The Principle of “Division of Labour”
In this concentration of locomotive power in the foot we have an illustration of what is called the “principle of division of labour,” a principle with which all civilized communities are familiar, and to which we are much indebted for the present advanced state of the arts and sciences; but which we may be said to have borrowed from the economy of nature. We find ever-increasing manifestations of it as we ascend in the animal series, from the lower and more simple to the higher and more complicated forms. Indeed, just as each step in civilization is attended with a further development of this principle, so is each division of the animal kingdom distinguished from those below it by the more distinct assignation of particular functions to particular organs, and by the consequent improvement of the mode in which the functions are performed. While, in proportion as the several organs acquire more distinct speciality in their work, so do they become, more and more, dependent upon one another, and, more and more, subjected to the control of central government, which is represented by the brain.
For instance, some of the lower animals, as the fresh-water Polyp, present nearly a uniform structure throughout their whole substance; and every part of them consequently performs the same function. There is not one organ for digestion, another for circulation, a third for respiration, and so on; but all these functions are performed by the same structure, and are performed, therefore, in a rude and imperfect manner. Any portion of the creature possesses all the requisites for its own nutrition, and is, so, independent of the remainder, and can live alone. Hence, the polyp may be divided into a number of pieces, each of which goes on living. Gradually, as we ascend from these lowly beings to the higher classes of animals, we find organs and functions more and more distinct from another; a Stomach is provided for the work of digestion, a Heart for circulation, Lungs for respiration. Each of these organs is essential to the existence of the others and of every part of the body; and they are all maintained in harmonious co-operation by the presiding influence of the nervous system.
Or, trace one of the functions in illustration of the same principle. Take the function of Locomotion, which has an especial relation to our present subject. In the Leech and the Worm the whole length of the body is occupied in the work, one part as much as another; and still, it is but a crawl. In the Fish the whole body is buoyed up by the water; it is flattened from side to side, and is all, from the head to the tail, concerned in the lateral stroke by which the animal is driven along; the side fins, which are the representatives of limbs, doing little beyond serving to guide and balance. In the other Vertebrates the work of locomotion is so far concentrated as to be assigned, almost entirely, to the limbs. All four limbs are in most of them devoted to it; while the bones and muscles of the trunk are only indirectly concerned in it. In Man, however, two limbs only are assigned to this important office. In him, therefore, the concentration of locomotive power, in other words the principle of division of labour, is carried out to the greatest extent—a disposition which affords one of the many proofs that the construction of his body combines with the faculties of his mind to place him at the head of the animal kingdom.
In making comparisons of different animals with one another, and in speaking of the relative perfection of their several organs, we must not forget that every organ of every animal is perfect as regards the purpose for which it was made. But some animals are said to occupy a higher position than others, or to be superior to others, because their mechanism is more complex, and they are, thereby, enabled to perform a greater variety of functions. And, in the animal kingdom, in proportion as each function rises into prominence, and becomes well and distinctly performed, so is a special organ assigned to it, and that organ becomes more and more highly elaborated.
You will not misunderstand me, then, when I say that concentration of function and perfection of structure usually go together. And, forasmuch as in the lower limbs of man there is a greater concentration of locomotive function than in any other part of any other animal, you will expect to find, in them, a greater perfection of locomotive mechanism—that is to say, a more complete combination of strength with variety, rapidity, and extent of movement—than is elsewhere to be met with.
This consideration will ensure attention while I give a brief account of the anatomy of man’s lower limb, more particularly of the foot.