The ulna is one of the two bones in the forearm and is slightly longer and thinner than the other bone, the radius. It supports the radius and gives the forearm a greater range of motion. The ulna is a long bone, which means it is longer than it is wide and has several layers. The exterior layer is compact bone, which surrounds a layer of spongy, cancellous bone. Beyond that layer is the medullary cavity that contains the bone marrow.
Anatomists use several phrases to describe the location of a body part in relation to the body as a whole. Proximal describes a structure closer to the center of the body. The proximal end of the ulna is the end closest to the elbow, and the head of this bone forms part of the elbow joint. The proximal section has two processes and two notches.
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