The longer of the 2 bones of the forearm; the other is the radius. With the arms straight at the sides, palm forwards, the ulna is the inner bone (that is, nearer the trunk) running down the forearm on the side of the little finger. The upper end of the ulna articulates with the radius and extends into a rounded projection (known as the olecranon process) that fits around the lower end of the humerus to form part of the elbow joint. The lower end of the ulna articulates with the carpals ( wrist bones) and lower part of the radius.


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