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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 229

the " Affenspalte " alone, whilst in the chimpanzee a branch is generally-
given off from the intraparietal, which turns up and joins this part of
the " Affenspalte," giving rise to the appearance of a terminal bifurcation
of the intraparietal sulcus. It would appear, therefore, that if the sulcus
transversus has any relation to the " Affenspalte " it is only in its upper part.

The chief evidence, and I might almost say the only phylogenetic
evidence, of the view which is generally entertained regarding the identity
of the sulcus transversus occipitalis of Ecker and the u Affenspalte " is
obtained from such forms as the white-crowned mangaby (Cercocebus
aethiops) (fig. 50). In the brain of this ape, and indeed in many others, the
intraparietal sulcus sends up the usual branch in front of the first annectant
gyrus. It then runs round its outer aspect, and, approaching the bottom of
the recess under the operculum, bifurcates into two branches which, in
diverging from each other, lose their identity in the bottom of the " Affenspalte
." The same condition may be seen in the orang-utan (fig. 37, p. 206),
and also occasionally in the chimpanzee (fig. 36, p. 204, right hemisphere).

Fig. 50.—The posterior part of the left hemisphere of the white crowned mangaby. a, parallel sulcus;

b, fissure of Sylvius ; c, intraparietal sulcus ; d, sulcus postcentrals superior ; e, descending
limb of the intraparietal sulcus ; /, upper end of parieto-occipital fissure turning outwards
on the upper surface of the hemisphere ; g, cut surface of occipital operculum.

Taken by itself this condition in these apes might be regarded as affording
presumptive evidence in favour of some kind of connexion between the sulcus
transversus occipitalis and the 11 Affenspalte" ; but in the face of the other
facts brought forward it proves very little.

I have tried to show that the phylogenetic evolution of the sulcus transversus
would seem to indicate that it is not an independent sulcus, but