a, head; b, greater tuberosity; c, lesser tuberosity; d, bicipital groove; e, pectoral ridge; f, deltoid ridge; g, rough area for insertion of latissimus dorsi and teres major; h, nutrient foramen; i, capitulum; j, trochlea; l, coronoid fossa; m, radial fossa; n, medial epicondyle; o, lateral epicondyle; q, supracondyloid foramen.
Along the lateral border of the proximal end of the shaft is a high rough ridge semicircular in side view, the great tuberosity (b). It gives attachment to muscles and is marked on its dorsal border by a deep depression for the tendon of the infraspinatus muscle. On the medial margin of the proximal end closely associated with the head is a smaller elevation, the lesser tuberosity (c), also for muscular attachment.
Between the greater and lesser tuberosities on the ventral surface is seen a broad groove, the sulcus intertubercularis or bicipital groove (d), which passes distad onto the surface of the shaft. In the natural state it is converted into a canal by overlying tendons and lodges the tendon of the biceps muscle.
The shaft is nearly cylindrical at its middle, but its dorsoventral diameter is slightly greater than its mediolateral diameter. Its proximal end is flattened mediolaterad, while its distal end is flattened dorsoventrad.
From the ventral margin of the greater tuberosity a ridge, the pectoral ridge (e), is continued onto the surface of the shaft, and from the dorsal margin another ridge, the deltoid ridge (f), passes distad and ventrad so as to meet the pectoral ridge near the middle of the ventral surface of the bone. On the medial margin of the bone near the junction of the first and second fourths is a roughened area (g) for the attachment of the tendons of the latissimus dorsi and teres major muscles, and on the same surface near the junction of the second and last thirds is a nutrient foramen (h).
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).