On the Brain | Page 5

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.)
"So far as cerebral structure goes, therefore, it is clear that man differs
less from the chimpanzee or the orang, than these do even from the
monkeys, and that the difference between the brain of the chimpanzee
and of man is almost insignificant when compared with that between
the chimpanzee brain and that of a Lemur."
In the paper to which I have referred, Professor Bischoff does not deny
the second part of this statement, but he first makes the irrelevant
remark that it is not wonderful if the brains of an orang and a Lemur are
very different; and secondly, goes on to assert that, "If we successively
compare the brain of a man with that of an orang; the brain of this with
that of a chimpanzee; of this with that of a gorilla, and so on of a
Hylobates, Semnopithecus, Cynocephalus, Cercopithecus, Macacus,
Cebus, Callithrix, Lemur, Stenops, Hapale, we shall not meet with a

greater, or even as great a, break in the degree of development of the
convolutions, as we find between the brain of a man and that of an
orang or chimpanzee."
To which I reply, firstly, that whether this assertion be true or false, it
has nothing whatever to do with the proposition enunciated in 'Man's
Place in Nature,' which refers not to the development of the
convolutions alone, but to the structure of the whole brain. If Professor
Bischoff had taken the trouble to refer to p. 96 of the work he criticises,
in fact, he would have found the following passage: "And it is a
remarkable circumstance that though, so far as our present knowledge
extends, there IS one true structural break in the series of forms of
Simian brains, this hiatus does not lie between man and the manlike
apes, but between the lower and the lowest Simians, or in other words,
between the Old and New World apes and monkeys and the Lemurs.
Every Lemur which has yet been examined, in fact, has its cerebellum
partially visible from above; and its posterior lobe, with the contained
posterior cornu and hippocampus minor, more or less rudimentary.
Every marmoset, American monkey, Old World monkey, baboon or
manlike ape, on the contrary, has its cerebellum entirely hidden,
posteriorly, by the cerebral lobes, and possesses a large posterior cornu
with a well-developed hippocampus minor."
This statement was a strictly accurate account of what was known when
it was made; and it does not appear to me to be more than apparently
weakened by the subsequent discovery of the relatively small
development of the posterior lobes in the Siamang and in the Howling
monkey. Notwithstanding the exceptional brevity of the posterior lobes
in these two species, no one will pretend that their brains, in the
slightest degree, approach those of the Lemurs. And if, instead of
putting Hapale out of its natural place, as Professor Bischoff most
unaccountably does, we write the series of animals he has chosen to
mention as follows: Homo, Pithecus, Troglodytes, Hylobates,
Semnopithecus, Cynocephalus, Cercopithecus, Macacus, Cebus,
Callithrix, Hapale, Lemur, Stenops, I venture to reaffirm that the great
break