MUSCLES OF THE ARM 377 



vessels of the arm and by the tendons of the latissimus dorsi, teres major, and 

 subscapularis muscles. In the distal half of the arm they are separated medially 

 by the medial intermuscular septum (described below) and by the medial epicon- 

 dyle and the ulno-volar group of muscles of the forearm. On the lateral side 

 of the arm they are separated by the lateral intermuscular septum, by the 

 lateral epicondyle, and by the brachio-radialis and the extensor muscles of the 

 forearm which take origin from the lateral epicondyle. 



FASCIJE 



The fasciae and the general relations of the muscles of the arm are shown in the cross- 

 sections in fig. .362. 



The tela subcutanea of the arm is fairly well developed and contains a considerable amount 

 of fat, especially near the shoulder. It is but loosely bound to the muscle fascia, except near 

 the insertion of the deltoid, where the union may be more intimate. 



Bursae. — B. subcutanea epicondyli lateralis. — Between the lateral epicondyle and the .skin. 

 Rare. B. subcutanea epicondyli medialis. — Between the medial epicondyle and the skin. 

 Inconstant. B. subcutanea olecrani. — Between the olecranon process of the ulna and the 

 skin. Nearly constant. 



The brachial fascia forms a cylindrical sheath about the muscles of the arm. It contains 

 circular and longitudinal fibres, the former being the better developed. The fascia is strong 

 over the dorsal muscles, especially near the two epicondyles of the humerus. Proximally the 

 fascia of the arm is continued into the axillary fascia and into the fascial investment of the pec- 

 toralis major, deltoid, and latissimus dorsi muscles; distally it is continued into the fa.scial 

 investment of the forearm. It is intimately bound to the epicondyles and to the dorsal surface 

 of the olecranon. It is separated by loose areolar tissue from the bellies of the muscles which it 

 covers. From the tendons of the deltoid, pectoralis major, teres major, and latissimus dorsi 

 muscles, however, fibrous bundles are continued into the brachial fascia. There are a number 

 of orifices in the fascia for the passage of nerves and blood-vessels. Of these, the largest is 

 that for the basilic vein and two or three large branches of the medial antibrachial (internal) 

 cutaneous nerve. This hes on the ulnar margin of the arm in the lower third. On the radial 

 margin he the cephalic vein in a double fold of the fascia, orifices for branches of the musculo- 

 cutaneous nerve, and more dorsally orifices for branches of the radial. From the fa.scia septa 

 descend between the muscles which it invests. Of these septa, the most important are the medial 

 and lateral intermuscular septa, which separate the dorsal group of muscles from the ventral 

 in the distal half of the arm. The medial intermuscular septum is the stronger. It is attached 

 to the medial epicondyle and to the medial margin of the humerus proximal to this. It is 

 continued proximally into the tendon of insertion of the coraco-brachialis and the investing 

 fascia of this muscle. Into it longitudinal bundles of fibres descend from the tendon. It 

 separates the brachialis and pronator teres muscles from the medial head of the triceps. The 

 lateral intermuscular septum is attached to the lateral epicondyle and to the lateral margin 

 of the humerus. It is continued proximally into the dorsal surface of the tendon of insertion 

 of the deltoid muscle, and into the septa laetween the deltoid and the triceps. It separates 

 the triceps from the brachialis in the third quarter of the arm and from the brachio-radi- 

 alis and extensor carpi radialis longus in the distal quarter. The median nerve and brachial 

 vessels lie in front of the medial septum. The ulnar nerve and the superior ulnar collateral 

 (inferior profunda) artery are bound to its dorsal surface. 



MUSCLES 

 1. Dorsal or Extensor Group 



Two muscles are included in this group, the triceps brachii and the anconeus. 

 The triceps is a complex muscle in which proximally three heads, a long or scapu- 

 lar, a lateral humeral, and a medial humeral, may be distinguished. The long 

 head arises from the infraglenoid tuberosity of the scapula, the lateral head from 

 the humerus above and laterally to the groove for the radial nerve ('musculo- 

 spiral groove), the medial head from the lower half and medial margin of the 

 posterior surface of the humerus. Distall^y these heads fuse and are inserted 

 by a common tendon into the olecranon of the ulna. The anconeus lies chiefly 

 in the forearm, but physiologically and morphologically it belongs with the triceps, 

 and hence is described in connection with the muscles of the arm. It is a tri- 

 angular muscle, which arises from the lateral epicondyle and is inserted into the 

 olecranon and adjacent part of the shaft of the ulna. Both muscles are supplied 



