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Dk. Cunningham —Surface Anatomy of the Primate Cerebrum. 289

exhibited even more distinctly. Further, in many of the figures which I
have introduced for the purpose of illustrating the arrangement of the frontal
furrows (fig. 55, p. 251, and fig. 60, p. 268), the same conditions are depicted
. When the sagittal part of the inferior prsecentral furrow is typically
developed in the human cerebrum it is therefore evident: (l)that the hinder
end of the inferior frontal sulcus presents the same relations to it that the
sulcus rectus presents to the sulcus arcuatus (sulcus prsecentralis inferior)
in the lower apes; and (2) that the sulcus frontalis medius of the human
cerebrum lies more or less directly in the line of the sagittal part of the
inferior prsecentral sulcus. These relations are sufficient of themselves to
cause us to regard Eberstaller's assertion that the sulcus rectus of the ape
and sulcus frontalis medius of man are identical furrows, with grave
distrust.

But, as I have said, the phylogenetic and ontogenetic evidence also
points in a similar direction. The sulcus rectus shares with the sulcus
prsecentralis inferior an equal pre-eminence in the ape-cerebrum. It would
be difficult to say which presented the greater value from the morphological
point of view. They are both present (so far as I am aware) in the brains
of the great majority of the lower apes, and they exhibit a very nearly
equal depth. Turning now to the human foetal cerebrum, we recognize
the same pre-eminence in so far as their development is concerned. It is
true that the inferior prsecentral sulcus usually takes the lead, but it is
followed very closely by the inferior frontal furrow, and it is only in
exceptional cases that the sulcus frontalis medius appears before it.

The proof that is afforded by the chimpanzee cerebrum is still more
convincing. Eberstaller is perfectly right when he remarks that there are
great variations to be noticed in the arrangement of the frontal furrows in
different chimpanzee brains. One of the leading differences consists in
the presence or the absence of the sulcus frontalis medius. It is only in
the anthropoid brain that this sulcus first assumes a definite form. It
is true that in the cerebrum of the chacma baboon there are two small
transverse furrows developed in front of the sagittal limb of the inferior
prsecentral sulcus (fig. 66, p. 282, /. m.\ which may represent the first
traces of this sulcus in the apes, but upon this point I am by no means sure.

ROYAL IlilSH ACADEMY.-CUNNINGHAM MEMOIRS, NO. VII. [37]