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66

Cunningham Memoirs.

an unsatisfactory plan, and the results obtained in this way cannot be
accepted as being in every case absolutely accurate.

It will be seen, therefore, that the cranio-cerebral relations in the
anthropoid apes, in so far as this fissure is concerned, are somewhat similar,
to those in man. Very different, however, are the corresponding relations
in the lower apes. In all of these, with their large occipital lobes, the
fissure, as is seen from the indices, lies well in front of the lambda. Very
considerable differences in this respect are exhibited in different varieties
of apes. In the baboon and hamadryas it will be seen that the relative
distance between the two points in question is not so great as in the
macaque and the cebus. Fe>e\ in the Paper above referred to, gives us a
great deal of information on the cranio-cerebral topography of the apes.
He examined a large number of different varieties of apes, and in some cases
as many as twelve specimens of one species. Unfortunately he only gives
the absolute measurements, and these are, therefore of little value in the
present research, where we are dealing entirely with relative results.

X. External Perpendicular and External Calcarine Fissures.—In

his elaborate Memoir upon the convolutions of the human brain and their
development in the foetus, Bischoff * describes and figures a transitory
fissure on the outer surface of the cerebral hemisphere under the name of
" fissura perpendicularis externa." He states that it appears towards the
end of the seventh month on the outer surface of the hemisphere, near its
hinder end, in the form of a furrow, which runs downwards in a
vertical direction. And then, further on (p. 449), he adds:—"But the
fissure, which we have designated above the fissura perpendicularis
externa, does not develop any further, . . . but disappears again in the
course of the eighth month without taking any part in the formation
of the later furrows on the occipital region." It belongs, therefore,
he remarks, to that class of formations which only in certain forms (in
the apes) attain their complete development, whilst in others they are
arrested or completely disappear.

That such a fissure as a general rule exists on the foetal human brain

* Abbandl. der k. bayer Akacl. der Wiss., 11 CI. x. Bd. 11 Abth., p. 448.