The human forearm has two large bones stretching from the elbow joint to the wrist joint: the ulna and the radius. The latter, sometimes called the radial bone, starts on the lateral side of the elbow and reaches the thumb side of the wrist. At the elbow, the radius connects with the capitulum of the humerus. At the radial notch, it connects to the ulna. At the wrist, it and the ulna connect again and form the wrist joint.
The radius is a long bone, meaning it is longer than it is wide. It is shorter and smaller than the ulna and is composed of a shaft or body and two extremities. Within the shaft is the long and narrow medullary cavity, around which is a strong layer of compact bone. The medullary cavity contains yellow bone marrow with walls of spongy bone. The marrow helps store energy for the body as triglycerides. At both extremities of the radius, spongy bone columns help provide strength in the medullary cavity.
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