14. The leg bends upon the thigh at an angle of about 75 degrees, and the line of the tibia forms, with the sole of the foot, when that is elevated, an angle of 65 degrees.
15. The whole of this limb is susceptible of motion at the hip-joint forwards to a right angle with its perpendicular position; and backwards to an angle of 20 degrees. The leg will then continue to move by itself to its own angle of 75 degrees with the thigh. Its extreme motion does not exceed 45 degrees.
16. When the shoulders are quiescent, the clavicles usually meet in an angle of 110 degrees at the sternum.
17. The utmost elevation of the upper joint of the arm generally forms an angle of 155 degrees with the vertebræ, and about 125 degrees with the line of its clavicle. The flexion of the fore-arm upon its upper part is confined to an angle of nearly 40 degrees.
18. The whole arm is capable of moving forward or outward through nearly 80 degrees, and backward to nearly the same angle with its perpendicular station.
19. The actions of pronation and supination in the hand, range through all intermediate degrees from a horizontal or perpendicular direction to 270 degrees; but 90 degrees of its rotary motion in pronation comes from the shoulder joint.
20. The palm of the hand admits of flexion and extension to 65 degrees in each direction; its lateral motions are 35 outward, and 30 inward. The flexion of the fingers at each phalanx is a right angle.
But it must be observed that in drawing the joints, very considerable difference is found in their length, from inequality of action. The elbow joint, when bent inward, lengthens the arm nearly one eighth; the same general law operates on the knees, fingers, &c. When a man is at rest, and standing on both feet, a line drawn perpendicularly between the clavicles will fall central between his feet. Should he stand on one foot, it falls upon the heel of that foot which supports his weight.
If he raises one arm, it will throw as much of his body on the other side as nature requires to support the equilibrium. One of his legs thrown back brings the breast forward, to preserve the gravity of the figure: the same will be observed in all other motions of the parts to keep the central gravitation in its proper place.
The equipoise of a figure is of two sorts: simple, when its action relates to itself; and compound, when it refers to a second object.