Ulna

The ulna is the longer of the two bones of the forearm; the other being the radius. When the palm faces forward, the ulna is the inner bone (the one nearest the body) running down the forearm parallel to the radius. The upper end joins with the radius and extends into a rounded projection that fits around the lower end of the humerus (the upper arm bone) to form the elbow joint. The lower end of the ulna is rounded and forms a joint with the wrist bones and lower end of the radius.