. Human physiology : designed for colleges and the higher classes in schools, and for general reading. THE COLLAR-BONES AND THE SHOULDER-BLADES. FIG. 192 HUMAN PHYSIOLOGY. Arrangement of the bones of the forearm for rotary motion. Bones of the hand. shallowness of the socket is the cause of the frequent disloca-tion of the shoulder. But if there were a deep socket like thatin which the head of the thigh-bone is, the arm could not haveany thing like the freeness of motion that it now has. Such anarrangement would involve too much of a sacrifice of necessaryusca for the sake of security. A
. Human physiology : designed for colleges and the higher classes in schools, and for general reading. THE COLLAR-BONES AND THE SHOULDER-BLADES. FIG. 192 HUMAN PHYSIOLOGY. Arrangement of the bones of the forearm for rotary motion. Bones of the hand. shallowness of the socket is the cause of the frequent disloca-tion of the shoulder. But if there were a deep socket like thatin which the head of the thigh-bone is, the arm could not haveany thing like the freeness of motion that it now has. Such anarrangement would involve too much of a sacrifice of necessaryusca for the sake of security. At its lower part the humerusmakes a hinge joint with the forearm. The forearm hastwo bones, the radius, b, Fig. 102, and the ulna, a. The par-ticular arrangement of these two bones is worthy of hinge-like motion of the forearm upon the arm is per-formed by the ulna alone. This bone has a beak-like process,which works over a smooth round surface at the end of thehumerus. It is the outside of this process which you feel atthe point of the elbow. The other bone, the radius, hasnothing to do with this motion. This only rolls on the ulnain the
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