PECTORAL MUSCLES 



103 



BREAST MUSCLES 



Pectoralis major. Origin. Clavicular portion, on the sternal 

 end of the calvicula; sterno-costal portion, on the surface of the 

 sternum and on six upper ribs. Insertion. By a broad strong 

 tendon on the shaft of the humerus, on the crest of the greater 

 tubercle (Figs. 79, 85). 



18 19 1R 



10 11 



FIG. 85. MUSCLES OF ANTERIOR ASPECT OF THORAX. 



1-5, Pectoralis major; 6, 9, pectoralis minor; 7, subclavius; 8, deltoid; 10, anterior 

 portion of anterior serratus; u, external oblique; 12, 13, latissimus dorsi; 14, teres 

 major. (Sappey.) 



Action. It draws the arm to the front of the thorax, opposing 

 the latissimus dorsi; thus it also is a " rowing" muscle. 



Thepectoralis minor is -entirely covered by the major. 



Origin. From three upper riba^the second, third, and fourth. In- 

 sertion. Th^coracoid process of the scapula. Action. It pulls the shoulder 

 downward. It may pull ribs upward in labored breathing or forced inspira- 



Nerves of both muscles. Anterior thoracic. 



Note. When the whole body is drawn upward by the hands, 

 as when hanging from a trapeze, the two pectorals, the trapezius 

 and the latissimus are acting together. 



The subclavius is a small muscle lying in the subclavian groove between 

 the clavicula and first rib. It may elevate the ribs or depress the clavicula. 



