382 MUSCLES AND FASCIJE. 



humerus, from which it is separated by the Subscapularis, Teres Major, Latis- 

 simus 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 em- 

 braces 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 ex- 

 ternal 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. Its fibres converge to a thick tendon, which is inserted into a rough 

 depression on the under surface of the coronoid process of the ulna, being re- 

 ceived into an interval between two fleshy slips of the Flexor Digitorum Pro- 

 fundus. 



Relations. By its anterior surface, with the Biceps, the brachial vessels, mus- 

 culo-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 Eadii 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. 



Actions. The Coraco-brachialis draws the humerus forwards, and inwards, 

 and at the same time assists in elevating it towards the scapula. The Biceps 

 and Brachialis Anticus are flexors of the forearm ; the former muscle is also 

 a supinator, and serves to render tense the fascia of the forearm by means of 

 the broad aponeurosis given off from its tendon. When the forearm is fixed, 

 the Biceps and Brachialis Anticus flex the arm upon the forearm, as is seen in 

 efforts of climbing. The Brachialis Anticus forms an important defence to the 

 elbow-joint. 



POSTERIOR HUMERAL REGION. 

 Triceps. Subanconeus. 



The Triceps (Fig. 238) 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, trian- 

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

 upper part with the capsular and glenoid ligaments ; the muscular fibres pass 

 downwards 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 hume- 

 rus, between the insertion of the Teres Minor and the upper part of the mus- 

 culo-spiral groove, from the external border of the humerus and the external 

 intermuscular septum : the fibres from this origin converge towards 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 hu- 

 merus and internal intermuscular septum. The fibres of this portion of the 



