The Movements of the Foot
We come now to the Movements of the foot upon the leg; and rarely do we contemplate anything more calculated to excite our admiration. Consider their variety, the rapidity with which they take place, in order to effect the requisite succession of positions in walking and running, and to adapt the sole to the inequalities of the surface on which we tread; and remember the great weight which has to be sustained while these movements are going on: yet, how seldom is there a failure.
This combination of variety of movement with security is effected by the employment of three joints, each of which plays in a direction different from the others, while all act harmoniously together.
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.
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.
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 inwards 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 outwards; 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.
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 inwards, and by an increased flexure of the plantar arch; and the raising of the toes is accompanied by a rolling of the foot outwards and a straightening of the sole.