520 THE ARTERIES 



THE AXILLARY ARTERY 



The term axillary is applied to that portiuu of the main arterial stem of the 

 upper limb that passes through the axilla. The axillary artery therefore is con- 

 tinuous with the subclavian above and with the brachial below. It extends from 

 the outer border of the lirst rib to the lower edge of the teres major nmscle, and has 

 the shoulder-joint and the neck of the humerus to its outer side. "\Mien the arm 

 is placed close to the side of the body, the artery forms a gentle curve with its 

 convexity upwards; but when the arm is carried out from the side at right angles 

 to the trunk in the ordinary dissecting position, the vessel takes a nearly straight 

 course, which will then be indicated by a line drawn from the middle of the 

 clavicle to a spot midway between the condyles of the humerus. The axillary 

 artery is at first deeply placed beneath the pectoral muscles, but in its lower third 

 is superficial, being covered onl}^ by the skin and the superficial fascia and deep 

 fascia. It is divided into three parts — first, second, and third, according as it lies 

 respectively above, beneath, or below the pectoralis minor. 



The Pirst Part of the Axillary Artery 



The first part of the axillary artery extends from the outer border of the first 

 rib to the upper border of the pectoralis minor. It measures about an inch in 

 length (2 '5 cm.). 



Relations. — In front it is covered by the skin, superficial fascia, the origin of 

 the platysma, the deep fascia, the pectoralis major, the costo-coracoid membrane, 

 the subclavius muscle and the clavicle when the arm hangs down by the side. The 

 cephalic and acromio-thoracic veins, the external anterior thoracic nerve, and the 

 axillary lymphatic trunk, cross over it. A layer of the deep cervical fascia which 

 has ])assed under the clavicle also descends in front of it. 



Behind, it rests upon the first intercostal space and first intercostal mus- 

 cle, the first digitation and sometimes a portion of the second digitation of 

 the serratus magnus muscle, and a part of the second rib. The posterior or 

 external respiratory nerve of Bell, on its way to the serratus magnus muscle, 

 passes behind it. 



To its outer side, and somewhat on a higher plane, are the cords of the 

 brachial plexus. 



To its inner side, and on a slightly anterior plane, is the axillary vein. The 

 anterior internal thoracic nerve courses between the vein and the arterv. 



The Second Part of the Axillary Artery 



The second part of the axillary artery (fig. 346) lies lieneath the pectoralis 

 minor deep in the axilla. It measures a little more than an inch in length 

 (3 cm.). 



Relations. — In front, in addition to the pectoralis minor, it is covered by the 

 pectoralis major and tlie integuments. 



Behind, it is separated by a considera1)le interval containing loose connective 

 tissue and fat from the subscapularis muscle; whilst behind, and in contact with 

 it, is the posterior cord of the brachial plexus. 



To the inner side, but separated from the arterv by the inner cord of the 

 brachial plexus, is the axillary vein. 



To the outer side is the outer cord of the l)rachial })lexus, and at some little 

 distance the coracoid process. 



It is thus seen that the second portion of the axillary artery is surrounded on 

 three sides by the cords of the brachial plexus — one behind, one internal, and one 

 external. 



