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338

Cunningham Memoirs.

of the hemisphere is taken from the frontal to the occipital poles, this
regarded as 100, and then the index calculated from the front.

In this and the next index the surface of the hemisphere was measured;
hence in the entire head the index would practically still apply, since the
errors due to variations in the thickness of the skull and scalp would not be
appreciably different in the observations.

Whereas the coincidence of the sulcus and suture is commoner at birth,
the advance forwards of the sutural line in subsequent years carries back
the position of the sulcus relative to the exterior.

By the employment of the indices given by Professor Cunningham on
p. 300 in the manner just indicated, the vertical stem of the sulcus may be
fixed with fair approach to accuracy. I have tested this on the cadaver.

(b) The focus of branching of the sulcus is a point of exceeding importance
from the fact that it, in both the lower and higher apes, marks the
separation of the representation of the conjugate deviation of the eyes from
the facial movements. To determine the position of this point which
marks a horizontal level, it was necessary to have a relative measurement
made on preparations of unquestionable exactitude. To obtain this I took
as a basis line easily capable of external measurement the distance from the
bregma to the centre of the external auditory meatus, and determined the
index for the distance on this line of the bregma from the bifurcation focus
of the praecentral sulcus (inferior). The measurements gave the following
indices:—

Age.

Sex.

Heads
Measured.

Bregma-Prsecen-
tral Index.



( Males,

4

40

Children up to 11 years,







( Females, .

3

40-6



( Males,

5

38-2

Adult, .





( Females, .

3

42-7

Although the number of heads available is relatively few, still the facts
obtained are so definite as to make it clear that the indices afford a good