This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
Such a joint as that at the hip is called a ball and socket joint, and allows of a greater variety of movement than any other kind. Through movements taking place at it the thigh can (1) be flexed, that is, bent so that the knee approaches the chest, and (2) extended or straightened again; it can (3) be abducted so that the knee is moved away from the middle line of the body, and (4) adducted or brought back again; by movement at the hip the limb can also (5) be circumducted, so that, with knee and ankle joints held rigid, the whole leg is made to describe a cone, of which the apex is at the hip-joint and the base at the foot; and finally (6) rotated so that the whole limb can be rolled to and fro a little about its own long axis. All ball and sockets joints allow all these movements to a greater or less extent.
Is there in health any definite space between the bones of the hip-ioint? What is the chief use of the ligaments? How are the bones held together? What in addition to muscles helps to keep the bones of the joint in contact? Describe an experiment illustrating the effect of atmospheric pressure in keeping the bones together?
What essential parts are found in all joints?
What is such a joint as the hip-joint called?
* The structure of joints can be readily seen in those of a fresh calf's or sheep's foot. The synovial membrane is so thin and so closely adherent to the parts it lines that a microscope is needed for its demonstration; but all the other parts are readily made out.
Another important ball and socket joint is that between the upper end of the humerus and the hollow (glenoid fossa) near the upper outer corner of the shoulder blade. The glenoid fossa being much shallower than the acetabulum the range of movement possible at the shoulder, is greater than at the hip-joint.