PECTORALIS MAJOR AND MINOR. 203 



I 



in the direction of their course. For this purpose the dissector, if 

 he have the right arm, will commence with the lower angle of the 

 flap ; if the left, with the upper angle. He will thus expose the pec- 

 toralis major muscle in its whole extent. 



The Pectoralis major muscle arises from the sternal two-thirds of 

 the clavicle, from one half the breadth of the sternum its whole length, 

 and from the cartilages of all the true ribs, excepting the first. It 

 Js inserted by a broad tendon into the anterior bicipital ridge of the 

 humerus. 



That portion of the muscle which arises from the clavicle, is sepa- 

 rated from that connected with the sternum by a distinct cellular 

 interspace ; hence we speak of the clavicular portion and sternal por- 

 tion of the pectoralis major. The fibres from this very extensive 

 origin converge towards a narrow insertion, giving the muscle a 

 radiated appearance. But there is a peculiarity about the forma- 

 tion of its tendon which must be carefully noted. The whole of the 

 lower border is folded inwards upon the upper portion, so that the 

 tendon is doubled upon itself. Another peculiarity results from this 

 arrangement: the fibres of the upper portion of the muscle are in- 

 serted into the lower part of the ridge ; and those of the lower por- 

 tion, into the upper part. . 



Relations. By its external surface with the fibres of origin of the 

 platysma myoides, the mammary gland, the superficial fascia and 

 integument. By its internal surface, on the thorax, with the clavicle, 

 the sternum, the costal cartilages, intercostal muscles, subclavius, 

 pectoralis minor, and serratus magnus ; in the axilla, with the axil- 

 lary vessels and glands. By its external border with the deltoid, 

 from which it is separated by a cellular interspace lodging the 

 cephalic vein and the descending branch of the thoracico-acromialis 

 artery. Its lower border forms the anterior boundary of the axillary 

 space. 



The pectoralis major is now to be removed by dividing its fibres 

 along the lower border of the clavicle, and then carrying the inci- 

 sion perpendicularly downwards, parallel to the sternum, and at 

 about three inches from its border. Divide some loose cellular 

 tissue, and several small branches of the thoracic arteries, and re- 

 flect the muscle outwards. We thus bring into view a region of 

 considerable interest, in the middle of which is situated the pectoralis 

 minor. 



The Pectoralis minor arises by three digitations from the third, 

 fourth, and fifth ribs, and is inserted into the anterior border of the 

 coracoid process of the scapula by a broad tendon. 



Relations. By its anterior surface with the pectoralis major and 

 superior thoracic vessels and nerves. By its posterior surface with 

 the ribs, the intercostal muscles, serratus magnus, axillary space, 

 and axillary vessels and nerves. Its upper border forms the lower 

 boundary of a triangular space bounded above by the costo-coracoid 

 membrane, and internally by the ribs. In this space are found the 



