fissure (antero-temporal) on the posterior half of the face of the
hemisphere is more marked than any of those vaguely indicated in the
anterior half. If the figure is correct, it in no way justifies
Gratiolet s conclusion: Il y a donc entre ces cerveaux [those of a
Callithrix and of a Gibbon] et celui du foetus humain une difference
fondamental. Chez celui-ci, longtemps avant que les plis temporaux
apparaissent, les plis frontaux, ESSAYENT d exister.
Since Gratiolet s time, however, the development of the gyri and sulci
of the brain has been made the subject of renewed investigation by
Schmidt, Bischoff, Pansch (78. Ueber die typische Anordnung der
Furchen und Windungen auf den Grosshirn-Hemispharen des Menschen und
der Affen, Archiv fur Anthropologie, iii. 1868.), and more
particularly by Ecker (79. Zur Entwicklungs Geschichte der Furchen und
Windungen der Grosshirn-Hemispharen im Foetus des Menschen, Archiv
fur Anthropologie, iii. 1868.), whose work is not only the latest, but
by far the most complete, memoir on the subject.
The final results of their inquiries may be summed up as follows: 1.
In the human foetus, the sylvian fissure is formed in the course of the
third month of uterogestation. In this, and in the fourth month, the
cerebral hemispheres are smooth and rounded (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
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