196 MYOLOGY. 



PECTORALIS MAGNUS. 



(Sterno-trochineus. ) 

 (PL. III. 19, 19. FIG. 75. //.) 



This muscle is situated on the infero- lateral part of the thorax, 

 and is large, irregularly four-sided, flat, and thick, the fibres 

 extending forwards and outwards. Slightly aponeurotic ante- 

 riorly, elsewhere it is fleshy. 



Origin. From the inferior border of the last three or four 

 bones of the sternum, the ensiform cartilage, and its fellow of 

 the opposite side ; externally from the cartilages of the false 

 ribs, fascia of the external oblique muscle of the abdomen, and 

 the abdominal tunic. 



Insertion. To the fascia on the inside of the arm, and to the 

 inner trochanter of the humerus, under the tendon of the coraco- 

 humeralis, and by fascia over the bicipital groove, to the external 

 trochanter. 



Relation. Externally with the panniculus, skin, and pectoralis 

 transversus ; internally with the fascia of the external oblique, 

 and the ribs ; anteriorly with the pectoralis parvus. 



Action. To draw the shoulder back and adduct the arm ; in 

 difficult respiration it acts as an inspiratory muscle. 



PECTORALIS ANXIOUS. 



(Sterno-humeralis. ) 



(Fie. 75. e.) 



Situated on the anterior part of the breast, it forms the fleshy 

 prominence seen in front. Short, thick, and fusiform, its fibres 

 extend outwards ; it is tendinous at its attachments, with a fleshy 

 belly. 



Origin. From the cariniforrn cartilage and first bone of the 

 sternum. It is directed somewhat backwards, outwards, and 

 downwards. 



Insertion. To a ridge on the anterior part of the shaft of the 

 humerus by fleshy fibres, and an aponeurotic tendon common also 

 to the levator humeri, and pectoralis transversus. 



Relation. Externally with the skin ; anteriorly with the 

 levator humeri and panniculus ; posteriorly with the pectoralis 

 magnus and transversus ; internally with the parvus. 



Action. Its chief action is to adduct the arm. 



