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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 127

In my measurements I have fixed the limits of the posterior horizontal
limb very much in the same way as Eberstaller. I have adopted the
same posterior limit, but in front I have always measured from the
" Sylvian Point." The origin of the single anterior limb of the Sylvian
fissure, when this exists alone, and of the anterior horizontal limb, when the
two front rami are present, cannot be relied upon as giving us, in every
case, precisely the same point. In calculating the relative length of the
fissure from the absolute measurement, I have reckoned the lateral length
of the hemisphere as being equal to one hundred: a length index for the
Sylvian fissure is thus obtained. The following Table gives these indices
for the two sides of the human brain at different periods of growth : —

Length Index of the Sylvian Fissure at different Periods of Growth and

on the two Sides.

Lateral Length of Hemisphere = 100.

Number of Hemispheres
Examined.

Period of Growth.

General Index
for both sides.

Index for the
Eight Side.

Index for the
Left Side.

53 (28 right, 23 left), .

Adult,

26-1

24-4

28

6 (3 right, 3 left),

11 to 15 years,

25-8

25-8

25'8

7 (3 right, 4 left),

4 to 5 years,

24-5

22-7

26

8 (5 right, 3 left),

First year, .

25

23-2

26-1

11 (6 right, 5 left),

Full-time foetuses,

28-4

27-8

29-2

12 (6 right, 6 left),

7£ to 8£ mouths, .

28

27

29

By these figures Eberstaller's assertion that the left fissure of Sylvius
is longer than the right is borne out in the fullest manner, and it will be
seen that this distinction is not confined to the adult brain, but is evident
at all periods of growth. In the early stages, however, the difference is not
so marked, and it is in the adult brain that it attains its full accentuation.

We have seen that the insula on the left side is relatively longer than
the corresponding area on the right side, and the question, therefore,