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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 209

die zuerst auftretenden werden stets tief. Man kann also am ausgewach-
senen Hirn die Entwicklungsgeschichte der Furchen (Faltungen) einiger-
maassen ablesen, in dem man die Tiefe der Furchen untersucht." *

If we accept this proposition the relative morphological value attached
to the fissure of Rolando and the intraparietal sulcus is different in man
and in the ape, inasmuch as we must assume that the lower we descend
in the primates the less becomes the importance attached to the fissure
of Rolando, and the greater the value of the intraparietal sulcus. For
my own part I am inclined to believe that this is really the case, but it
is a question upon which it is difficult to offer a decided opinion, seeing
that we are altogether ignorant as to the order in which these two furrows
develope in the apes. The study of the phylogenetic evolution of the
two furrows under consideration certainly points to the intraparietal
sulcus as possessing a preponderating importance; and in connexion with
this a paragraph in the address which was delivered in Berlin by Sir
William Turner f presents the highest interest. Speaking of the fissure
of Rolando he says :—" In the Prosimian Stenops and in Lemur nigrifrons
it is absent. No vestige of it can be seen in the Platyrrhine marmoset;
but it is distinct in the Platyrrhine genera Pithecia, Ateles, Cebus, &c. . . .
It is true that the marmoset has a perfectly smooth cerebrum above and in
front of the Sylvian fissure; but the hemisphere of Stenops possesses in its
more anterior part rudimentary fissures extending antero-posteriorly, which
mark the commencement of a differentiation into tiers of convolutions
extending in a sagittal direction, such as one is familiar with in the frontal
lobe of the higher apes. Corresponding anteroposterior fissures exist also
in Lemur nigrifrons, and another fissure is placed further backwards, which
is probably the homologue of the intraparietal fissure in the higher brains."
The evidence thus afforded is decidedly in favour of regarding the intraparietal
sulcus as possessing a greater phylogenetic antiquity than the
fissure of Rolando.

Pansch was well aware of the greater depth of the intraparietal sulcus

* "Einige Satze iiber die Grosshirnfaltungen,'' Centralblatt fur die niedizinischen Wissen-
schaften, No. 36, 1877, p. 643.

f J oiirnal of Anatomy and Physiology, vol. xxv., p. 2.

ROYAL IRISH ACADEMY.-CUNNINGHAM MEMOIRS, NO. VH. [271

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