On the Brain | Page 7

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
"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.
Taking the facts as they now stand, it appears to me that the order of
the appearance of the sulci and gyri in the foetal human brain is in
perfect harmony with the general doctrine of evolution, and with the
view that man has been evolved from some ape-like form; though there
can be no doubt that form was, in many respects, different from any
member of the Primates now living.
Von Baer taught us, half a century ago, that, in the course of their
development, allied animals put on at first, the characters of the greater
groups to which they belong, and, by degrees, assume those which
restrict them within the limits of their family, genus, and species; and
he proved, at the same time, that no developmental stage of a higher
animal is precisely similar to the adult condition of any lower animal. It
is quite correct to say that a frog passes through the condition of a fish,
inasmuch as at one period of its life the tadpole has all the characters of
a fish, and if it went no further, would have to be grouped among fishes.
But it is equally true that a tadpole is very different from any known
fish.
In like manner, the brain of a human foetus, at the fifth month, may
correctly be said to be, not only the brain of an ape, but that of an
Arctopithecine or marmoset-like ape; for its hemispheres, with their
great posterior lobster, and with no sulci but the sylvian and the
calcarine, present the characteristics found only in the group of the
Arctopithecine Primates. But it is equally true, as Gratiolet remarks,
that, in its widely open sylvian fissure, it differs from the brain of any
actual marmoset. No doubt it would be much more similar to the brain
of an advanced foetus of a marmoset. But we know nothing whatever
of the development of the brain in the marmosets. In the Platyrrhini

proper, the only observation with which I am acquainted is due to
Pansch, who found in the brain of a foetal Cebus Apella, in addition to
the sylvian fissure and the deep calcarine fissure, only a very shallow
antero-temporal fissure (scissure parallele of Gratiolet).
Now this fact, taken together with the circumstance that the
antero-temporal sulcus is present in such Platyrrhini as the Saimiri,
which present mere traces of sulci on the anterior half of the exterior of
the cerebral