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62

Cunningham Memoirs.

Human Brain.

Lambdo-parieto-occipital Indices—Mesial length of the Hemisphere taken as 100—The
Indices express the relative distance of the fissure in front of the Lambda.

Period of Growth.

Average
Index for
both Sexes
and both
Hemispheres.

Average
Index for
Males.

Average
Index for
Females.

Average
Index for
right side.

Average
Index for
left side.

Adults, ....

2-9

2-6

3-7

3-6

1-8

11 to 15 years,

0-9

0-5

1-8

1-4

0-4

4 to 5 years ....

4-5

3-8

6-2

3-6

5-4

First year of life, .

4-8

8-7

4

5'2

4

Full-time foetuses,

4

3-9

45

3-6

4-5

Foetuses—7^ to 8£ months, .

4-9

5-5

3'8

4-8

5-1

Foetuses—6£ to 7£ months, .

5-9









From these indices it is apparent that the relative position of the fissure
with reference to the lambda is subject to a certain amount of variation.
From the eighth month of foetal life up to the fifth year of childhood the
relation of the fissure to the lambda remains virtually the same. The index
varies from 4 to 4*9. In foetuses younger than this the distance between
the lambda and the fissure is distinctly greater; and by examining
the Table in page 57, in which the occipital indices are given, it will be
seen that the reduction of the distance between the two points cannot
altogether be explained by the changes which take place in the position
of the fissure on the upper border of the hemisphere. It can only be
accounted for by supposing likewise a slight forward movement of the
lambda as the eighth month of intra-uterine life is approached.
Again, from the eleventh year up to adult life, the distance between
the lambda is very considerably reduced. In this case it would appear
that the change is produced by a change in the position of the lambda,
the fissure remaining more or less stationary. A study of the occipital
indices will show that this explanation of the changing relations is