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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 123

certain of the apes the index is still higher; thus in the mangaby, chimpanzee
, and hamadryas it varies from 36'2 to 37*2 :—

Relative Position of the " Sylvian Point " with reference to the Anterior

End of the Cerebrum in Man and the Ape.

Lateral Length of the Hemisphere = 100.



Number of
Hemispheres
Examined.

Fronto-Sylvian
Index.

European (Adult), ....

53

32-7

Negro, .....

5

34-5

Orang, .....

2

34-2

Cebus, .....

6

34-5

Cynocephalus, ....

7

34-4

Macaque, .....

5

34-5

Mangaby, .....

6

36-2

Chimpanzee, .....

4

36-4

Hamadryas, .....

2

37-2

I do not lay much stress upon the high fronto-Sylvian index obtained
for the five negro brains. As I have previously explained, the negro
brains in my possession were hardened on the west coast of Africa with
no special precautions for the preservation of the true form, and although
I have only measured those which appear to have suffered the least amount
of distortion, I cannot attach much importance to the results obtained.

But the position of the 11 Sylvian Point" varies somewhat in the human
brain at different periods of growth. It makes a slight advance forwards as
growth progresses, and it may be said to become finally fixed in its position
between the fifth and the eleventh year. The following Table makes this
clear :—

[16*]