ANTERIOR THORACIC REGION. 



373 



the anterior surface of the sternal half of the clavicle ; from half the breadth 

 of the front of the sternum, as low down as the attachment of the cartilage of 

 the sixth or seventh rib; its origin consisting of aponeurotic fibres, which 

 intersect with those of the opposite muscle ; it also arises from the cartilages 



Fig. 236. Muscles of the Chest and Front of the Arm. Superficial View. 



of all the true ribs, with the exception, frequently, of the first, or of the seventh, 

 or both ; and from the aponeurosis of the External Oblique muscle of the abdo- 

 men. The fibres from this extensive origin converge towards its insertion, giv- 

 ing to the muscle a radiated appearance. Those fibres which arise from the 

 clavicle, pass obliquely outwards and downwards, and are usually separated 

 from the rest by a cellular interval : those from the lower part of the sternum 

 and the cartilages of the lower true ribs, pass upwards and outwards ; whilst 

 the middle fibres pass horizontally. As these three sets of fibres converge, 

 they are so disposed that the upper overlap the middle, and the middle the 

 lower portion, the fibres of the lower portion being folded backwards upon 

 themselves ; so that those fibres which are lowest in front, become highest at 



