226 ANTERIOR SCAPULAR REGION. 



nally by the ribs. In this space are found the axillary vessels and nerves,, 

 and in it the subclavian artery may be 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 extension 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 mem- 

 brane 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 expanding 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 forced respiration, but are in- 

 capable of acting until the shoulders are 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 upon its anterior aspect. In structure 

 the muscle is composed of three portions, a superior portion formed by 

 two serrations attached to the second rib, and inserted into the inner sur- 

 face of the superior angle of the scapula, a middle portion composed of 

 the serrations connected with the third and fourth ribs, and inserted into 

 the greater part of the posterior border, and an inferior portion consisting 

 of the last five serrations which indigitate with the obliquus externus and 

 form a thick muscular fasciculus which is inserted into the scapula near its 

 inferior angle. 



Relations. By its superficial surface with the pectoralis major and mi- 

 nor, the subscapularis, and the axillary vessels and nerves. By its deep 

 surface with the ribs and intercostal muscles, to which it is connected b^ 

 an extremely loose cellular tissue. 



Jlctions. The serratus magnus is the great external inspiratory muscle, 

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

 ravity of the chest. Acting upon the scapula, it draws the shoulder for- 

 wards, 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. 



interior Scapular Region. 

 Subscapularis. 



The SUBSCAPULARIS muscle arises from the whole of the under surface 

 of the scapula excepting the superior and inferior angle, and terminates by 



