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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 165

concealed within the fissure. On the other hand, at no time can one study
more satisfactorily the inferior transverse sulcus than in the two last
months of intra-uterine development. It is almost invariably present, and
it is almost always seen turning round the lower border of the operculum
below the lower end of the fissure of Eolando (PI. I., fig. 33, i. t.; PI. n.,
fig. 24; PI. iv., fig. 1, it).

I believe that where the union between the fissure of Rolando and the
inferior transverse sulcus takes place, it usually leads to a direct connexion
between the former and the fissure of Sylvius. In only four cases have I
seen the deep annectant gyrus crossing the bottom of the lower end of the
fissure of Rolando without such a connexion being established.

In the chimpanzee the deep annectant gyrus in the lower part of the
fissure of Rolando, which indicates a union with the inferior transverse
furrow, appears to be usually present. In only one out of four hemispheres
in my possession is it absent. In the other three it is strongly
marked, and in one of these there is a superficial connexion between the
fissure of Rolando and the fissure of Sylvius. Even in that hemisphere, in
which there is no trace of the deep annectant gyrus, it appears likely that
a fusion between the fissure of Rolando and the inferior transverse furrow
has taken place, because the sulcus is not any shorter and it reaches as low
down as in the case of the other hemispheres. The union, however, is of
a more complete kind.

In the orang, also, I find in two hemispheres a very distinct deep
annectant gyrus crossing the bottom of the inferior part of the fissure of
Rolando, and partially cutting off a small portion which probably represents
Eberstaller's inferior transverse furrow. When I deal with the
development of the fissure of Rolando I shall again have occasion to allude
to this deep annectant gyrus, and to point out its importance from a
morphological point of view.

But the inferior transverse furrow of Eberstaller is not confined to the
chimpanzee and the orang. It is also present in a well-marked form
in the baboon and the macaque; and in both of these forms it is often
split up into two distinct parts—an upper and a lower (fig. 33). This
gives us a key to a condition which is by no means uncommon in the