THE POSTERIOR HUMERAL REGION. 477 



humerus. from which it is separated by the Subscapularis, Teres major, Latissimus 

 dorsi, Brachialis anticus. and the musculo-cutaneous nerve. Its inner border is 

 in relation with the Coraco-brachialis. the brachial vessels, and median nerve ; its 

 outer border, with the Deltoid and Supinator longus. 



The Brachialis anticus is a broad muscle, which covers the elbow-joint and 

 the lower half of the front of the humerus. It is somewhat compressed from 

 before backward, and is broader in the middle than at either extremity. It arises 

 from the lower half of the outer and inner surfaces of the shaft of the humerus, 

 and commences above at the insertion of the Deltoid, which it embraces by two 

 angular processes. Its origin extends below, to within an inch of the margin of 

 the articular surface, and is limited on each side by the external and internal 

 borders of the shaft of the humerus. It also arises from the intermuscular septa 

 on each side, but more extensively from the inner than the outer, from which it is 

 separated below by the Supinator longus and Extensor carpi radialis longior. Its 

 fibres converge to a thick tendon, which is inserted into a rough depression on the 

 inferior surface of the coronoid process of the ulna, being received into an interval 

 between two fleshy slips of the Flexor digitorum profundus. 



Eelations. By its anterior surface* with the Biceps, the brachial vessels, 

 musculo-cutaneous, and median nerves ; by its posterior surface, with the 

 humerus and front of the elbow-joint ; by its inner border, with the Triceps, ulnar 

 nerve, and Pronator radii teres, from which it is separated by the intermuscular 

 septum : by its outer border, with the musculo-spiral nerve, radial recurrent 

 artery, the Supinator longus. and Extensor carpi radialis longior. 



Nerves. The muscles of this group are supplied by the musculo-cutaneous 

 nerve, but the nerve to the Coraco-brachialis is often an independent branch of 

 the outer cord of the Brachial plexus. The Brachialis anticus usually receives 

 an additional filament from the musculo-spiral. 



Actions. The Coraco-brachialis draws the humerus forward and inward, and 



ita in elevating it. The Biceps is a flexor of the forearm : it is also a supinator, 

 and makes tense the deep fascia of the forearm by means of the bicipital fascia. 

 The Brachialis anticus is a flexor of the forearm, and protects the elbow-joint. 

 When the forearm is fixed, the Biceps and Brachialis anticus flex the arm, as is 

 seen in efforts of climbing. 



Posterior Humeral Region. 

 Triceps. Subanconeus. 



The Triceps ( Triceps extemor cubiti) (Fig. 305) is situated on the back of the 

 arm. extending the entire length of the posterior surface of the humerus. It is of 

 large size, and divided above into three parts; hence its name. These three 

 portions have been named (1) the middle, scapular, or long head ; (2) the external, 

 or long humeral ; and (3) the internal, or short humeral head. 



The middle or scapular head arises, by a flattened tendon, from a rough 

 triangular depression immediately below the glenoid cavity, being blended at its 

 upper part with the capsular ligament : the muscular fibres pass downward 

 between the two other portions of the muscle, and join with them in the common 

 tendon of insertion. 



The external head arises from the posterior surface of the shaft of the humerus, 

 between the insertion of the Teres minor and the upper part of the musculo-spiral 

 groove; from the external border of the humerus and the external intermuscular 

 septum : the fibres from this origin converge toward the common tendon of 

 insertion. 



The internal head arises from the posterior surface of the shaft of the humerus, 

 below the groove for the musculo-spiral nerve ; commencing above, narrow and 

 pointed, below the insertion of the Teres major, and extending to within an inch 

 of the trochlear surface : it also arises from the internal border of the humerus 

 and internal intermuscular septum. The fibres of this portion of the muscle are 



