The ulna is a long tapering bone, united by ossification to the outer and posterior surface of the radius. Its superior extremity is of considerable length and thickness, and projects from the head of the radius in an upward and backward direction. This is the elbow or olecranon process. In front it presents a smooth surface, which articulates with the groove between the condyles of the humerus, and also a hooked projection forward termed the beak.