Freiburger historische Bestände - digital

286

Cunningham Memoirs.

orang; and Kohlbriigge * states that it occurs amongst the lower apes only
in one form, viz. in Cynocephalus porcarius. In both Callithrix and the
chacma baboon there seems to be a tendency to its formation; but I am
not prepared to insist that in these cases the furrow which I have marked
p. c. s. is the representative of the sulcus praecentralis superior (fig. 65,
p. 281, and fig. 66, p. 282); and perhaps in marking the furrow p. c.s. in
the drawings alluded to, my judgment has been somewhat biassed by the
fact that in the human foetal brain the furrow in question appears to be
more firmly established than the sulcus frontalis superior.

The sulcus rectus in the lower apes I believe to be the same as the sulcus
frontalis inferior in man. In this respect my views are in accordance with
those which were first expressed by Gratiolet. I see no reason for adopting
the opinion advanced by Eberstaller and Herv£, that in the human brain
it is the homologue of the sulcus frontalis medius.

Speaking of this furrow, Eberstaller says : " Die untere Stirnfurche des
Menschen ist er nicht, denn 1. ist die untere Stirnfurche des menschlichen
Hirns nicht gegen den Stirnpol ziehend, und 2. kann das Oberfla-
chengebiet, welches zwischen ihm und der Orbitalkante liegt, nicht als 3.
Stirnwindung gelten, denn diese schlagt sich, wie Bischoff ganz richtig
argumentirte, um die vordere Ecke der Sylvischen Grube herum. Was
aber dann ? "

I must confess that neither of these arguments appeal to me with any
force. The direction of the furrow in the brain of the low apes and in the
brain of man is undoubtedly different; but consider the difference of form
of the frontal lobe in the two cases. In the apes the frontal region is
narrow and pointed, and the superciliary margin is pushed high up wards
by the elevated convex orbital plate of the frontal bone. In man the
outer surface of the lobe has gained in breadth, and the superciliary
margin has descended. In what direction has the growth which has produced
the massive frontal lobe of man proceeded ? Certainly not in an
upward direction. Everything points to a general outward and downward
growth, and this affords us some explanation as to the change in the

* " Versuch einer Anatomie des Genus Hylobates." Zoologische Ergebnisse einer Eeise in
Niederlandiscb Ost-Indien. Band n., p. 188. Leiden, 1891.