246 The Axilla 



fossa (p. 241) ; and that the very end of the third part of the vessel is 

 comparatively superficial. He does not consider the relations of the 

 three parts separately, but regards the artery as a continuous trunk. 



In front are the skin, superficial fascia and platysma, the deep 

 fascia, and the pectoralis major and minor. Just below the clavicle 

 the vessel is covered by the costo-coracoid membrane, and is crossed 

 by the cephalic vein. The subclavius also overhangs the beginning 

 of the artery, but in operations at that part the clavicle is raised, so 

 that the muscle may be out of the way. The formation of the median 

 nerve takes place over the third part of the artery. 



Behind. As the axillary artery is the continuation of the sub- 

 clavian, which rests upon the first rib, its beginning must needs rest 

 upon the first intercostal space and the top of the serratus magnus. 

 The nerve of Bell descends behind the beginning of the artery to 

 reach the chest-wall. The artery there rests upon the subscapularis, 

 the posterior cord of the plexus and its derivatives the musculo- 

 spiral and circumflex and on the tendons of the latissimus dorsi and 

 teres major. And, as the shoulder-blade does not lie flat against the 

 ribs, the artery crosses a gap in its course from the intercostal space to 

 the subscapularis. 



To the inner side is the axillary vein in the whole of the course 

 of the artery, the inner cord of the plexus and its derivatives inter- 

 vening between the two vessels in the second and third parts of their 

 course. 



To the outer side are the brachial plexus and the derivatives of the 

 outer cord, namely, the musculo-cutaneous and the outer head of the 

 median. At the lowest part of the artery the last-named nerve is to 

 the outer side, as are also the coraco-brachialis and biceps. 



Branches. The first duty of the axillary artery is to give offbranches 

 to the side of the chest. The further that the artery descends, the 

 wider is the gap between it and the chest, and the longer are its 

 thoracic branches. The first is the short one. The second is the 

 inner division of the acromiaJ -thoracic ; the third is" the long one. ; the 

 fourth is the alar ; the fifth is the subscapular, which is very largely 

 concerned in the supply of the serratus magnus and chest-wall. All 

 these arteries anastomose with vessels which are already between the 

 ribs the superior intercostal of the subclavian in the back of the 

 highest spaces, and the aortic intercostals in the lower ; and the 

 anterior intercostals of the internal mammary in the front of each 

 space. 



The acromial division of the acromial-thoracic runs through the 

 costo-coracoid membrane, and anastomoses in the region from which 

 it takes its name with branches of the supra-scapular and circumflex 

 arteries. A descending branch runs in the inter-muscular groove with 

 the cephalic vein. The Jong thoracic descends by the lower border 

 of the pectoralis minor to the chest, giving branches through to the 



