Ulna

The human arm

The ulna is one of the two bones which make up the lower forearm in tetrapods. The other one is the radius. Above them is the elbow and humerus; below are the hands or front feet.

When the forearm is in its normal anatomical position, the ulna—a long bone that extends from the elbow to the wrist—is located on the medial side. It narrows as it gets closer to the wrist and widens near the elbow. The olecranon process, a bony bone at the elbow, resembles a hook and inserts into the humerus's olecranon fossa. This creates a hinge joint with the humeral trochlea and avoids hyperextension. Additionally, there is a radial notch for the ulnar tuberosity, which muscles attach to, and the head of the radius.

Ulna Media

Proximal extremity of left ulna. Lateral aspect.
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The ulna is formed into bone from three centres, shown here.
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Bones of left forearm. Anterior aspect.
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The radius and ulna of the left forearm, posterior surface.
Quill knobs on the ulnae of fossil (top) and modern (bottom) birds.
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Vertical section through the articulations at the wrist, showing the synovial cavities.
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Bones of left forearm. Anterior aspect.
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Bones of left forearm. Posterior aspect.
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Ligaments of wrist. Anterior view
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Ligaments of wrist. Posterior view.
Ulna Anatomy by Jason Christian.webm

Ulna Anatomy, by Jason Christian.