Part 3
_One_ of the three joints--strictly called the “ankle-joint”--is between the leg-bones and the foot-bones, that is, between the tibia and fibula, above, and the astragalus beneath. By means of it the foot may be bent or straightened upon the leg; in other words, the toes may be raised or depressed. In this movement the heel participates, being depressed when the toes are raised, and _vice versâ_. A _second_ joint is between the astragalus and the heel-bone. It permits the foot to be rolled inwards or outwards upon an antero-posterior axis; so that the sole may be turned inwards, with its inner edge upwards, or may be turned down so as to be placed flat upon the ground. A _third_ joint is between the first and second row of tarsal bones--that is, between the astragalus and the heel bone, behind, and the scaphoid and cuboid bones in front. It permits the degree of flexure of the tarsal or plantar arch to be increased or diminished.
Had the several movements which are requisite for easy walking all taken place in one joint, that joint must necessarily have been very insecure; indeed, it must have been a “ball-and-socket” joint, and we should have been poised upon our feet in the state of what is called “unstable equilibrium”--a state quite incompatible with security or strength, and which would have rendered the assistance of the upper limbs essential to either standing or walking.
An instance of a similar kind of mechanism to this of the joints between the foot and the leg is presented by the mode in which the head is secured upon the back-bone. We can nod the head upwards and downwards; we can turn it to either side in so free a manner that we are able to command with our eyes the whole circle in which we sit simply by the movements of the head; and we can incline the head to the right or to the left. Any of these movements may be made very quickly; and there is a separate joint or joints for each of them. Thus, the _nodding_ movement takes place between the head and the first vertebra or uppermost bone of the spine; the _turning_ of the head from side to side takes place between the first and second vertebræ, the head with the first vertebra rotating upon a pivot projected upwards from the second vertebra; and the _inclination_ of the head from side to side takes place by movements of the second vertebra upon the third, of the third upon the fourth, and so on. The result is that, although the movements are thus varied, they are free as well as rapid. Yet the head is so well poised and so strongly fixed that the neck is able to bear it all day long without fatigue; and, as though the weight of the head, which is by no means inconsiderable, were not enough for the neck, we are in the habit of selecting this as the part upon which to carry burdens. One never feels so strongly impressed with the carrying capabilities of the neck and the ankle, as when following men and women in mountain districts toiling up and down the hills under great bundles of hay, baskets full of bitter beer, and various things intended to minister to the comfort and luxury of travellers and the inhabitants at the top. So effectual, indeed, are the provisions for security that, notwithstanding the freedom and variety of their movements, the joints of the foot with the leg, and of the head with the spine, are, in proportion to their size, the strongest in the body.
I have stated the movements that take place in the three joints of the foot with the leg in a simple manner, for the sake of avoiding confusion. In reality, however, they are not so simple, but very difficult to analyse and make out correctly. The difficulty is due, partly, to the close proximity of the joints to one another, which renders it no easy matter to distinguish the movements of one from those of the others, and, partly, to the fact that the movements in each joint are a little oblique.
In the latter respect the foot-joints resemble most of the others in the body; and it is this _obliquity_ in the movements of the joints, added to the _curves_ and _twists_ in the shape of the bones, that constitutes one of the chief difficulties in investigating and clearly understanding the mechanism of the human frame. It has been said that “Nature abhors a vacuum:” it may with equal truth be said that she abhors a straight line. In the Human Skeleton, at any rate, all the bones are bent and twisted, some in two or three directions; and the surfaces by which any bone is jointed to the adjacent bones, are invariably oblique with regard to each other.
[Illustration: Fig. 9.]
Take, for instance, the _tibia_, or large bone of the leg, of which a front view and an inner side view are given in the drawings. The tibia is a column transmitting weight from the thigh to the foot; and in any machine of man’s construction a column fulfilling similar purposes would be made straight and of uniform diameter throughout. The bone, on the contrary, does not present the same thickness at any two parts of its length. It has a distinct bend, forwards, in nearly its whole length (fig. 10): there are lateral curves, alternating like those in the letter S, seen along its front (fig. 9): and the articular surface at the lower end is placed obliquely with regard to that at its upper end, in consequence of a twist in the shaft, in such a manner that when the hinder surface of the upper end of the bone rests upon a board, the lower end touches the board only by its outer corner (fig. 10). This disposition of the lower end, I may remark, assists to give the foot a slant outwards from the heel to the toe, so that when we stand, with the heels together, the great toes of the two feet diverge a little from one another.
[Illustration: Fig. 10.]
Moreover, the surfaces by which the tibia is jointed with the thigh-bone at the knee are arranged with a varying degree of obliquity, so that the relation of the leg to the thigh varies somewhat in different positions of the limb. For instance, when we stand upright, the _thigh_ slants _in_wards from the pelvis, and the _leg_ descends in a _vertical_ direction to the ground. While, however, the knee is being bent the leg is carried, not in a vertical plane, but a little obliquely, so that the lower part soon begins to slant _out_wards; and when the knee is fully bent the obliquity of the leg and that of the thigh correspond, and the leg is, as it were, folded up against the thigh. The heel is thus brought up, not to the middle line of the body, but to the hip, and we are enabled to sit with the hips upon the heels, as the Japanese are represented doing, or with one hip upon one heel--a position in which our riflemen are trained to take aim, and in which their predecessors with the arrow were wont to shoot, as is shown by the accompanying sketch of a bowman (fig. 11), taken from one of the Æginetan marbles in the Glyptothek at Munich.
[Illustration: Fig. 11.]
A variety of purposes is attained by the curvilinear shape of the bones and the obliquity in the movements of the joints. Not the least of these is the appearance of elegance and ease which is given to the whole frame, both when it is at rest and when it is in motion. In order that you may fully appreciate this result, I would ask you, the next time you are in a gallery of antique statuary, to contrast the figures which the Egyptians have left us with those by the Greeks. In the former you will find that straight lines and right angles prevail: the figure sits, probably, bolt upright, with the elbows, hips, knees, and ankles bent at right angles: the fingers commonly run straight forwards; and a hand is often laid upon each knee, the limbs of the two sides being quite symmetrically placed. Such statues may be imposing; but they are stiff and unnatural. They represent positions which the body rarely assumes; and they, certainly, are far from pleasing. Very different is the Greek statuary. A correct representation of nature is the great difficulty and the highest consummation of art; and the Greeks evinced their greatness in art by a true appreciation and close imitation of natural form. The position of their figures is life-like; and, therefore, we love to contemplate them. The outline in them exhibits a graceful disposition of curves and obliques; and it is because the great sculptors of Greece were, in this and in other respects, so true to nature that their works have commanded the admiration, and served as models for the imitation, of all succeeding ages.
It is one of the master results of creation, and one of the peculiar marks of creative genius, that _perfection_ and _beauty_ are usually presented together. As truth is the soul of eloquence, so is perfection the soul of beauty. The works of nature are beautiful because there is so much excellence in them, such admirable adaptation to their purpose; and we find the works of man beautiful only so far as they are correct imitations of their great originals in nature, or show some approach to nature’s excellence. And man is the most beautiful object in nature because he is the most perfect, that is, because the purpose of his existence is the highest, and because his physique exhibits the most marvellous moulding to adapt it to its high purpose; because, in short, in him the material is wrought to such a point of refinement as to be the receptacle and minister of the immaterial.
The movements of the three joints between the foot and the leg take place in harmony. The following is the order observed. The raising of the _heel_ is accompanied by a rolling of the foot _in_wards, and by an increased _flexure_ of the plantar arch; and the raising of the _toes_ is accompanied by a rolling of the foot _out_wards and a _straightening_ of the sole.
_The Muscles of the Leg and Foot._
[Illustration: Fig. 12.]
The _first_ series of the movements just described is effected, mainly, by three muscles. Of these one (A, fig. 12) raises the heel while the other two (B, fig. 12, and C, fig. 13) raise and support the ankle. The muscle which acts upon the heel is one of the largest and most powerful in the body; and well it may be, for in raising the heel it has to raise the whole weight of the body. Its fibres, accumulated at the middle and upper part of the leg, form the “calf;” below they taper into a thick tendon (a) connected with the hinder extremity of the heel-bone, and called the _Tendo Achillis_. The name, it need scarcely be said, refers to the tale of Thetis holding her son Achilles by this part when she dipped him in the river Styx. Her hand prevented the part from coming in contact with the water; and so it did not partake of the invulnerability which was conferred upon the rest of his body by the immersion. We read, accordingly, he was finally killed by a wound in the heel[2].
[2] It does not appear that the legend is based upon any peculiar ideas of susceptibility attached to the heel among Eastern nations; nor can the passages in Scripture, that the Serpent shall bruise man’s heel (Genesis iii. 15); “For the greatness of thine iniquity are thy heels made bare” (Jeremiah xiii. 22), be adduced as indicating the existence of such an idea. There are some other myths resembling this one of Achilles; but in them a different part of the body missed the protecting influence. Thus, Ajax was wrapped by Hercules in the skin of the Nemæan lion, and was, thereby, rendered invulnerable, except at the pit of the stomach where the edges of the skin did not quite meet; and he killed himself by running his sword in there. In the _Niebelungenlied_, the hero, Siegfried, is represented to have rendered himself invulnerable by smearing himself with the blood of a dragon which he had killed. A leaf, however, adhering to his back, prevented the contact of the fluid with one spot. The secret was unwarily communicated by his wife Krimhild to his enemy Hagan, who took advantage of the information to plunge his sword into the fatal spot while Siegfried was stooping down to drink at a rivulet.
The lesson inculcated by these myths seems to be that all men, even heroes, have their weak points.
The other two muscles (B and C) also descend from the leg and terminate in tendons (b and c) which pass, one on either side, behind the projections (D and E) which we call respectively the inner and outer ankle, to the inner and outer edges of the instep. They assist to raise the ankle, and support it so as to prevent its swerving from side to side; and they permit it to play to and fro upon them, like a pulley upon ropes running under it, in a safe and easy manner. The inner (b, fig. 12) of the two tendons passes, as before mentioned, beneath the head of the key-bone, and adds greatly to the strength of the arch. It is, moreover, the chief agent in effecting the two movements which are associated with the elevation of the heel, viz. the turning of the sole inward and the flexion of the foot.
[Illustration: Fig. 13.]
The _second_ series of movements--the raising the toes, the turning the sole downwards, and the straightening the foot--are effected by two muscles (F, fig. 12, and G, fig. 13), the tendons (f and g) of which pass, one in front of the inner ankle, and the other in front of the outer ankle, to the respective edges of the instep. These require much less power than their opponents; and the muscles on the front of the leg are, therefore, smaller and weaker than those behind.
A question of practical interest here suggests itself. How is the balance between these antagonistic muscles maintained, and the proper position of the foot preserved? If the muscles which cause the elevation of the heel and the other movements associated with it are so much stronger than those which produce the opposite series of movements, and if, as we know to be the case, muscles are always, even when a limb is at rest, contracting with a certain amount of force, why do not those of superior power gain and maintain the ascendancy, and hold the limb in the position to which they have a tendency to draw it? And why, in this instance, are not the feet kept with the heels raised and the soles inturned and bent? The reply is, that the ill consequence suggested is prevented, and a proper adjustment between the opponent sets of muscles, in this and other parts of the body, is effected through the medium of the nervous system. That system institutes friendly relations, and compels an orderly and harmonious action of the several muscles; and it does so by frequently exerting its influence upon them, keeping them in drill, as it were, and enforcing the habit of yielding in a kindly manner to one another.
[Illustration: Fig. 14. Club-foot.]
You have often observed, and perhaps wondered at, the almost incessant, semi-involuntary and, seemingly, meaningless movements of infants, especially the peculiar sprawlings out of their fingers and toes. Now these are for the purpose of keeping the different sets of muscles in practice and in order, till the will acquires a due control, when they gradually cease. They are going on before birth as well as afterwards; and when they are deficient, or when they take place irregularly, in consequence of an imperfection in the nervous system, the limbs are liable to become deformed. The feet, under these circumstances, are often drawn into the very position I have just mentioned; the sole is turned inwards and upwards, so as never to touch the ground; the heel and the toes are approximated; and the foot rests upon the ground on the outer side, or quite on the fore part, of the instep. Such a condition constitutes one of the most common forms of what is called “club foot.” Children are often born with one or both of their feet thus distorted. Happily, however, if they be submitted in time to the modern improved modes of treatment they may usually be set right. The accompanying woodcut gives a sketch of the foot of a young woman who had not the good fortune to be thus attended to.
The muscles compose the flesh or chief part of the bulk of a limb. The “calf” is almost entirely made up of the fibres of the “calf-muscle.” But at the ankle there are no muscles. As they descend the leg, all the _muscular_ fibres disappear, and there are only _tendons_. These, though much thinner than the muscles, are very strong; and they are the cords or ropes by which the muscles pull upon distant parts. As they pass over the ankle they are strapped down close to the bones by means of stout sinewy cross-bands, which prevent their starting from their places when the muscular portions pull at them.
Two especial advantages result from this arrangement.
_First_, the lower part of the leg and the ankle are reduced in size. Thereby the resistance to the passage of the limb through the air is lessened; and when it is upon the ground, the leg is less in the way of the other foot which is swinging, to and fro, beside it. An elegance of shape is also thereby imparted. The “pretty ankle” owes much of its charm to the mode in which the tendons are disposed. How comparatively thick and clumsy would the ankle be if the tendons of the toes took the straight course represented by the line _a_ in the drawing, instead of being bound down, as they are, to the curve of the ankle!
[Illustration: Fig. 15.]
_Secondly_, the obliquity with which the tendons run to their insertions is increased by this arrangement; and the velocity of the movements to which they minister is increased also. True, a loss of strength is involved in such a disposition, but the gain in velocity is of more importance. If (to refer again to the diagram, fig. 15) the tendon ran in a straight course from the front of the leg to the great toe, the angle at which it joined the toe would enable it to act with more strength; but the movements connected with it could not be so quick as they now are.
We find in the construction of the human frame many instances in which strength is sacrificed to rapidity of movement in this and other ways. Scarcely any conceivable amount of strength, for instance, would be an adequate compensation for a loss of that celerity of movement of the hand which enables us to strike a blow and drive a nail. No wonder, therefore, that strength is here sacrificed to obtain celerity. And the same principle holds good for other parts.
The length and direction of the heel affords a good illustration of the principle of which I am speaking. When the heel-bone runs out to a considerable distance, and nearly straight, behind the ankle, as it does in some of the lower animals and in the inferior races of mankind, it presents a better leverage to the calf-muscle, which is, then, enabled to raise the ankle with a less amount of effort; but there is proportionately less velocity. Accordingly, in the more perfectly formed foot, such as we find it in the higher races of mankind, the heel-bone, instead of running out backwards, descends very obliquely, almost vertically.
In this instance, the loss of strength, which is thus incurred for the purpose of acquiring celerity in movement, is usually compensated for by the greater development of the calf-muscle. Hence the high heel and the well-developed calf go together; and, like most of the other features of good bodily formation, they are, on the whole, best marked in the nations which are endued with the highest intelligence, and which are, in this way, physically, as well as mentally, qualified to occupy the foremost places in the human family. Thus, we may mark a relation between the heel and the brain; and, as the comparative anatomist is able by the inspection of a bone to trace out the skeleton to which it belonged, so might it be possible for the human anatomist, by observing minutely the peculiarities of the heel and the other features of the foot in any particular race of men, to form some estimate of the capacity and conformation of the skull, and thereby, of the amount of intelligence.
Contrast the foot and leg of the EUROPEAN (fig. 16), as represented in the drawing reduced from the Farnese Hercules, with those of the NEGRO (fig. 17), the drawing of which was taken from a native of Sierra Leone. In the former the leg is plump and the calf well developed; the foot is compact and well arched; the heel descends nearly vertically; and the inner ankle stands clearly out and is raised high above the ground. In the Negro the leg is thinner and the calf is not so well defined; the foot is long, flat, and sprawling; the heel is more horizontal; and the inner ankle does not show clearly, and almost touches the ground.
[Illustration: Fig. 16.]
[Illustration: Fig. 17.]
[Illustration: Fig. 18. European.]
[Illustration: Fig. 19. Negro.]
Contrast also the outline (fig. 19) of the foot of the same Negro with that (fig. 18) of an Englishman. Both were traced upon the ground, and reduced upon the same scale. The Negro was 5 ft. 2 in. in height; the Englishman was 6 ft.; both were of the same age: yet the Negro’s foot was considerably the larger. It was 11 inches long, 3-1/2 inches across the middle of the instep, and 10-1/2 inches round the balls of the toes. Whereas the Englishman’s foot was less than 10-1/2 inches long, was 2-1/2 inches across the middle of the instep, and 9-1/2 inches round the balls of the toes. Even in this simple outline how much less shapely is the African’s foot. Some allowance must be made for the fact that the Negro was more accustomed to go barefooted than the Englishman; and the pressure of the boot or shoe has, in some degree, the effect of giving compactness to the foot.