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Djr. Cunningham—Surface Anatomy of the Primate Cerebrum. 71

question (PI. ii., fig. 17). A slight inequality on the surface of the cerebrum
which has been produced artificially might readily be mistaken for a
transitory furrow on the very verge of complete obliteration, and I am not
satisfied that the external calcarine furrow in this case was not produced
in this way. This is clearly a field for further investigation, because
until we have undoubted evidence of the two fissures being present on
the same hemisphere the question cannot be definitely settled.

Eberstaller* seems to doubt the transitory character of the external
perpendicular sulcus. He says:—"Wiirde die Affenspalte des Menschen
beim sechsmonatlichen Fotus vorhanden sein und im Laufe des achten
Monates verschwinden (Bischoff), so wiirde diese Thatsache in Hinsicht auf
die Ascendenz-Theorie eine weite Liicke zwischen dem Grenus Homo und den
Anthropoiden statuiren, denn je friiher die Daueraierkmale einer inferioren
Species in der- embryonalen Entwicklung der hoherstehenden Formen
auftreten und je hinfalliger sie sind, umso weiter ab voneinander liegen
beide Formen. Dass die Affenspalte nicht verschwindet, dass sie ein
bleibendes Artenmerkmal des Menschen ist, welches in der vollendeten
Entwicklungsform persistirt, dass sie iiberdies an weiblichen Gehirnen
gewohnlich einfacher ist wie an mannlichen, restituirt den Menschen als
unmittelbar an die Spitze der Anthropoiden gehorig und vermindert den
zeitlichen Abstand."

In this Eberstaller is clearly in error. In the vast majority of cases, as
we have seen, the fissura perpendicularis externa is undoubtedly obliterated.
As we shall see also later on, the fissure, which in the adult human brain is
generally regarded as the representative of the " Affenspalte," is really a
dependency of the intra-parietal sulcus.

XI. The Collateral Fissure.—The question which must next be
decided is one relating to the collateral fissure. Is this a complete fissure,
and if so, when and in what manner is it developed ? The collateral fissure-
is late of appearing. It is included by Pansch amongst the "Primar-
furche," and therefore classified by him with the fissure of Rolando, the

* Zur Oberflaclien-Anatornie der Grosshirnheniispharen. (Vorlaufige Mittheikmg.) ISTo. nr.,
Wiener Medizinisehe Blatter, 1884, Fo. 19.