THE UPPER ARM. 77 



Although almost the entire capsule is surrounded and strengthened by the insertions of muscles, 

 this place is not covered by any muscle, and through it occurs the dislocation which is second 

 in frequency, the subglenoid or axillary dislocation. 



A large bursa, which does not communicate with the joint, is also situated beneath the 

 deltoid muscle (subdeltoid bursa) and may extend beneath the acromion. This bursa, when 

 diseased, may be mistaken for an effusion into the shoulder- joint. The capsular ligament 

 possesses but one important strengthening band, the coracohumeral ligament, which arises from 

 the outer edge of the coracoid process and radiates in the capsule toward the greater tuberosity 

 of the humerus. The joint is well protected above by the strong coracoacromial ligament, which 

 extends from the acromion to the posterior surface of the coracoid process. It prevents the head 

 of the bone from slipping upward, this displacement being possible only when a fracture of the 

 overhanging acromion is present. 



THE UPPER ARM. 



Upon the anterior or flexor surface of the arm the prominence of the biceps muscle may be 

 easily palpated; to either side of this prominence are the outer and inner bicipital grooves respec- 

 tively [indicating the inner and outer edges of this muscle. The term "bicipital groove" is 

 usually applied by English authors to the bony groove in the humerus which contains the 

 long tendon of the biceps. ED.]. The pulsations of the brachial artery may be palpated at the 

 inner margin of the muscle. The bicipital prominence becomes more pointed as it passes 

 upward, and finally disappears beneath the edge of the pectoralis major muscle at the so-called 

 anterior axillary fold. This portion corresponds to the short head of the biceps and to the 

 coracobrachialis muscles. High up to its inner side may be seen, or at least felt, the pulsations 

 of the axillary artery. This is the place of election for the ligation of this vessel (see page 73). 

 In the upper portion of the internal bicipital groove the chief branches of the brachial plexus 

 accompany the artery and may be palpated for a varying distance downward into the arm. 



The comparatively thin deep fascia of the arm sends off the external and internal inter- 

 muscular septa, which are attached to the external and internal condyloid ridges respectively and 

 extend downward as far as the epicondyles. They separate the biceps, brachialis anticus, and 

 coracobrachialis muscles, which are situated anteriorly, from the posterior extensor mass of the 

 triceps muscle. The biceps muscle arises by a long head from the supraglenoid tubercle within 

 the shoulder- joint (see page 76), and by a short head from the apex of the coracoid process; it 

 inserts into the tuberosity of the radius. The brachialis anticus muscle, situated beneath the biceps, 

 arises from the anterior aspect [i. e., inner and outer surfaces. ED.] of the humerus, below the 

 insertion of the deltoid muscle, and from the intermuscular septa, and is inserted into the coronoid 

 process of the ulna. The origin of the coracobrachialis muscle is from the coracoid process in 

 common with the short head of the biceps, and its insertion is at about the middle of the internal 

 border of the humerus. The long head of the triceps arises from the infraglenoid tubercle of the 

 scapula; the inner head arises from the posterior surface of the humerus below the musculospiral 

 groove; the outer head commences above the musculospiral groove, which it bridges over, and 

 arises from the outer surface of the bone and from the external intermuscular septum. These 

 three heads are inserted into a common tendon which is attached to the olecranon. 



