388 THE MUSCLES AND FASCIA. 



Relations. Its anterior surface is overlapped above by the Pectoralis major 

 and Deltoid; in the rest of its extent it is covered by the superficial and deep 

 fasciae and the integument. Its posterior surface rests above on the shoulder- 

 joint and upper part of the humerus; below it rests on the Brachialis anticus, 

 with the musculo-cutaneous nerve intervening between the two, and on the 

 Supinator brevis. Its inner border is in relation with the Coraco-brachialis, and 

 overlaps 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 

 anterior surface of the coronoid process of the ulna, being received into an inter- 

 val between two fleshy slips of the Flexor profundus digitorum. 



Relations. 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. The Brachialis anticus usually receives an additional filament from the 

 musculo-spiral. The Coraco-brachialis receives its supply primarily from the 

 seventh cervical, the Biceps and Brachialis anticus from the fifth and sixth 

 cervical nerves. 



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

 at the same time assists in elevating it toAvard the scapula. The Biceps is a 

 flexor of the forearm ; it is also a powerful supinator, and serves to render tense 

 the deep fascia of the forearm by means of the broad aponeurosis given off from 

 its tendon. The Brachialis anticus is a flexor of the forearm, and forms an 

 important defence to the elbow-joint. When the forearm is fixed, the Biceps 

 and Brachialis anticus flex the arm upon the forearm, as is seen in efforts of 

 climbing. 



7. Posterior Humeral Region. 



Triceps. Subanconeus. 



The Triceps (Triceps extensor cubiti) (Fig. 232) 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 on the scapula, 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 



