ANATOMY & PHYSIOLOGY A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z                    HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site elbow The hinge joint in the arm made up of parts of the humerus (the upper arm bone) and the ulna and radius bones of the forearm. The ulna forms the part of the joint that allows the hinge motion of the elbow. Part of the radius bone of the forearm (the head of the radius) sits against the humerus and turns to allow the forearm to turn so that the palm is up (pronation) or down (supination). The surface of the elbow joint is covered by articular cartilage that protects and cushions the joints. The large muscle in the back of the arm, the triceps, attaches to the point of the ulna (called the olecranon). When this muscle contracts, it straightens out the elbow. The biceps muscle in the front of the arm, when contracted, bends the elbow. Related category    • ANATOMY AND PHYSIOLOGY Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP