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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 275

The upper part of the inferior prsecentral sulcus is bent forwards to
form the anterior part of the ramus horizontals, but the posterior part is
absent. A well-marked middle prsecentral furrow is evident, and in such
a position that the idea is suggested that it may possibly represent the
detached posterior part of the horizontal ramus of the inferior prsecentral
sulcus.

The inferior or second frontal sulcus appears simultaneously with, or
immediately after, the sulcus prsecentralis inferior. As a rule, it becomes
evident about the end of the sixth month, although in some cases it may
be seen earlier (vide PI. n., fig. 14). It is generally composed, in the first
instance, of two pieces, an anterior and a posterior, which ultimately run
into each other (PI. i., fig. 25 ; and PI. n., figs. 14 and 20). As we have
observed, the point of union of these two pieces is frequently indicated in
the adult brain by the presence of a deep annectant gyrus, whilst a failure
in their junction leads to the retention of this bridging convolution on the
surface. In figure 19 (PI. u.) it will be noticed that the two portions of
the furrow are exhibited in the form of two pit-like depressions, which are
united by a shallow furrow over an intervening eminence.

The hinder or basal part of the inferior frontal sulcus may be developed
in direct connexion with the sulcus praecentralis inferior, and when this is
the case it is often extremely difficult to distinguish it from the ramus
horizontalis—more especially in those cases where the latter is poorly
developed or not yet formed. As an example of this I may call attention
to a cerebrum figured in Plate n. (fig. 24). The strongly-marked sagittal
branch which proceeds forwards from the vertical stem of the inferior prsecentral
sulcus presents a striking similarity to the ramus horizontalis as it
is seen in its typical F-shaped form in a lower ape. Notwithstanding this
there cannot be a doubt but that it is in reality the basal or hinder part of
the second frontal sulcus. The ramus horizontalis in this specimen is
very feebly marked. It is represented by a weak bifurcation at the upper
extremity of the vertical stem.

Another case which presents similar elements of difficulty is seen in the
annexed figure (fig. 63, p. 276). The basal portion of the inferior frontal
sulcus is a long oblique furrow, in direct continuity with the vertical

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