304 MUSCLES AND FASCIAE. 



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, 

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

 angular processes, and extending, below, to within an inch of the margin of the 

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

 borders. 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 received into an interval between two fleshy slips of 

 the Flexor digitorum profundus. 



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 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 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 supi- 

 nator, 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 EEGION. 

 Triceps. Subanconeus. 



The Triceps 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 the name of the muscle. These three portions have been 

 named, the middle or long head, the external, and the internal head. 



The middle or long 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 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 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 external intermuscular 

 septum ; the fibres from this origin converging 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 

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

 directed, some downwards to the olecranon, whilst others converge to the common 

 tendon of insertion. 



The common tendon of the Triceps commences about the middle of the back 

 part of the muscle ; it consists of two aponeurotic laminae, one of which is sub- 

 cutaneous, and covers the posterior surface of the muscle for the lower half of its 

 extent, the other is more deeply seated in the substance of the muscle. After 



