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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 185

gradual developmental predominance which the frontal lobe gains in
comparison with the parietooccipital portion of the cerebrum during the
increase of the human brain and that of the primates, the same law of
evolution is exactly reproduced which has regulated the development of the
superficies of the mantle in the phylogenesis of the primates. Inasmuch as
the greater development of the frontal brain, in comparison with the
parietooccipital, distinguishes the brain of man from that of the other
primates, of the adult from that of the foetus, of the male from that of the
female, of the intelligent from that of idiots, it is reasonable to suppose
that this fact ought to be established as one of the fundamental characteristics
of the psychic evolution in the primates and in man." In so far as we can
judge the size of the frontal lobe by tape measurement, it is not relatively
greater in the adult than in the foetus, nor in the male than in the female;
and further, although the frontal lobe is extremely small in all apes,
still in the anthropoid apes it is, in its upper part, relatively longer than
in man. It appears to me that the parietal and occipital lobes throughout
the order Primates are equally distinctive.

In the foregoing Table the relations presented by the fissure of Rolando
to the cranial wall are also expressed by a series of corono-Eolandic indices.
In the chimpanzee the upper corono-Rolandic index (16) is very nearly in
accord with the corresponding index in man (16#7). The position of the
upper end of the fissure, therefore, with reference to the bregma, is relatively
the same in both. In the orang the distance between the suture and
the upper end of the sulcus is relatively much greater, as evidenced by the
index of 20-7. In the chimpanzee the lower end of the fissure approaches
much more closely to the coronal suture (index 7*5) than in man (index
12*9), or in the orang (index 11*1). The position of the fissure of Rolando,
with reference to the coronal suture in the chimpanzee and orang, is exhibited
in Plate vni.

As might be expected, we find that in the lower apes of the old world
the fissure of Rolando throughout its whole length lies nearer to the coronal
suture than in man. In Plate vni. these relations are exhibited in the
macaque and baboon.

In Cebus the relations of the fissure of Rolando to the cranial wall

BOYAL IRISH ACADEMY.-CUNNINGHAM MEMOIRS, NO. VII. [241