. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 378 HUMAN PHYSIOLOGY. bone; move the leg in as many different directions as possible; notice that it may be flexed or bent; that it may be extended to its original position; that it may be rotated; that it may be moved to and from the midline of the body; that, with the knee held stiff, the whole limb may be made to describe the arc of a circle. These same movements are possible in the leg of a man. This move- ment between bones is obtained by means of joints. If, in the frog, we care- full
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 378 HUMAN PHYSIOLOGY. bone; move the leg in as many different directions as possible; notice that it may be flexed or bent; that it may be extended to its original position; that it may be rotated; that it may be moved to and from the midline of the body; that, with the knee held stiff, the whole limb may be made to describe the arc of a circle. These same movements are possible in the leg of a man. This move- ment between bones is obtained by means of joints. If, in the frog, we care- fully separate the muscles of the thigh to the bone, we find that they are attached to the bone by white, glis- tening tendons. Careful examination shows that the bones themselves are held together by very tough white bands or cords; these are the ligaments. We find, too, that one end of the large thigh bone fits into a socket in the hip bone or pelvic arch. It is thus easy to see how such free movement is obtained in the leg. Ball and Socket Joint. — Such a joint as just described is called a hall and socket joint. In Ball and socket joint. ,i irxT_i • ii.*j" man the movement oi the leg is obtained in ex- actly the way described for the hind leg of the frog. The two best examples of a ball and socket joint are found between the long bone in the arm and the shoulder, and between the bones of the hip and the long bone of the leg. Hinge Joints. — The second kind of joint, in the leg of the frog, is found between the thigh and the shank. Notice that movement here occurs freely in only two directions, backward and forward; hence this is called a hinge joint. In man the best examples of a hinge joint are found in the knee and elbow; others are in the fingers and toes. Gliding Joints. — Another form of joint, best seen in the skeleton of man, is a sliding or gliding joint. Here the range of movement is slight. Gliding joints are found between the vertebrse or bones of the ve
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