Fig. 9.
Continuing to descend, we come to a sort of hollow basin, the pelvis, which seems merely to contain, rather than protect, the abdominal organs: the intestines, kidneys, etc. Such a structure seems to be in accord with the minor physiological importance of these organs, whose function (digestion) is periodic and may be temporarily suspended, in defiance of physiological stimuli, without suspension of life. In the lower part of the skeleton, on the contrary, the arrangement between the soft and bony tissues is inverted: the long bones of the limbs constitute the inner part; and they are covered over with thick, striped muscles, organs of mechanical movement for the purpose of locomotion. Here the function of the skeleton is exclusively that of support, and in its mechanism it represents a series of levers.
Accordingly, the structure of the skeleton also shows us how the stature is composed of parts that differ profoundly in their physiological significance; life as a complete whole, the living man, is contained within the bust, which holds the organs of the individual, vegetative life; those of life in relation to its environment, and those of life in relation to the race, namely, the organs of reproduction.
Deprived of arms and legs, man could still live; the limbs are nothing more than appendages at the service of the bust, in all animals; they serve to transport the bust, that is, the part which constitutes the real living animal, which without the limbs would be as motionless as a vegetable, unable to go in pursuit of nourishment or to exercise sexual selection.
The embryos of different animals, of a dog, a bat, a rabbit and of man (as may be seen in Fig. 11) show that the fundamental part of the body is the spinal column, which limits and includes the whole animal in the process of formation.
If we next examine the embryonic development of man, as shown in Fig. 13, we may easily see how the limbs develop, at first as almost insignificant appendages of the trunk, remaining hidden within the curve of the spinal column; and even in an advanced stage of development (15th week), they still remain quite accessory parts in their relation to the whole.
Having established these very obvious principles, we may ask ourselves: of two men of equal stature, which is physiologically the more efficient? Evidently, that one of the two who has the shorter legs.
In other words, it is of fundamental importance to determine the reciprocal relation, in the stature, between the bust and the lower limbs, that is, between the height of the bust and the total height of the body.
Fig. 10.—Gastrula of a sponge.