_Action._—When the scapula is fixed it is a muscle of inspiration. When the ribs are fixed, it draws the scapula downward. =Subscapularis.= _Location._—Scapulo-humeral region. _Origin._—From the anterior and outer half of the scapula. _Insertion._—By a strong and subcylindrical tendon to the top of the ulnar tuberosity of the humerus close to the combined tendons of the coraco-brachialis and teres minor. _Shape._—A large and powerful muscle. _Relations._—The flat tendon of the thoraco-scapularis divides the posterior portion of the belly into two portions. _Action._—A powerful rotary muscle of the head of the humerus; aids in keeping the humeral head in the glenoid cavity. THE MUSCLES OF THE BRACHIAL REGION Biceps Triceps Deltoid Brachialis anticus =Biceps= (Fig. 13, No. 8). (Synonym.—Biceps brachii.) _Location._—The anterior brachial region. _Origin._—By a broad tendon it covers the top of the shoulder-joint, dividing into two heads, giving rise to the long and the short heads. The long is inserted into the outer part of the head of the coracoid just beyond the glenoid cavity; the short head to the distal angle of the ulnar tuberosity of the humerus. _Insertion._—To the ulna just in front of the articular cavity for the trochlear surface of the distal extremity of the humerus. _Shape._—Large, subfusiform. _Relations._—On one side by the triceps and the other the deltoid and anteriorly partially covered by the patagii muscles. _Action._—A powerful flexor of the forearm. =Deltoid= (Fig. 13, No. 12; Fig. 15, No. 8). _Location._—Occupying the lateral side of the humerus; the brachial region. _Origin._—Divided into two portions, the long narrow head extends from the clavicular process of the scapula and from the adjacent surface of the same bone. These fibers then extend around the back of the shoulder-joint, and are joined by the fibers that arise from the entire outer surface of the large os humero-scapulare. These latter fibers are inserted upon an extensive area upon the anconal part of the bone beyond the humeral articular head, and to almost the entire shaft below it. _Insertion._—By a subcylindrical tendon to the proximal side of the tubercle of the external condyle, and above the insertion of the extensor metacarpi radialis longus. _Shape._—Large, fleshy, with tendinous attachment. _Relations._—On one side by the biceps and the other by the triceps also the patagii. _Action._—To extend the arm. =Triceps= (Fig. 15, No. 7). (Synonym.—Triceps brachii.) _Location._—The posterior humeral region.