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). 



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; n, 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. 



The pectoralis minor is entirely covered by the major. 



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

 sertion. The coracoid process of the scapula. Action. It pulls the shoulder 

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

 tion. 



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. 



