Part 35

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.

Origin.—By three portions: by the internal and external heads, and by the long scapular head. The internal and the external heads are blended except at their proximal extremities. Each head arises from the anconal surface of the shaft of the humerus. The internal head being located toward the deltoid attachment and the external head into the pneumatic fossa. The long head extends from a circumscribed area just posterior to the glenoid cavity of the scapula. The fibers pass around the shoulder-joint, beneath the deltoid.

Insertion.—The broad tendon passes over the elbow-joint and is inserted to the entire under surface of the olecranon of the ulna.

Shape.—Long, large, fleshy.

Relations.—The supraspinatus passes between the internal and the external heads. It is bounded by the biceps and the deltoid.

Action.—An extensor of the antibrachial region directly antagonizing the biceps.

=Brachialis Anticus= (Fig. 15, No. 9; Fig. 14, No. 5). Location.—In the flexure of the humerus and the ulna.

Origin.—It arises fleshy from a circumscribed area on the inner side of the anconal part of the distal extremity of the humerus.

Insertion.—The fibers passing directly over the elbow-joint become inserted to the lateral surface of the proximal end of the ulna close to the margin of the sigmoid cavity.

Shape.—Small, fleshy.

Relations.—With the joint.