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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 215

On the Continent it is usual to describe this variety of the intraparietal
sulcus as the normal arrangement ;* and in the numerous memoirs in which
the cerebral hemispheres have been drawn from nature, it will generally be
observed to be the condition depicted. It is interesting to note that the
chimpanzee, gibbon, and in some cases the baboon and other apes, exhibit
a similar disposition of the three rami of the intraparietal sulcus.

Fis. 42.—Posterior part of the left hemisphere of an elderly female. The more usual
condition of the intraparietal sulcus is exhibited.

Variety V.—Ramus horizontalis apparently joined to the lower end of the
upper part of the postcentral sulcus ; loiver part of the postcentral sidcus separate
(fig. 43).—This is a very rare form of the intraparietal sulcus. It was
noted in only two adult hemispheres and in one hemisphere from a
child.

The condition in this variety of sulcus is easily explained if we bear in
mind that it is not unusual for the sulcus postcentralis inferior to develop
in two pieces which ultimately run into each other. In the abnormal
arrangement under consideration the upper piece of this furrow has become
confluent with the ramus horizontalis as usual, and also with the sulcus
postcentralis superior, but it has failed to unite with the lower piece. The
variety therefore can hardly be described as one in which the ramus horizontalis
has become connected with the sulcus postcentralis superior, seeing
that it only does so through the intermediation of the upper end of the

* For example, see Schwalbe's work on " Neurologie," p. 551, and Gregenbaur's " Text-book
of Anatomy," p. 842, vol. ii., 3rd edition.