Page:Popular Science Monthly Volume 29.djvu/688

670 saving of needless expenditure of force and energy which Dame Nature practices. The study of human anatomy, which of course is one in many points with the comparative science as applied to lower life, reveals not a few instructive examples of this saving tendency in life's ways. The human head, for example, is nicely balanced on the spine. Compared with heads of lower type, this equipoise forms a prominent feature of man's estate. The head-mass of dog, horse, or elephant requires to be tied on, as it were, to the spine. Ligaments and muscular arrangements of complex nature perform their part in securing that the front extremity of these forms should be safely adjusted. But in man there is an absence of effort apparent in Nature's ways of securing the desired end. The erect posture, too, is adjusted and arranged for on principles of neat economy. The type of body is the same as in lower life. Humanity appears before us as a modification, an evolution, but in no sense a new creation. Man rises from his "fore-legs"—arms being identical, be it remarked, with the anterior pair of limbs in lower life—and speedily there ensues an adaptation of means to ends, and all in the direction of the economical conversion of the lower to the higher type of being. The head becomes balanced, and not secured, as we have seen, and thus a saving of muscular power is entailed. Adjustments of bones and joints take place, and the muscles of one aspect, say the front, of the body, counterbalance the action of those of the other aspect, the back; and between the two diverging tendencies the erect position is maintained practically without effort. So, also, in the petty details of the work, Nature has not been unmindful of her "saving clause." We see this latter fact illustrated in the disposition of the arrangements of foot and heel. One may legitimately announce that man owes much to his head; but the truth is he owes a great deal of his mental comfort and physical economy to his heels. The heel-bone has become especially prominent in man when compared with lower forms of quadruped life. It projects far behind the mass of foot and leg, and thus forms a stable fulcrum or support, whereon the body may rest. Here, again, economy of ways and means is illustrated. There is no needless strain or active muscular work involved in the maintenance of the erect posture in man. It is largely a matter of equipoise, wrought out through a scheme of adaptation which takes saving of power and energy as its central idea.

Physiological research lays bare many other points in human and allied life which bear out the contention and principle that natural economics is a powerful and prevailing reality of life. Muscles are ordered, for example, on the plain principle of single acts and of divided tasks. Thus a man bends his forearm on the upper arm largely by aid of the familiar "biceps." This done, the "biceps" retires from the field of work. The arm is straightened by the action of a different muscle, the "triceps." So, also, with the shutting and