terminating his fore limbs, and of two feet ending his hind limbs, while
it has been said that all the apes possess four hands; and he has been
affirmed to differ fundamentally from all the apes in the characters of
his brain, which alone, it has been strangely asserted and re-asserted,
exhibits the structures known to anatomists as the posterior lobe, the
posterior cornu of the lateral ventricle, and the hippocampus minor.
That the former proposition should have gained general acceptance is not
surprising--indeed, at first sight, appearances are much in its favour:
but, as for the second, one can only admire the surpassing courage
of its enunciator, seeing that it is an innovation which is not only
opposed to generally and justly accepted doctrines, but which is
directly negatived by the testimony of all original inquirers, who have
specially investigated the matter: and that it neither has been, nor can
be, supported by a single anatomical preparation. It would, in fact,
be unworthy of serious refutation, except for the general and natural
belief that deliberate and reiterated assertions must have some
foundation.
Before we can discuss the first point with advantage we must consider
with some attention, and compare together, the structure of the human
hand and that of the human foot, so that we may have distinct and clear
ideas of what constitutes a hand and what a foot.
The external form of the human hand is familiar enough to every one. It
consists of a stout wrist followed by a broad palm, formed of flesh, and
tendons, and skin, binding together four bones, and dividing into four
long and flexible digits, or fingers, each of which bears on the back of
its last joint a broad and flattened nail. The longest cleft between any
two digits is rather less than half as long as the hand. From the outer
side of the base of the palm a stout digit goes off, having only two
joints instead of three; so short, that it only reaches to a little
beyond the middle of the first joint of the finger next it; and further
remarkable by its great mobility, in consequence of which it can be
directed outwards, almost at a right angle to the rest. This digit is
called the 'pollex,' or thumb; and, like the others, it bears a
flat nail upon the back of its terminal joint. In consequence of the
proportions and mobility of the thumb, it is what is termed "opposable";
in other words, its extremity can, with the greatest ease, be brought
into contact with the extremities of any of the fingers; a property upon
which the possibility of our carrying into effect the conceptions of the
mind so largely depends.
The external form of the foot differs widely from that of the hand; and
yet, when closely compared, the two present some singular resemblances.
Thus the ankle corresponds in a manner with the wrist; the sole with the
palm; the toes with the fingers; the great toe with the thumb. But the
toes, or digits of the foot, are far shorter in proportion than the
digits of the hand, and are less moveable, the want of mobility being
most striking in the great toe--which, again, is very much larger
in proportion to the other toes than the thumb to the fingers. In
considering this point, however, it must not be forgotten that the
civilized great toe, confined and cramped from childhood upwards, is
seen to a great disadvantage, and that in uncivilized and barefooted
people it retains a great amount of mobility, and even some sort of
opposability. The Chinese boatmen are said to be able to pull an oar;
the artisans of Bengal to weave, and the Carajas to steal fishhooks, by
its help; though, after all, it must be recollected that the structure
of its joints and the arrangement of its bones, necessarily render its
prehensile action far less perfect than that of the thumb.
But to gain a precise conception of the resemblances and differences of
the hand and foot, and of the distinctive characters of each, we must
look below the skin, and compare the bony framework and its motor
apparatus in each (Fig. 18).
[Illustration: FIG. 18--The skeleton of the Hand and Foot of Man reduced
from Dr. Carter's drawings in Gray's 'Anatomy.' The hand is drawn to
a larger scale than the foot. The line 'a a' in the hand indicates the
boundary between the carpus and the metacarpus; 'b b' that between the
latter and the proximal phalanges; 'c c' marks the ends of the distal
phalanges. The line "a' a'" in the foot indicates the boundary between
the tarsus and metatarsus; "b' b'" marks that between the metatarsus
and the proximal phalanges; and "c' c'" bounds the ends of the distal
phalanges; 'ca', the calcaneum; 'as', the astragalus; 'sc', the scaphoid
bone in the tarsus.]
The skeleton of the hand exhibits, in the region which we term the
wrist, and which is technically called the 'carpus'--two rows of closely
fitted polygonal bones, four in each row, which are tolerably equal in
size. The bones of the first row with the bones of the forearm, form the
wrist joint, and are arranged side by side, no one greatly exceeding or
overlapping the rest.
The four bones of the second row of the carpus bear the four long bones
which support the palm of the hand. The fifth bone of the same character
is articulated in a much more free and moveable manner than the others,
with its carpal bone, and forms the base of the thumb. These are called
'metacarpal' bones, and they carry the 'phalanges', or bones of the
digits, of which there are two in the thumb, and three in each of the
fingers.
The skeleton of the foot is very like that of the hand in some respects.
Thus there are three phalanges in each of the lesser toes, and only
two in the great toe, which answers to the thumb. There is a long bone,
termed 'metatarsal', answering to the metacarpal, for each digit; and
the 'tarsus', which corresponds with the carpus, presents four short
polygonal bones in a row, which correspond very closely with the four
carpal bones of the second row of the hand. In other respects the foot
differs very widely from the hand. Thus the great toe is the longest
digit but one; and its metatarsal is far less moveably articulated with
the tarsus, than the metacarpal of the thumb with the carpus. But a far
more important distinction lies in the fact that, instead of four
more tarsal bones there are only three; and, that these three are not
arranged side by side, or in one row. One of them, the 'os calcis' or
heel bone ('ca'), lies externally, and sends back the large projecting
heel; another, the 'astragalus' ('as'), rests on this by one face, and
by another, forms, with the bones of the leg, the ankle joint; while a
third face, directed forwards, is separated from the three inner tarsal
bones of the row next the metatarsus by a bone called the 'scaphoid'
('sc').
Thus there is a fundamental difference in the structure of the foot and
the hand, observable when the carpus and the tarsus are contrasted; and
there are differences of degree noticeable when the proportions and
the mobility of the metacarpals and metatarsals, with their respective
digits, are compared together.
The same two classes of differences become obvious when the muscles of
the hand are compared with those of the foot.
Three principal sets of muscles, called "flexors," bend the fingers and
thumb, as in clenching the fist, and three sets--the extensors--extend
them, as in straightening the fingers. These muscles are all "long
muscles"; that is to say, the fleshy part of each, lying in and being
fixed to the bones of the arm, is, at the other end, continued into
tendons, or rounded cords, which pass into the hand, and are ultimately
fixed to the bones which are to be moved. Thus, when the fingers are
bent, the fleshy parts of the flexors of the fingers, placed in the arm,
contract, in virtue of their peculiar endowment as muscles; and pulling
the tendinous cords, connected with their ends, cause them to pull down
the bones of the fingers towards the palm.
Not only are the principal flexors of the fingers and of the thumb long
muscles, but they remain quite distinct from one another through their
whole length.
In the foot, there are also three principal flexor muscles of the digits
or toes, and three principal extensors; but one extensor and one flexor
are short muscles; that is to say, their fleshy parts are not situated
in the leg (which corresponds with the arm), but in the back and in the
sole of the foot--regions which correspond with the back and the palm of
the hand.
Again, the tendons of the long flexor of the toes, and of the long
flexor of the great toe, when they reach the sole of the foot, do not
remain distinct from one another, as the flexors in the palm of the
hand do, but they become united and commingled in a very curious
manner--while their united tendons receive an accessory muscle connected
with the heel-bone.
But perhaps the most absolutely distinctive character about the muscles
of the foot is the existence of what is termed the 'peronaeus longus',
a long muscle fixed to the outer bone of the leg, and sending its tendon
to the outer ankle, behind and below which it passes, and then crosses
the foot obliquely to be attached to the base of the great toe. No
muscle in the hand exactly corresponds with this, which is eminently a
foot muscle.
To resume--the foot of man is distinguished from his hand by the
following absolute anatomical differences:--
1. By the arrangement of the tarsal bones.
2. By having a short flexor and a short extensor muscle of the digits.
3. By possessing the muscle termed 'peronaeus longus'.
And if we desire to ascertain whether the terminal division of a limb,
in other Primates, is to be called a foot or a hand, it is by the
presence or absence of these characters that we must be guided, and not
by the mere proportions and greater or lesser mobility of the great toe,
which may vary indefinitely without any fundamental alteration in the
structure of the foot.
Keeping these considerations in mind, let us now turn to the limbs
of the Gorilla. The terminal division of the fore limb presents no
difficulty--bone for bone and muscle for muscle, are found to be
arranged essentially as in man, or with such minor differences as are
found as varieties in man. The Gorilla's hand is clumsier, heavier, and
has a thumb somewhat shorter in proportion than that of man; but no one
has ever doubted its being a true hand.
[Illustration: FIG 19.--Foot of Man, Gorilla, and Orang-Utan of the same
absolute length, to show the differences in proportion of each.
Letters as in Fig. 18. Reduced from original drawings by Mr. Waterhouse
Hawkins.]
At first sight, the termination of the hind limb of the Gorilla looks
very hand-like, and as it is still more so in many of the lower apes,
it is not wonderful that the appellation "Quadrumana," or four-handed
creatures, adopted from the older anatomists [5] by Blumenbach, and
unfortunately rendered current by Cuvier, should have gained such
wide acceptance as a name for the Simian group. But the most cursory
anatomical investigation at once proves that the resemblance of the
so-called "hind hand" to a true hand, is only skin deep, and that,
in all essential respects, the hind limb of the Gorilla is as truly
terminated by a foot as that of man. The tarsal bones, in all important
circumstances of number, disposition, and form, resemble those of
man (Fig. 19). The metatarsals and digits, on the other hand, are
proportionally longer and more slender, while the great toe is not only
proportionally shorter and weaker, but its metatarsal bone is united by
a more moveable joint with the tarsus. At the same time, the foot is set
more obliquely upon the leg than in man.
As this passage was published in 1699, M. I. G. St. Hilaire is clearly
in error in ascribing the invention of the term "quadrumanous" to
Buffon, though "himanous" may belong to him. Tyson uses "Quadrumanus"
in several places, as at p. 91.... "Our 'Pygmie' is no Man, nor yet the
'common Ape', but a sort of 'Animal' between both; and though a 'Biped',
yet of the 'Quadrumanus'-kind: though some 'Men' too have been observed
to use their 'Feet' like 'Hands', as I have seen several."
As to the muscles, there is a short flexor, a short extensor, and a
'peronaeus longus', while the tendons of the long flexors of the great
toe and of the other toes are united together and with an accessory
fleshy bundle.
The hind limb of the Gorilla, therefore, ends in a true foot, with a
very moveable great toe. It is a prehensile foot, indeed, but is in no
sense a hand: it is a foot which differs from that of man not in
any fundamental character, but in mere proportions, in the degree of
mobility, and in the secondary arrangement of its parts.
It must not be supposed, however, because I speak of these differences
as not fundamental, that I wish to underrate their value. They are
important enough in their way, the structure of the foot being in strict
correlation with that of the rest of the organism in each case. Nor can
it be doubted that the greater division of physiological labour in Man,
so that the function of support is thrown wholly on the leg and foot, is
an advance in organization of very great moment to him; but, after all,
regarded anatomically, the resemblances between the foot of Man and
the foot of the Gorilla are far more striking and important than the
differences.
I have dwelt upon this point at length, because it is one regarding
which much delusion prevails; but I might have passed it over without
detriment to my argument, which only requires me to show that, be the
differences between the hand and foot of Man and those of the Gorilla
what they may--the differences between those of the Gorilla, and those
of the lower Apes are much greater.
It is not necessary to descend lower in the scale than the Orang for
conclusive evidence on this head.
The thumb of the Orang differs more from that of the Gorilla than
the thumb of the Gorilla differs from that of Man, not only by its
shortness, but by the absence of any special long flexor muscle. The
carpus of the Orang, like that of most lower apes, contains nine bones,
while in the Gorilla, as in Man and the Chimpanzee, there are only
eight.
The Orang's foot (Fig. 19) is still more aberrant; its very long
toes and short tarsus, short great toe, short and raised heel, great
obliquity of articulation in the leg, and absence of a long flexor
tendon to the great toe, separating it far more widely from the foot of
the Gorilla than the latter is separated from that of Man.
But, in some of the lower apes, the hand and foot diverge still more
from those of the Gorilla, than they do in the Orang. The thumb ceases
to be opposable in the American monkeys; is reduced to a mere rudiment
covered by the skin in the Spider Monkey; and is directed forwards and
armed with a curved claw like the other digits, in the Marmosets--so
that, in all these cases, there can be no doubt but that the hand is
more different from that of the Gorilla than the Gorilla's hand is from
Man's.
And as to the foot, the great toe of the Marmoset is still more
insignificant in proportion than that of the Orang--while in the Lemurs
it is very large, and as completely thumb-like and opposable as in
the Gorilla--but in these animals the second toe is often irregularly
modified, and in some species the two principal bones of the tarsus,
the 'astragalus' and the 'os calcis', are so immensely elongated as to
render the foot, so far, totally unlike that of any other mammal.
So with regard to the muscles. The short flexor of the toes of the
Gorilla differs from that of Man by the circumstance that one slip of
the muscle is attached, not to the heel bone, but to the tendons of the
long flexors. The lower Apes depart from the Gorilla by an exaggeration
of the same character, two, three, or more, slips becoming fixed to the
long flexor tendons--or by a multiplication of the slips.--Again, the
Gorilla differs slightly from Man in the mode of interlacing of the long
flexor tendons: and the lower apes differ from the Gorilla in exhibiting
yet other, sometimes very complex, arrangements of the same parts, and
occasionally in the absence of the accessory fleshy bundle.
Throughout all these modifications it must be recollected that the
foot loses no one of its essential characters. Every Monkey and Lemur
exhibits the characteristic arrangement of tarsal bones, possesses a
short flexor and short extensor muscle, and a 'peronaeus longus'. Varied
as the proportions and appearance of the organ may be, the terminal
division of the hind limb remains, in plan and principle of
construction, a foot, and never, in those respects, can be confounded
with a hand.
Hardly any part of the bodily frame, then, could be found better
calculated to illustrate the truth that the structural differences
between Man and the highest Ape are of less value than those between the
highest and the lower Apes, than the hand or the foot, and yet, perhaps,
there is one organ the study of which enforces the same conclusion in a
still more striking manner--and that is the Brain.
But before entering upon the precise question of the amount of
difference between the Ape's brain and that of Man, it is necessary that
we should clearly understand what constitutes a great, and what a small
difference in cerebral structure; and we shall be best enabled to
do this by a brief study of the chief modifications which the brain
exhibits in the series of vertebrate animals.
The brain of a fish is very small, compared with the spinal cord into
which it is continued, and with the nerves which come off from it: of
the segments of which it is composed--the olfactory lobes, the cerebral
hemisphere, and the succeeding divisions--no one predominates so much
over the rest as to obscure or cover them; and the so-called optic lobes
are, frequently, the largest masses of all. In Reptiles, the mass of
the brain, relatively to the spinal cord, increases and the cerebral
hemispheres begin to predominate over the other parts; while in Birds
this predominance is still more marked. The brain of the lowest Mammals,
such as the duck-billed Platypus and the Opossums and Kangaroos,
exhibits a still more definite advance in the same direction. The
cerebral hemispheres have now so much increased in size as, more or
less, to hide the representatives of the optic lobes, which remain
comparatively small, so that the brain of a Marsupial is extremely
different from that of a Bird, Reptile, or Fish. A step higher in the
scale, among the placental Mammals, the structure of the brain acquires
a vast modification--not that it appears much altered externally, in
a Rat or in a Rabbit, from what it is in a Marsupial--nor that the
proportions of its parts are much changed, but an apparently new
structure is found between the cerebral hemispheres, connecting them
together, as what is called the 'great commissure' or 'corpus callosum.'
The subject requires careful re-investigation, but if the currently
received statements are correct, the appearance of the 'corpus callosum'
in the placental mammals is the greatest and most sudden modification
exhibited by the brain in the whole series of vertebrated animals--it is
the greatest leap anywhere made by Nature in her brain work. For the
two halves of the brain being once thus knit together, the progress of
cerebral complexity is traceable through a complete series of steps from
the lowest Rodent, or Insectivore, to Man; and that complexity consists,
chiefly, in the disproportionate development of the cerebral hemispheres
and of the cerebellum, but especially of the former, in respect to the
other parts of the brain.
In the lower placental mammals, the cerebral hemispheres leave the
proper upper and posterior face of the cerebellum completely visible,
when the brain is viewed from above; but, in the higher forms, the
hinder part of each hemisphere, separated only by the tentorium (p.
281) from the anterior face of the cerebellum, inclines backwards and
downwards, and grows out, as the so-called "posterior lobe," so as at
length to overlap and hide the cerebellum. In all Mammals, each cerebral
hemisphere contains a cavity which is termed the 'ventricle,' and as
this ventricle is prolonged, on the one hand, forwards, and on the other
downwards, into the substance of the hemisphere, it is said to have two
horns or 'cornua, an 'anterior cornu,' and a 'descending cornu.' When
the posterior lobe is well developed, a third prolongation of the
ventricular cavity extends into it, and is called the "posterior cornu."
In the lower and smaller forms of placental Mammals the surface of the
cerebral hemispheres is either smooth or evenly rounded, or exhibits a
very few grooves, which are technically termed 'sulci,'separating ridges
or 'convolutions' of the substance of the brain; and the smaller species
of all orders tend to a similar smoothness of brain. But, in the higher
orders, and especially the larger members of these orders, the grooves,
or sulci, become extremely numerous, and the intermediate convolutions
proportionately more complicated in their meanderings, until, in the
Elephant, the Porpoise, the higher Apes, and Man, the cerebral surface
appears a perfect labyrinth of tortuous foldings.
Where a posterior lobe exists and presents its customary cavity--the
posterior cornu--it commonly happens that a particular sulcus appears
upon the inner and under surface of the lobe, parallel with and beneath
the floor of the cornu--which is, as it were, arched over the roof of
the sulcus. It is as if the groove had been formed by indenting the
floor of the posterior horn from without with a blunt instrument, so
that the floor should rise as a convex eminence. Now this eminence is
what has been termed the 'Hippocampus minor;' the 'Hippocampus major'
being a larger eminence in the floor of the descending cornu. What may
be the functional importance of either of these structures we know not.
As if to demonstrate, by a striking example, the impossibility of
erecting any cerebral barrier between man and the apes, Nature has
provided us, in the latter animals, with an almost complete series of
gradations from brains little higher than that of a Rodent, to brains
little lower than that of Man. 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 man-like 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 Man-like 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.
[Illustration: FIG. 20.--Drawings of the internal casts of a Man's and
of a Chimpanzee's skull, of the same absolute length, and placed in
corresponding positions. 'A'. Cerebrum; 'B'. Cerebellum. The former
drawing is taken from a cast in the Museum of the Royal College of
Surgeons, the latter from the photograph of the cast of a Chimpanzee's
skull, which illustrates the paper by Mr. Marshall 'On the Brain of the
Chimpanzee' in the 'Natural History Review' for July, 1861. The sharper
definition of the lower edge of the cast of the cerebral chamber in the
Chimpanzee arises from the circumstance that the tentorium remained in
that skull and not in the Man's. The cast more accurately represents the
brain in Chimpanzee than in the Man; and the great backward projection
of the posterior lobes of the cerebrum of the former, beyond the
cerebellum, is conspicuous.]