102 ANATOMY OF UTPER EXTREMITY, ETC. 



The dissection of these two muscles completed, the pectoralis major 

 may be divided through its middle and the two ends reflected ; in so 

 doing, some offsets of the thoracica acromialis and superior thoracic 

 arteries will be cut across, as well as the short thoracic nerve, given 

 off from the brachial plexus just below the clavicle. On clearing 

 away the fat and cellular tissue, the pectoralis minor muscle comes 

 into view. 



The PECTORALIS MINOR MUSCLE arises by three distinct 

 tongues from the third, fourth, and fifth ribs, and is in- 

 serted into the anterior border of the coracoid process of 

 the scapula, in common with the short head of the biceps 

 and coraco-brachialis muscles. 



Connected with the upper border of the pectoralis minor 

 and inserted into the first rib and the coracoid process, and 

 to the clavicle between these points, is a dense fascia called 

 the costo-coracoid membrane. When this is removed it 

 will be found to have concealed a small muscle called the 

 subclavius. 



The SUBCLAVIUS MUSCLE arises by a short thick tendon 

 from the cartilage of the first rib ; its fibres are directed 

 outward and are inserted into the under surface of the 

 clavicle for more than half its length; this muscle receives 

 a muscular nerve from the brachial plexus behind the 

 clavicle. 



AXILLA. 



The dissection pursued thus far will have exposed a 

 large space filled with fat, cellular tissue and lymphatic 

 glands, lying behind the pectoralis minor, and through 

 which pass the axillary artery, with its vein, and the bra- 

 chial plexus of nerves; this space is called the AXILLA. 

 The pectoralis minor forms but a small part of its anterior 

 boundary, which is completed by the pectoralis major; the 

 posterior boundary is formed by the flat tendon of the 

 latissimus dorsi, by the teres major and sub-scapularis 

 muscles; internally it is limited by the serratus magnus 

 and externally by the biceps and coraco-brachialis muscles. 



Keeping the arm well extended, patience and a little ingenuity in 

 hooking aside the branches of arteries and filaments of nerves, to 

 make room for the scalpel to reach others, will accomplish the display 

 of the axillary artery and its branches. The brachial plexus of nerves, 

 surrounding the artery, will, to a certain extent, be prepared in this 

 dissection. Veins which it is impossible to avoid dividing should be 

 tied, so that the blood oozing from them may neither soil nor obscure 

 the dissection. In a locality like this, the dissector will find the 

 scissors a most effective and serviceable instiument. 



