AXILLARY ARTERY. 377 



Course. This artery occasionally passes back between the sixth and seventh 

 cervical vertebrae, and sometimes between the first and second dorsal, or even below 

 the second. It has been seen to pass between the first rib and the transverse process 

 which supports it. 



AXILLARY ARTERY. 



The axillary artery, that part of the artery of the upper limb which 

 intervenes between the subclavian aiid the brachial portions, extends from 

 the outer border of the first rib to the lower margin of the tendons of the 

 latissimus dorsi and teres major muscles. In this course it passes through 

 the axilla, and its direction varies with the position of the limb, being 

 curved downwards or upwards, or being straight, according as the arm 

 hangs by the side, or is elevated, or extended. 



In front, the axillary artery is covered by the pectoralis major muscle, 

 behind which it is crossed by the pectoralis minor. It may be conveniently 

 divided into three parts : the first part lying internal to the pectoralia 

 minor muscle, and resting on the thoracic wall; the second part behind 

 that muscle, and passing from the thorax towards the shoulder ; the third 

 part beyond the muscle, and resting on the humerus. 



In the first part of its course the vessel is in contact with the serratus 

 magnus muscle on its inner side, and is covered by the costo-coracoid mem- 

 brane, which, attached above to the clavicle, is continued below into a 

 common sheath investing the artery and vein, and completed behind by a 

 prolongation of the deep cervical fascia. In this part of its course the 

 artery is placed with the trunks of the brachial plexus above and behind it, 

 and the axillary vein in front of it and somewhat nearer the thorax : it is 

 also crossed by the cephalic and acromio-thoracic veins as they dip down to 

 terminate in the axillary vein. 



In the second part of its course, behind the pectoralis minor, the axillary 

 artery is completely surrounded by the trunks of the brachial plexus, and 

 it is crossed in front by one of the roots of the median nerve : the vein is on 

 the thoracic side of the artery, separated from it by nerves. 



In the third part of its course, beyond the pectoralis minor, the axillary 

 artery rests on the subscapular muscle and the insertions of the latissimus 

 dorsi and teres major, while to the outer side is the coraco-brachialis muscle. 

 The axillary vein is still on the thoracic side, but sometimes the venae 

 comites, by whose union it is formed, are continued up to this level, one on 

 each side of the artery. The main branches resulting from the division of 

 the brachial plexus of nerves are disposed behind and on each side of this 

 part of the artery, as follows, viz., behind it, the circumflex and musculo- 

 spiral ; to its inner side, the ulnar and the two internal cutaneous ; to the 

 outer side, the external cutaneous and median. The external cutaneous 

 and the circumflex nerves leave the artery in the axilla, and at the lower 

 part of the axilla the median nerve is often before the vessel; in an opera- 

 tion, that nerve might serve as a guide to the position of the artery, for it 

 could be distinguished from the other large nerves (ulnar and musculo- 

 spiral) by the circumstance of its being the nearest to the pectoral muscle. 

 Beyond the border of the pectoralis major, the artery is covered only by 

 the skin and fascia on the inner side ; and here the flow of blood may be 

 controlled by pressure of the finger directed outwards against the humerus. 



BRANCHES. The branches of the axillary artery consist of the external 

 thoracic branches furnished to the muscles of the chest, the subscapular 



