THE POSTERIOR HUMERAL REGION 471 



Nerves. The muscles of this group are supplied by the musculocutaneous nerve. The 

 Brachialis anticus usually receives an additional filament from the musculospiral. 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 Coracobrachialis draws the humerus forward and inward, and at the same 

 time assists in elevating it toward 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 flexed, the Biceps 

 and Brachialis anticus flex the arm upon the forearm, as is seen in efforts at climbing. 



7. The Posterior Humeral Region. 

 Triceps. Subanconeus. 



The Triceps, or the Triceps extensor cubiti (m. triceps brachii) (Fig. 352), 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 is 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 head; and (3) the internal or short 

 humeral head. 



The middle or scapular head (caput longum) 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 muscle 

 fibres pass downward between the two other portions of the muscle, and join 

 with them in the common tendon of insertion. 



The external head (caput laterale) arises from the posterior surface of the shaft 

 of the humerus, between the insertion of the Teres minor and the upper part of 

 the musculospiral groove; from the external border of the humerus and the 

 external intermuscular septum; the fibres from this origin converge toward the 

 common tendon of insertion. 



The internal head (caput mediate) arises from the posterior surface of the shaft 

 of the humerus. below the groove for the musculospiral 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 humerus, and from the back of the whole length of the internal and lower 

 part of the external intermuscular septum. Certain fibres of this portion of the 

 muscle are directed downward to the olecranon, while others converge to the 

 tendon of insertion. 



The tendon of the triceps commences about the middle of the back part of the 

 muscle; it consists of two aponeurotic laminse, one of which is subcutaneous 

 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 receiving the 

 attachment of the muscle fibres, they join above the elbow, and are inserted. 

 for the most part, into the back part of the upper surface of the olecranon process; 

 a band of fibres is, however, continued downward, on the outer side, over the 

 Anconeus, to blend with the deep fascia of the forearm. 



Relations. By its superficial surface, the Triceps is in relation with the Deltoid above; in 

 the rest of its extent it is subcutaneous; by its deep surface, with the humerus, musculospiral 

 nerve, superior profunda vessels, and back part of the elbow-joint. Its middle or long head is in 

 relation, behind, with the Deltoid and Teres minor; in front, with the Subscapularis, Latissimus 

 dorsi, and Teres major. 



The long head of the Triceps descends between the Teres minor and Teres major, dividing 

 the triangular space between these two muscles and the humerus into two smaller spaces, one 

 triangular, the other quadrangular (Fig. 352). The triangular space contains the dorsalis 



