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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 287

direction of the furrow in the human brain. But whether this explanation
is right or wrong, I do not consider that much weight should be ascribed
to a slight difference of inclination in the determination of so important
a homological question. I may further add that in many cases the inferior
frontal furrow, in its early stages of development in the human cerebrum,
presents a direction similar to that of the sulcus rectus in the lower apes
(fig. 62, p. 274). Indeed the general tendency of the frontal furrows,
both in the apes and in the early stages of their existence in the human
foetus, is to assume an oblique and not an accurately sagittal direction.
We see this not only in the sulcus rectus or inferior frontal furrow, but
also in the several pieces which go to form the first frontal sulcus—all
tend by their anterior ends somewhat towards the mesial border.

With regard to the second argument advanced by Eberstaller, I may as
well at once state that my views regarding the u anterior angle of the
Sylvian region," and the so-called anterior limb of the Sylvian fissure in the
apes, are altogether different from those which are usually accepted, and
are more in accordance with those which have been advocated by Pansch
and Kohlbriigge. At a later stage I hope to be able to establish my position
in this respect. If I do so, Eberstaller's contention falls to the
ground.

The evidence in favour of regarding the sulcus rectus in the cerebrum
of the lower apes the homologue of the sulcus frontalis inferior in the
cerebrum of man is derived from the following circumstances:—

1. The position of the sulcus in relation to the sulcus arcuatus or
inferior praecentral furrow in the apes and in man.

2. Its early development in the human cerebrum.

3. The presence in many cases in the cerebrum of the chimpanzee of
a true sulcus frontalis medius, in addition to the sulcus rectus or inferior
frontal sulcus.

In the brain of the lower apes, one of the most conspicuous features of
the sulcus rectus is the position of its hinder end below the level of the horizontal
limb, and close to the vertical stem of the sulcus prsecentralis iuferior
{vide the sketches of the cerebrum of Cebus, Callithrix, and the chacma
baboon, rigs. 6-i, 65, 66, pp. 280-282). In the human cerebrum, when the