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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 141

figs. 13 and 14, the fissure is immediately subjacent to the fore-part of the
suture; in figs. 12 and 16 it is above the suture ; whilst in figs. 15 and 17
it is below the suture. The female head represented in fig. 15 exhibits a
very extreme case of depression of the Sylvian fissure, and at the same time
a very high squamous arch. The index was as high as 6-7. For many
years before death this subject had been insane.

The above Table shows that the relative position of the Sylvian fissure
with reference to the squamous suture is subject to considerable variation.
We may conclude that it is equally common to find it above, below, or
immediately subjacent to the fore-part of the suture.

I next give a Table which brings out the relation of the fissure to
the suture in the foetus, and in children. In this group I also include a
youth of fifteen years old. In all of these the fissure was found above the
level of the anterior part of the suture.

Relative Position of the Fissure of Sylvius with reference to the Squamous

Suture in the Foetus and Child.

Temporo-parietal Depth = 100.

Period of Growth.

Number
of Hemi-

sphei-es
Examined.

Sylvio-

Squarnous
Index.

Male.

Sylvio-Squa
Female.

mous Index.
Eight.

Left.

7i to 8 months' foetus, ....

4

24

26-1

23-3

25-3

19-1

Full-time foetuses (fig. 3, PI. v.), .

6

20-3

19-5

21-1

19-6

21-7

First year of childhood (figs. 4, 5, PI. t.),

3

13-6

14-8

13

136



4 to 5 years (figs. 6, 7, and 8, PI. vi.), .

5

65

8-7

33

7-1

58

Girl, 11 years old (fig. 9, PI. vi.), .

2

2-7



2-7

2-3

CO

Boy, 12£ years old (fig. 10, PI. vi.),

1

3-4

3-4



3-4



Youth, 15 years old (fig. 11, PI. yn.), .

2

3-6

3-6



2-1

5-2

The posterior limb of the Sylvian fissure is thus seen to be relatively
most distant from the squamous suture at the time when it is first formed
by the apposition of the lips of the upper and lower opercula of the Sylvian