(with the exception of the sylvian depression), and they project
backwards far beyond the cerebellum.

2. The sulci, properly so called, begin to appear in the
interval between the end of the fourth and the beginning of the
sixth month of foetal life, but Ecker is careful to point out
that, not only the time, but the order, of their appearance is
subject to considerable individual variation. In no case,
however, are either the frontal or the temporal sulci the
earliest.

The first which appears, in fact, lies on the inner face of the
hemisphere (whence doubtless Gratiolet, who does not seem to have
examined that face in his foetus, overlooked it), and is either
the internal perpendicular (occipito-parietal), or the calcarine
sulcus, these two being close together and eventually running
into one another. As a rule the occipito-parietal is the earlier
of the two.

3. At the latter part of this period, another sulcus, the
"posterio-parietal," or "Fissure of Rolando" is developed, and it
is followed, in the course of the sixth month, by the other
principal sulci of the frontal, parietal, temporal and occipital
lobes. There is, however, no clear evidence that one of these
constantly appears before the other; and it is remarkable that,
in the brain at the period described and figured by Ecker (loc.
cit. pp. 212-213, Taf. II, figs. 1, 2, 3, 4), the antero-temporal
sulcus (scissure parallele) so characteristic of the ape's brain,
is as well, if not better developed than the fissure of Rolando,
and is much more marked than the proper frontal sulci.