the sagittal portion of the intraparietal furrow
assumes the most distinctly sagittal direction; (5) and, finally, I agree with
Eberstaller in considering that it is the inferior parietal lobule which
shows a relative increase in size in the evolution of the parietal lobe, and
not the superior parietal lobule. It is necessary, however, that I should
bring forward the evidence upon which these assertions are based.

Relative size of the arcus parieto-occipitalis.—I have measured this gyrus,
from the mesial plane to the highest point of its convexity, in twenty-
eight adult human hemispheres, in twenty-three human foetal hemispheres
, varying in development from the eighth month up to the full
period, and in eight anthropoid hemispheres. The results I obtained are
contained in the following Table :—

Relative size of the Arcus Parieto-Occipitalis.

Mesial Length of the Cerebrum being reckoned as 100.



Male.

Female.



Number
of Hemispheres
.

Index.

Number
of Hemispheres
.

Index.

Adult human brain, ......

15

11

13

11-2

Foetal human brain (from eighth month to full-time),

9

9-3

14

10-6

Chimpanzee brain,......





4

16-2

Orang-utan brain,......

4

16-9





In the adult human brain there is, therefore, virtually no sexual difference
to be detected in the relative size of the arcus parieto-occipitalis. In
the foetal brains, however, we note that in the female the relative size of this
gyrus is greater (index 10-6) than it is in the male (index 9*3). But the
most striking point brought out by this Table is the great relative size of
the gyrus in the chimpanzee and the orang. Eberstaller has, in a measure,