PECTORALIS MAJOR AND MINOR. 225 



Dissection. Make an incision along the line of the clavicle, from the 

 jppei part of the sternum to the acromion process ; a second along the 

 lower border of the great pectoral muscle, from the lower end of the ster- 

 num to the insertion of its tendon into the humerus, and connect the two 

 by a third, carried longitudinally along the middle of the sternum. The 

 integument and superficial fascia are to be dissected together from off the 

 fibres of the muscle, and always 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 

 ^xpose the pectoralis 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, 

 from the cartilages of all the true ribs, excepting the first and last, and 

 from the aponeurosis of the external oblique muscle of the abdomen. It 

 is inserted by a broad tendon into the anterior bicipital ridge of the hu- 

 merus. 



That portion of the muscle which arises from the clavicle is separated 

 from that connected with the sternum by a distinct cellular interspace ; 

 hence we speak of the clavicular portion and sternal portion of the pecto- 

 ralis 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 formation 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 inserted into the lower part of the bicipital ridge ; and those of the 

 lower portion, 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 inte- 

 gument. 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 axillary vessels and 

 glands. By its external border with the deltoid, from which it is separated 

 above by a cellular interspace lodging the cephalic vein and the descend- 

 ing 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 incision perpendi- 

 cularly 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 reflect 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 pro- 

 cess of the scapula by a broad tendon. 



Relations. By its anterior surface with the pectoralis major and supe- 

 rior 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 trian- 

 gular space bounded above by the costo-coracoid membrane, and inter- 



