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De. Cunningham—Surface Anatomy of the Primate Cerebrum. 173

Eberstaller. In the anthropoid ape the connexion of this element with the
main furrow appears to be more intimate than in man. Of course, in man
it cannot be placed on the same footing as the other two elements, seeing
that it appears so much later (eighth month),* and that it may establish
other connexions besides that with the Rolandic sulcus.

As I shall point out further on, the fissure of Rolando is very much
longer in the anthropoid apes than in man. If we represent the length of
the fissure of Rolando in the human brain by the number 100, we find that
in the chimpanzee it is 130, and in the orang 120. It appears to me,
therefore, not improbable that this lower element, so variable and inconstant
in its present connexions, may have had at one time a closer association
with the fissure of Rolando in man. In all the anthropoid hemispheres in
my possession, with one exception, the lower portion of the fissure of Rolando
is partially cut off by a deep annectant gyrus.

It is not uncommon to find the lower portion of the prsecentral fissure
developed in the earlier part of the fifth month, prior to the appearance of
the fissure of Rolando. I have six hemispheres which show this condition,
and under these circumstances the prsecentral sulcus is very apt to be
mistaken for the fissure of Rolando. Its position in front of the middle of
the hemisphere and in front of the coronal suture should, in all cases,
enable us to detect its true nature (PI. i., figs. 14 and 17 ; also PI. n., figs.
8 and 9, p. c). At the same time, I may mention that it was not until I had
obtained two hemispheres belonging to this early period, in which the
fissure in question was strongly marked, and in which also there was a
slight trace of the fissure of Rolando, that I was thoroughly satisfied as to
its identity. I have only seen one hemisphere in which the third radial
" Primarfurche " or intraparietal sulcus was developed before the Rolandic
sulcus.

The inferior genu of the fissure of Rolando always makes its appearance
before the superior genu. As Eberstaller has stated it is usually well-
marked about the seventh month of intrauterine development. This is

* In one hemisphere, between the seventh and eighth months, I have seen it making its
appearance (PI. 11., fig. 24) ; but, as a rule, it does not come into existence until the eighth
month.