AXILLARY SPACE 17 



Clean the pectoralis minor muscle without injuring the medial anterior 

 thoracic nerve which pierces it. 



M. Pectoralis Minor. The pectoralis minor is a triangular 

 muscle which rises from the anterior ends of the third, 

 fourth, and fifth ribs close to their junctions with their 

 cartilages and from the fascia covering the intercostal 

 muscles in the intervening spaces. Its fibres pass upwards 

 and laterally, and its tendon of insertion is attached to the upper 

 surface and the anterior border of the coracoid process near 

 its lateral extremity. When the muscle is in action it draws 

 the scapula downwards and forwards and depresses the 

 shoulder. It is supplied by the medial anterior thoracic 

 nerve. The greater portion of the pectoralis minor is concealed 

 by the pectoralis major, but the medial part of its inferior border 

 appears on the lateral wall of the thorax below the pectoralis 

 major ; its insertion is concealed by the anterior fibres of the 

 deltoid. 



Dissection. Clear away the clavipectoral fascia below the level of the 

 pectoralis minor and open up the lower part of the axilla, remove also the 

 deep fascia of the arm in the region of the lateral boundary of the axilla. 



Commence at the lateral part of the area below the pectoralis minor and 

 clean the coraco-brachialis and the short head of the biceps as they descend 

 into the arm from the tip of the coracoid process. Find the lower part of 

 the axillary artery at the medial border of the coraco-brachialis. The 

 trunk of the median nerve lies between the artery and the muscle, and at 

 the lower border of the pectoralis minor the medial head of the nerve 

 crosses the front of the artery. Pull the coraco-brachialis laterally and find 

 the musculo-cutaneous nerve entering its deep surface, just below the 

 pectoralis minor. Above and to the lateral side of the trunk of the musculo- 

 cutaneous nerve find the branch from it which supplies the coraco-brachialis. 

 The axillary vein lies along the medial side of the artery, and in the angle 

 between the artery and vein, anteriorly, is the medial cutaneous nerve 

 of the forearm (internal cutaneous). Running along the medial side of 

 the vein is the medial cutaneous nerve of the arm (lesser internal cutaneous 

 nerve) ; secure this and follow it upwards to the communication which it 

 receives from the intercosto-brachial nerve. At the same time identify and 

 preserve the lateral group of axillary lymph glands which lie along the 

 medial side of the axillary vein. Secure the intercosto-brachial nerve and 

 follow it medially, to the point where it emerges from the second intercostal 

 space, and laterally to the medial and posterior aspect of the arm where 

 it is distributed. 



In order to display the distribution of the intercosto-brachial nerve, and 

 to give better access to the medial and posterior walls of the axilla, the 

 axillary fascia must be separated from the fascia of the arm. When this 

 has been done the dissector should turn to the medial wall of the axilla and 

 find the anterior and posterior divisions of the lateral branches of the 

 intercostal nerves, as they emerge between the digitations of the serratus 

 anterior behind the inferior border of the pectoralis minor. These he 

 must trace forwards and backwards respectively, and he may expect to find 

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