The distal end of the bone presents a smooth saddle-shaped articular surface, which, in well-marked bones, is divided, when seen from the ventral surface, by a slight nearly median ridge into two unequal portions, lateral and medial (_i_ and _j_). The lateral half is rounded and is called the =capitulum= (_i_). It is broader ventrad than dorsad, and is not continued onto the dorsal surface of the bone. It is for articulation with the proximal end of the radius. The medial half of the surface, the =trochlea= (_j_), is concave and passes directly into the capitular surface laterad, but is limited mediad by a sharp ridge. It is continued onto the dorsal surface of the bone, where it is limited also laterad by a ridge. It articulates with the semilunar notch of the ulna. Proximad of the trochlea the dorsal surface presents a deep fossa, the =olecranon fossa=, which receives the olecranon of the ulna when the arm is straightened. On the ventral surface (Fig. 47) are two shallower fossæ separated by a longitudinal ridge. The one over the trochlea receives the coronoid process of the ulna when the arm is bent, and is called thence the =coronoid fossa= (_l_). The one over the capitulum, the =radial fossa= (_m_), receives a triangular facet on the proximal end of the radius at the same time. Between the radial and coronoid fossæ on one side and the olecranon fossa on the other is only a thin plate of bone. On the medial surface of the distal end is a considerable roughened elevation, the =medial epicondyle= (_n_) (epitrochlea). It gives origin to flexor muscles and to the ulnar collateral ligaments of the elbow-joint. Opposite the medial epicondyle over the capitulum is the =lateral epicondyle= (_o_) for the origin of extensor muscles of the forearm and of the radial collateral ligaments of the elbow-joint. From the lateral epicondyle a ridge, the lateral =supracondyloid ridge= (_p_), continues proximad, curving onto the dorsal surface of the bone and ending about opposite the junction of the deltoid and pectoral ridges. Proximad of the medial epicondyle the bone is pierced near its medial margin by an oblique oval foramen, the =supracondyloid foramen= (_q_). =Radius= (_I_, Figs. 49 and 50).--In the usual position the radius lies with its proximal end on the lateral side of the arm, articulating with the capitulum of the humerus. The proximal end is thus laterad of the proximal end of the ulna. Its distal end, however, lies on the medial side of the distal end of the ulna, so that the radius in the natural position crosses ventrad of the ulna.