There remains, then, no dispute as to the resemblance in
fundamental characters, between the ape's brain and man's: nor
any as to the wonderfully close similarity between the
chimpanzee, orang and man, in even the details of the arrangement
of the gyri and sulci of the cerebral hemispheres. Nor, turning
to the differences between the brains of the highest apes and
that of man, is there any serious question as to the nature and
extent of these differences. It is admitted that the man's
cerebral hemispheres are absolutely and relatively larger than
those of the orang and chimpanzee; that his frontal lobes are
less excavated by the upward protrusion of the roof of the
orbits; that his gyri and sulci are, as a rule, less
symmetrically disposed, and present a greater number of secondary
plications. And it is admitted that, as a rule, in man, the
temporo-occipital or "external perpendicular" fissure, which is
usually so strongly marked a feature of the ape's brain is but
faintly marked. But it is also clear, that none of these
differences constitutes a sharp demarcation between the man's and
the ape's brain. In respect to the external perpendicular
fissure of Gratiolet, in the human brain for instance, Professor
Turner remarks: (71. 'Convolutions of the Human Cerebrum
Topographically Considered,' 1866, p. 12.)

"In some brains it appears simply as an indentation of the margin
of the hemisphere, but, in others, it extends for some distance
more or less transversely outwards. I saw it in the right
hemisphere of a female brain pass more than two inches outwards;
and on another specimen, also the right hemisphere, it proceeded
for four-tenths of an inch outwards, and then extended downwards,