descriptions, is also well illustrated in these specimens (pp. 8, 9).
Even were the presence of the temporo-occipital, or external
perpendicular, sulcus, a mark of distinction between the higher apes
and man, the value of such a distinctive character would be rendered
very doubtful by the structure of the brain in the Platyrrhine apes. In
fact, while the temporo-occipital is one of the most constant of sulci
in the Catarrhine, or Old World, apes, it is never very strongly
developed in the New World apes; it is absent in the smaller
Platyrrhini; rudimentary in Pithecia (73. Flower, On the Anatomy of
Pithecia Monachus, Proceedings of the Zoological Society, 1862.);
and more or less obliterated by bridging convolutions in Ateles.
A character which is thus variable within the limits of a single group
can have no great taxonomic value.
It is further established, that the degree of asymmetry of the
convolution of the two sides in the human brain is subject to much
individual variation; and that, in those individuals of the Bushman
race who have been examined, the gyri and sulci of the two hemispheres
are considerably less complicated and more symmetrical than in the
European brain, while, in some individuals of the chimpanzee, their
complexity and asymmetry become notable. This is particularly the case
in the brain of a young male chimpanzee figured by M. Broca. ( L ordre
des Primates, p. 165, fig. 11.)
Again, as respects the question of absolute size, it is established
that the difference between the largest and the smallest healthy human
brain is greater than the difference between the smallest healthy human
brain and the largest chimpanzee s or orang s brain.
Moreover, there is one circumstance in which the orang s and
chimpanzee s brains resemble man s, but in which they differ from the
lower apes, and that is the presence of two corpora candicantia the
Cynomorpha having but one.
In view of these facts I do not hesitate in this year 1874, to repeat
and insist upon the proposition which I enunciated in 1863: (74. Man s
Place in Nature, p. 102.)
223