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De. Cunningham—Surface Anatomy of the Primate Cerebrum. 109

Relative Length of the Island of Reil in the Adult Brain in the two Sexes.

Lateral Length of Hemisphere = 100.

Number of Hemispheres
Examined.

Fronto-Central Index.

Central Index.

Occipito-Central Index.

Males.

Females.

Males.

Females.

Males.

Females.

Males.

Females.

14

11

25-3

27-8

30-3

28-4

44-3

43-7

My own impression is that the difference between the two sexes is in this
Table more accentuated than^it is in reality, and that had I examined a
larger number of hemispheres it would, in all probability, have been somewhat
lessened.

The figures which I have obtained, however, in connexion with my
comparison of the right and left hemispheres, renders it probable that at
all periods of life there is a relatively greater development of the island of
Reil on the left side than on the right. The following Table shows this:—

Relative Length of the Island of Reil in the Right and Left Hemisphere.

Lateral Length of Cerebrum = 100.

Period of Development.

No. of Hemispheres
Examined.

Fronto-Central
Index.

Central Index.

Oceipito-Central
Index.

Eight.

Left.

Eight.

Left.

Eight.

Left.

Eight.

Left.

4^ to 5 months,

3

2

28-1

24-5

22-8

24-4

49-1

51-1

5 to 5^- months,

5

5

25-8

25-7

23-8

24-8

50-4

49-5

5^ to 6 months,

5

6

25-9

25-5

25-8

25-9

48-3

48-6

6 to 6-1- months,

5

4

26-1

26-5

26-1

26-4

47-8

47-1

6£ to 7£ months, .

2

1

26-2

26-1

28-4

27-2

45-4

46-7

7-k to 8^ months, .

6

6

26-4

26-5

28-4

29

45-3

44-4

Eull-time foetus, .

6

5

24-6

23-9

3L6

32-5

43-8

43-6

First 12 months, .

5

3

26-6

23

28-1

33-2

45-3

43-8

4 to 5 years,

3

4

27-1

27-1

30

27-9

42-9

45

11 to 12 years, .

2

3

27-2

26-6

29

29-1

43-6

44-3

Adults,

16

12

26-5

25-9

29'2

30-1

44-3

44