212 



OSTEOLOGY 





the fibers of the tendon of insertion of the Coracobrachialis; its lower part is 

 smooth, concave from above downward, and gives origin to the Brachialis. 1 



The posterior surface appears somewhat twisted, so that its upper part is 

 directed a little medialward, its lower part backward and a little lateralward. 

 Nearly the whole of this surface is covered by the lateral and medial heads of 

 the Triceps brachii, the former arising above, the latter below the radial 

 sulcus. 



The Lower Extremity. The lower extremity is flattened from before backward, 

 and curved slightly forward; it ends below in a broad, articular surface, which is 

 divided into two parts by a slight ridge. Projecting on either side are the lateral 

 and medial epicondyles. The articular surface extends a little lower than the 

 epicondyles, and is curved slightly forward; its medial extremity occupies a lower 

 level than the lateral. The lateral portion of this surface consists of a smooth, 

 rounded eminence, named the capitulum of the humerus ; it articulates with the cup- 

 shaped depression on the head of the radius, and is limited to the front and lower 

 part of the bone. On the medial side of this eminence is a shallow groove, in which 

 is received the medial margin of the head of the radius. Above the front part 

 of the capitulum is a slight depression, the radial fossa, which receives the anterior 

 border of the head of the radius, when the forearm is flexed. The medial portion 

 of the articular surface is named the trochlea, and presents a deep depression be- 

 tween two well-marked borders; it is convex from before backward, concave from 

 side to side, and occupies the anterior, lower, and posterior parts of the extremity. 

 The lateral border separates it from the groove which articulates with the margin 

 of the head of the radius. The medial border is thicker, of greater length, and 

 consequently more prominent, than the lateral. The grooved portion of the artic- 

 ular surface fits accurately within the semilunar notch of the ulna; it is broader and 

 deeper on the posterior than on the anterior aspect of the bone, and is inclined 

 obliquely downward and forward toward the medial side. Above the front part 

 of the trochlea is a small depression, the coronoid fossa, which receives the coronoid 

 process of the ulna during flexion of the forearm. Above the back part of the troch- 

 lea is a deep triangular depression, the olecranon fossa, in which the summit of the 

 olecranon is received in extension of the forearm. These fossa? are separated from 

 one another by a thin, transparent lamina of bone, which is sometimes perforated 

 by a supratrochlear foramen; they are lined in the fresh state by the synovial 

 membrane of the elbow-joint, and their margins afford attachment to the anterior 

 and posterior ligaments of this articulation. The lateral epicondyle is a small, 

 tuberculated eminence, curved a little forward, and giving attachment to the radial 

 collateral ligament of the elbow-joint, and to a tendon common to the origin of 

 the Supinator and some of the Extensor muscles. The medial epicondyle, larger 

 and more prominent than the lateral, is directed a little backward; it gives attach- 

 ment to the ulnar collateral ligament of the elbow-joint, to the Pronator teres, 

 and to a common tendon of origin of some of the Flexor muscles of the forearm; 

 the ulnar nerve runs in a groove on the back of this epicondyle. The epicondyles 

 are continuous above with the supracondylar ridges. 



Structure. The extremities consist of cancellous tissue, covered with a thin, compact layer 

 (Fig. 209) ; the body is composed of a cylinder of compact tissue, thicker at the center than toward 

 the extremities, and contains a large medullary canal which extends along its whole length. 



