204 LATERAL THORACIC REGION. 



axillary vessels and nerves, and in it the subclavian artery is tied 

 below the clavicle. 



The Subclavius muscle arises by a round tendon from the cartilage 

 of the first rib, and is inserted into the under surface of the clavicle. 

 This muscle is concealed by the costo-coracoid membrane, an ex- 

 tension of the deep cervical fascia, by which it is invested. 



Relations. By its upper surface with the clavicle. By the lower 

 with the subclavian artery and vein, and brachial plexus, which 

 separate it from the first rib. In front with the pectoralis major, 

 the costo-coracoid membrane being interposed. 



Actions. The pectoralis major draws the arm against the thorax, 

 while its upper fibres assist the upper part of the trapezius in raising 

 the shoulder, as in supporting weights. The lower fibres depress 

 the shoulder with the aid of the latissimus dorsi. Taking its fixed 

 point from the shoulder, the pectoralis major assists the pectoralis 

 minor, subclavius, and serratus magnus, in drawing up and expand- 

 ing the chest. The pectoralis minor, in addition to this action, 

 draws upon the coracoid process, and assists in rotating the scapula 

 upon the chest. The subclavius draws the clavicle downwards and 

 forwards, and thereby assists in steadying the shoulder. All the 

 muscles of this group are agents in forcjed respiration, but are unable 

 to act until the shoulders be fixed. 



Lateral thoracic Region. 

 Serratus magnus. 



The Serratus magnus (serratus, indented' like the edge of a saw,) 

 arises by fleshy serrations from the nine upper ribs excepting the 

 first, and extends backwards upon the side of the chest, to be inserted 

 into the whole length of the base of the scapula. It indigitates by 

 means of its five lower serrations with the obli'quus externus abdo- 

 minis. 



Relations. By its superficial surface with the pectoralis major 

 and minor, the subscapularis, and the axillary ' vessels and nerves. 

 By its deep surface with the ribs and intercostal muscles, to which 

 it is connected by an extremely loose cellular tissue. 



Actions. The serratus magnus is the great external inspiratory 

 muscle, raising the ribs when the shoulders are fixed, and thereby 

 increasing the cavity of the chest. Acting upon the scapula, it 

 draws the shoulder forwards, as we see to be the case in diseased 

 lungs, where the chest has become almost fixed from apprehension 

 of the expanding action of the respiratory muscles. 



Anterior scapular Region. 



Subscapularis. 



The Subscapularis muscle arises from the whole of the under 

 surface of the scapula excepting the superior angle, and terminates 

 by a broad and thick tendon, which is inserted into the lesser tube- 



