Ulna

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.

The human arm

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.