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Cunningham Memoirs.

(PI. iv., fig. 1, «. jp.), and in those cases where it joins the sulcus postcentrals
inferior above, and turns round the opercular border below, it brings
about a junction between the intraparietal sulcus and the Sylvian fissure.
This confluence occurred in about 25 per cent, of the adult hemispheres
examined, but in every case the point of union with the sulcus postcentralis
inferior was indicated by the presence of a deep annectant gyrus.

III. Intraparietal Sulcus in the Apes.—The morphological importance
of the different elements of the intraparietal sulcus can best be appreciated
by an appeal to the brain of the apes. By this means we can accord to each
its proper value.

In the great majority of the lower apes the most apparent part of the
intraparietal sulcus is present in the form of a sharply-cut oblique fissure,
which traverses the parietal lobe from its antero-inferior angle to its
postero-superior angle. Here it bends round the upper part of the angular
convolution, and comes to an end. Its mode of termination differs considerably
in different members of the group, and will be studied more fully
in another part of this chapter. This continuous fissure represents the
sulcus postcentralis inferior, the ramus horizontalis, and the ramus occipitalis
of the human brain.

The sulcus postcentralis superior is in many apes, as for example, Cebus
capucinus and Cebus albifrons, entirely unrepresented. In nine cerebral
hemispheres taken from these two species, I could not detect the slightest
trace of this furrow. In the baboon, the macaque, and many other old-
world apes, it is invariably present. It may take the form of a stellate
depression behind the upper part of the fissure of Rolando, or it may be
present in the shape of a shallow linear furrow. Both conditions are met
within the baboon (fig. 47, e., p. 224, also PI. iv., fig. 8); and in three of the
fourteen hemispheres taken from this form which I have before me, the
sulcus postcentralis superior extends downwards, and effects a junction
with the main part of the fissure, thereby indicating a subdivision of the
latter into two portions corresponding to the ramus horizontalis and the
sulcus postcentralis inferior of the human cerebrum (PI. iv., fig. 8, p.1 and
p.2). In the macaque it is more usual for the sulcus postcentralis superior