On the Brain(大脑)

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On the brain

PROFESSOR T.H. HUXLEY, F.R.S.

On the brain

[This essay is taken from 'The Descent of Man and Selection in

relation to Sex' by Charles Darwin where it appears at the end of

Chapter VII which is also the end of Part I. Footnotes are numbered

as they appear in 'The Descent of Man.']

The controversy respecting the nature and the extent of the

differences in the structure of the brain in man and the apes, which arose

some fifteen years ago, has not yet come to an end, though the subject

matter of the dispute is, at present, totally different from what it was

formerly. It was originally asserted and re-asserted, with singular

pertinacity, that the brain of all the apes, even the highest, differs from that

of man, in the absence of such conspicuous structures as the posterior

lobes of the cerebral hemispheres, with the posterior cornu of the lateral

ventricle and the hippocampus minor, contained in those lobes, which are

so obvious in man.

But the truth that the three structures in question are as well developed

in apes' as in human brains, or even better; and that it is characteristic of

all the Primates (if we exclude the Lemurs) to have these parts well

developed, stands at present on as secure a basis as any proposition in

comparative anatomy. Moreover, it is admitted by every one of the long

series of anatomists who, of late years, have paid special attention to the

arrangement of the complicated sulci and gyri which appear upon the

surface of the cerebral hemispheres in man and the higher apes, that they

are disposed after the very same pattern in him, as in them. Every

principal gyrus and sulcus of a chimpanzee's brain is clearly represented in

that of a man, so that the terminology which applies to the one answers for

the other. On this point there is no difference of opinion. Some years

since, Professor Bischoff published a memoir (70. 'Die Grosshirn-

Windungen des Menschen;' 'Abhandlungen der K. Bayerischen

Akademie,' B. x. 1868.) on the cerebral convolutions of man and apes; and

as the purpose of my learned colleague was certainly not to diminish the

value of the differences between apes and men in this respect, I am glad to

make a citation from him.

"That the apes, and especially the orang, chimpanzee and gorilla, come

On the brain

very close to man in their organisation, much nearer than to any other

animal, is a well known fact, disputed by nobody. Looking at the matter

from the point of view of organisation alone, no one probably would ever

have disputed the view of Linnaeus, that man should be placed, merely as

a peculiar species, at the head of the mammalia and of those apes. Both

shew, in all their organs, so close an affinity, that the most exact

anatomical investigation is needed in order to demonstrate those

differences which really exist. So it is with the brains. The brains of man,

the orang, the chimpanzee, the gorilla, in spite of all the important

differences which they present, come very close to one another" (loc. cit. p.

101).

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-

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Onthebrain1OnthebrainBYPROFESSORT.H.HUXLEY,F.R.S.Onthebrain2[Thisessayistakenfrom'TheDescentofManandSelectioninrelationtoSex'byCharlesDarwinwhereitappearsattheendofChapterVIIwhichisalsotheendofPartI.Footnotesarenumberedastheyappearin'TheDescentofMan.']Thecontroversyrespectingthenatureandtheextentoft...

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On the Brain(大脑)

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