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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 269

principally in the anterior-posterior direction, but often terminating at their
posterior extremities by a more or less transverse branch (incisure en T
ou en L). In the most ordinary type there are three distinct longitudinal
furrows." He then goes on to say that two of these may unite so as to
subdivide the superior frontal convolution into two tiers.* It was the
presence of these sulci that led Benediktf to believe that the two uppermost
" Urwindungen " of the carnivore brain were in man fused into one,
and represented by the superior frontal convolution.

These sulci are present in a more or less prominent fashion in all European
brains, and as they effect a partial subdivision of the first frontal
convolution into a mesial and an external portion, I purpose grouping them
under the name of sulcus frontalis mesialis. Associated with them, and
lying in direct series with them, we note the sulcus prsecentralis marginalis
to which we have already alluded (p. 258).

There is not a trace of the sulcus frontalis mesialis in the anthropoid
apes. It therefore constitutes a group of sulci peculiar to the human brain.
Further, it would appear that these furrows are feebly developed or even
absent in the negro cerebrum. In three out of seven negro hemispheres I
could not detect any sign of the sulcus frontalis mesialis; whilst in one
only did it attain a development at all comparable with that usually
observed in the European.

But it is by no means uncommon to find the different factors of the
sulcus frontalis mesialis running into each other so as to produce a long
continuous furrow completely dividing the superior frontal convolution into
two tiers (vide figs. 57 and 59, pp. 259 and 262). When this is the case
I have noticed that there is a decided tendency for the sulcus frontalis
medius to link itself on to the first frontal sulcus. A complete division of
the superior frontal convolution is thus usually associated with an imperfect
subdivision of the middle frontal convolution, and vice versa. This is
well seen in the two figures referred to. In short, all the evidence goes to
prove that the sulcus frontalis medius, with the sulcus frontalis mesialis,

* Description elernentaire des circonvolutions cerebrales de l'homme.—Memoires sur le cerveau
de l'bomme et des primates, par Paul Broca, publies par le Docteur S. Pozzi. Paris, p. 788.
f Anatomische studien an Verbrecher Gebirnen. Epilogomena m., p. 133. Wien, 1879.