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Cunningham Memoirs.

it was also present. It is therefore not so constant in these apes as the
corresponding element of the Rolandic fissure (p. 165).

Turning next to the anthropoid apes we find that in the chimpanzee
and orang, Eberstaller's lower element of the postcentral sulcus is almost
invariably present. In six hemispheres of the former and in four hemispheres
of the latter it was very evident in every case. Further, it is not
uncommon to find it composed of two small sulci—one placed above the
other. When this occurs the uj3per piece may be united superficially with
the sulcus postcentralis inferior—a distinct deep annectant gyrus marking
the place of junction—whilst the lower piece may turn round the margin of
the fronto-parietal operculum, and open into the Sylvian fissure. The same
condition is occasionally seen in the macaque and baboon. Waldeyer*
assures us, however, that Eberstaller's lower element of the postcentral
sulcus is absent in the gibbon.

The ramus occipitalis of the intraparietal sulcus, as it is seen in the apes,
presents some features of special interest; but it is better to defer the study
of these until we deal with the corresponding segment of the fissure in the
human brain.

Before turning from the intraparietal sulcus in the apes, we may as well
point out that in Cebus, the baboon, and macaque, it is at least twice as
deep as the fissure of Rolando. The latter furrow is, comparatively
speaking, shallow. In the chimpanzee and the orang the difference in
depth between these two sulci is not nearly so marked, although it is still
very manifest that the intraparietal furrow is the deeper of the two. In
the human brain the position of affairs is reversed, because although the
intraparietal sulcus cannot be said to have lost anything in so far as its
relative depth is concerned, the fissure of Rolando, in the great majority of
cases, cuts more deeply into the cerebral surface. This is an interesting
point in connexion with the law which Pansch so strenuously advocated,
and which we shall give in his own words : " Die Vertiefung der Furchen
im Laufe der Entwicklung findet im Allgemeinen ziemlich gleichmassig bei
alien Furchen statt. Die zuletzt auftretenden Furchen bleiben stets flach,

* Das Gibbon-Hirn, Virchow's Festschrift. Band i., 1891.