270 



APPLIED ANATOMY. 



firmly held in place by the transverse humeral ligament. Pus, in finding an exit 

 from the joint, follows the long tendon of the biceps and passes under the transverse 

 humeral ligament, then beneath the tendon of the pectoralis major to appear on the 

 anterior aspect of the arm at its lower border. Luxation of the tendon outwardly 

 would be opposed by the insertion of the pectoralis major, therefore it is only dis- 

 placed inwardly. Rupture of the long tendon may occur from violent muscular con- 

 traction; or, in rheumatoid arthritis of the shoulder, the tendon may become partly 

 dissolved and break. When this occurs the belly of the muscle contracts and forms 

 a large protuberance on the front of the arm (Fig. 281). 



The short head of the biceps fuses with the coracobrachialis muscle, to be 

 attached with it to the coracoid process on its outer portion. The pectoralis minor is 



the third muscle attached to this process. 

 The biceps forms the large muscular 

 swell on the front of the arm between 

 the anterior fold of the axilla and elbow. 

 At its lower end the biceps inserts by a 

 strong tendon into the posterior border 

 of the bicipital tubercle of the radius. 

 An example of its rupture is shown in 

 Fig. 282. Between it and the bone is 

 a bursa, which does not communicate 

 with the elbow-joint. The bicipital fas- 

 cia is given off from the tendon and 

 passes downward and inward to blend 

 with the deep fascia covering the flexor 

 group of mus'cles. The biceps not only 

 flexes the radius on the arm but also acts 

 as a powerful supinator. 



The brachialis anticus covers 

 the lower three-fifths of the humerus 

 and begins with two slips, one on each 

 side of the insertion of the deltoid ten- 

 don. It inserts into the inner and lower 

 part of the anterior surface of the coro- 

 noid process of the ulna. As the articu- 

 lation of the ulna and trochlear surface 

 of the humerus is a pure hinge-joint the 

 muscle acts solely as a flexor. 



THE POSTERIOR OR EXTENSOR SET. 

 The posterior or extensor set in- 



rio. 282. mapture or me lower tenaon 01 tne oiceps. i \ ,\ . j ,1 u 



Contraction of the muscle produces a swelling abnormally eludes the triceps and the SUbancOnCOUS, 



high up on the arm. (From a photograph.) when present as a distinct muscle. 



The Triceps Muscle. The mus- 

 cular mass on the posterior surface of the arm is formed solely by the triceps muscle. 

 It arises by three heads and inserts by a single tendon into the olecranon process of 

 the ulna. Its three heads are the long, external, and internal. The long head arises 

 from the lower edge of the glenoid cavity and the scapular border below it for 2.5 

 cm. (i in.). It blends with the capsule of the joint and tends to strengthen it at 

 this point. When the arm is abducted, this tendon is closely applied to the capsule 

 and head of the humerus, and when the head escapes in luxation, it slips out anterior 

 to the tendon. The external head arises from the humerus above the musculospiral 

 groove and from the external intermuscular septum; the internal head arises from 

 the humerus below the musculospiral groove and from the internal and the lower 

 part of the external intermuscular septum (Fig. 283). 



At its lower end the triceps inserts into the olecranon process, the upper third 

 of the ulna, and the deep fascia of the back of the forearm. The expansion of fascia 

 from the olecranon on the inner side is thin and insignificant, but that on the outer 

 side, on the contrary, is thick and strong, and when fracture of the bone occurs is an 

 important factor in preventing separation of the fragments. 



FIG. 282. Rupture of the lower tendon of the biceps. 



