Like many other bones, the ulna stores minerals and produces blood cells in the bone marrow. However, the primary purpose of the ulna is to support the forearm and allow it to move, according to LearnBones.com. The ulna extends from the elbow to the bones of the wrist and works in conjunction with another long bone in the forearm, called the radius.
According to Healthline, the ulna is about 50 percent larger in diameter than the radius is at four to five months of age. However, over the course of growing and developing, the radius overtakes the ulna in size. By adulthood, the ulna is only about half as thick as the radius. Healthline contends that when the ulna breaks, it usually does so near the wrist or where the ulna and radius fuse to form a stationary joint.
InnerBody.com explains that the ulna is located on the inside of the arm, when the palms are held up. In other words, it is on the side of the arm that holds the pinky, while the radius is on the side that holds the thumb.
LearnBones.com states that the ulna is slightly curved, as are the other bones in the arm. Many different muscles and tendons attach to the ulna to permit movement in the arm, wrist and hand.