Part 2 (1/2)

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).

[Ill.u.s.tration: 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 cla.s.ses of differences become obvious when the muscles of the hand are compared with those of the foot.

Three princ.i.p.al 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 pa.s.s 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 princ.i.p.al 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 princ.i.p.al flexor muscles of the digits or toes, and three princ.i.p.al 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 pa.s.ses, 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.

[Ill.u.s.tration: 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 circ.u.mstances 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 pa.s.sage 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 ”Quadruma.n.u.s”

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 'Quadruma.n.u.s'-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.