378 THE MUSCULAK SYSTEM. 



elevators of the shoulder girdle. Again, in forward and backward movements at the shoulder- 

 joint, great assistance is derived from muscles acting directly on the shoulder girdle pectoralis 

 minor and serratus anterior ; trapezius and rhomboidei. 



2. In relation to the trunk and limbs, the shoulder muscles, by fixing the humerus, have 

 auxiliary .power on the one hand in movements of the trunk, such as forced inspiration ; on the 

 other hand, acting along with muscles fixing the elbow-joint, they stiffen the limb so as to 

 permit of the more refined movements of the wrist and fingers. 



FASCI/E AND MUSCLES OF THE ARM. 



FASCIAE. 



.The superficial fascia presents no features of importance. There is a bursa 

 beneath it over the olecranon, and occasionally another over the medial epicondyle 

 of the humerus. 



The deep fascia forms a strong tubular investment for the muscles on the 

 anterior and posterior aspects of the humerus. It is continuous above with the 

 deep fascia of the shoulder and axilla, and is further strengthened by fibres derived 

 from the insertions of the pectoralis major, latissimus dorsi, and deltoid muscles. 

 At the elbow it becomes continuous with the deep fascia of the forearm, and 

 gains attachment to the epicondyles of the humerus and the olecranon of the ulna ; 

 it is strengthened also by important bands associated with the insertions of the 

 biceps anteriorly and the triceps posteriorly, to which reference will be made in 

 the account of these muscles. 



About the middle of the arm on the medial side, the deep fascia is per- 

 forated for the passage of the basilic vein and the medial cutaneous nerve of the 

 forearm. 



The intermuscular septa are processes of the deep fascia attached to the 

 epicondylic ridges of the humerus. The medial and stronger septum is placed 

 between the brachialis muscle anteriorly and the medial head of the triceps 

 posteriorly, and gives origin to both. It extends proximally to the insertion 

 of the coracobrachialis (which is often continued into it), and the ulnar nerve 

 and superior ulnar collateral vessels pass distally over its medial edge. The lateral 

 septum is thinner. It separates the brachialis muscle and brachioradialis in front 

 from the medial and lateral heads of the triceps behind, and gives origin to 

 those muscles. It extends proximally to the insertion of the deltoid, and is 

 pierced by the radial nerve and profunda brachii vessels. . 



MUSCLES OF THE ARM. 



The muscles of the arm comprise the biceps, coracobrachialis, and brachialis 

 on the anterior aspect, and the triceps brachii on the posterior aspect of the 

 humerus. Except at its extremities, the biceps brachii is superficial, and forms a 

 rounded fleshy mass on the anterior aspect of the arm. The coracobrachialis is 

 visible on its medial side in the proximal half of the arm, particularly when the 

 arm is raised. The brachialis is concealed by the biceps. The triceps brachii forms 

 the thick mass of muscle covering the posterior surface of the humerus. 



M. Coracobrachialis. The coracobrachialis is a rudimentary muscle. It 

 arises under cover of the deltoid from the tip of the coracoid process, by fleshy 

 fibres, in common with the short head of the biceps, and also frequently from 

 the tendon of insertion of the pectoralis minor muscle. 



The fleshy belly is pierced by the musculo-cutaneous nerve, and ends in a flat 

 tendon which is inserted into a faint linear impression about an inch in length on 

 the middle of the medial border of the body of the humerus (Fig. 336, p. 376). It 

 is often continued into the medial intermuscular septum. 



The coracobrachialis is the remains of a threefold muscle, of which only two elements are 

 usually present in man, but of which in anomalous cases all the parts may be more or less fully 

 developed. The passage of the musculo-cutaneous nerve through the muscle is an indication of 

 its. natural separation into two parts, which represent the persistent middle and distal elements. 



