Ulna is one of the two bones (the radius is the other) of the antebrachium (forearm). The upper end of the ulna forms the point of the elbow, or olecranon, which becomes more prominant on the surface as the elbow is bent. In the horse, only the upper portion of the ulna is present; its lower end tapers to a point. In the horse, the ulna is fused back to the radius. In the dog and cat, the ulna extends down to the wrist and is not fused to the radius. Ulna is the longest bone of the dog's body.