Bones constitute the pressure system of the body. In them are expressed, therefore, laws of architecture, as in the dome of the head, the arches of the foot, the pillars of the legs, etc.; and laws of mechanics, such as the hinges of the elbows, the levers of the limbs, etc.
Ligaments constitute the retaining or tension system, and express other laws of mechanics.
Muscles constitute the contractile or power system; they produce action by their contraction or shortening. In contraction they are lifted and bulged, while in their relaxed state they are flabby and soft. Muscles, attached to and acting on the bony and ligamentous systems, constitute the motion system. In the muscles are expressed, therefore, laws of dynamics and of power.
For instance, for every muscle pulling in one direction, there must be the corresponding muscle pulling in the opposite direction. Muscles are therefore paired, throughout the body. Every muscle on the right side must be paired with one on the left: for every flexor on the front there must be its corresponding extensor on the back.
Muscles express also laws of leverage: they are large in proportion to the length of the lever they move. Those of the individual fingers are small and can fit in between the bones of the hand. They grow larger as we ascend the arm, the leverage being-longer and the weight greater. The muscles of the forearm are larger than those of the fingers; those of the arm larger than those of the forearm, while the muscles of the shoulder are larger still.
Whatever their surface form or markings, they are as masses to he conceived as blocks.
The conception of the figure must begin with the thought of these blocks in their relation to each other. They are to he thought of first as one thinks of the body of a wasp, with only one line connecting them, or without reference at all to connecting portions.
Ideally, in reference to gravitation, these blocks would he balanced symmetrically over each other. But rarely in fact, and in action never, is this the case. In their relations to each other they are limited to the three possible planes of movement. That is, they may be bent forward and back in the sagittal plane, twisted in the horizontal plane, or tilted in the transverse plane. Almost invariably, in fact, all three movements are present, to different degrees.
In these various movements, the limit is the limitation to movement of the spine. The spine is the structure that connects one part of the body with another. It is a strong column occupying almost the centre or axis of the body, of alternating discs of bone and very elastic cartilage. Each segment is a joint, whose lever extends backward to the long groove of the back. Such movement as the spine allows the muscles also allow, and are finally connected by the wedges or lines of the actual contour.
Construction. Masses and Movements of the Body: Tilting of the Masses.
Construction. The Horizontal, Sagittal and Transverse Planes: Tilted and Twisted.
In the hand are four bones, continuous with those of the fingers, called metacarpals (meta, beyond, carpus, wrist). They are covered by tendons on the back, and on the front by tendons, the muscles of the thumb and little finger, and skin pads.
There is a very slight movement like opening a fan between these bones. They converge on the wrist bones and are morticed almost solidly to them. The hand moves with the wrist. The dorsal tendons converge more sharply than the bones.
The short muscles of the hand, crossing only one joint, the knuckle, and moving the fingers individually, lie deep between the metacarpal bones and so are called interossei. They are in two sets, back and front, or dorsal and palmar. The palmar interossei are collectors, drawing the fingers toward the middle finger, and so are fastened to the inner side of each joint except that of the middle finger itself. The dorsal interossei are spreaders, drawing away from the centre, and so are fastened to both sides of the middle finger and to the outside of the other joints. In the thumb and little fingers the muscles of this set are called abductors, and being in exposed positions, are larger. That of the first finger forms a prominent bulge between it and the thumb; that of the little finger forms a long fleshy mass reaching to the wrist.