AXILLARY 521 



The Third Part of the Axillary Artery 



The third part of the axillary artery (tig. 346) extends from the lower l)order 

 of the pectoralis minor to the lower border of the teres major. Its upper half lies 

 deeply placed within the axilla, beneath the lower edge of the pectoralis major 

 muscle, l)ut its lower half is in the arm external to the axilla, and is uncovered by 

 muscle. It measures about three inches in length (7 '5 cm.). 



Relations. — In front it has, in addition to the skin and superficial fascia, the 

 I)ectoralis major above, and lower down the deep fascia of the arm. It is crossed 

 obliquely b}^ the inner root of the median nerve and Ijy the outer brachial vena 

 comes. 



Behind, it lies successively ujion the subscapularis, the latissimus dorsi, and 

 tores major muscles. From the first-named muscle it is separated at first by a con- 

 siderable mass of fat and cellular tissue. The musculo-spiral and circumfiex 

 nerves intervene V^etween the arter}^ and the muscles. 



On its outer side it is separated from the bone by the coraco-brachialis, by 

 which it is jjartly overlapped, this muscle and the short head of the biceps serving 

 as a guide to the artery in ligature. For a part of its course it has also the musculo- 

 cutaneous nerve and the outer root of the median nerve to its outer side. 



To its inner side it has the axillary vein, the ulnar nerve, the internal cutaneous 

 nerve, the lesser internal cutaneous nerve, and the inner root of the median nerve. 

 The ulnar nerve is between the artery and the vein. The internal cutaneous nerve 

 is a little in front of the artery as well as internal to it. 



]^ariations in the Axillary Artery 



The chief variations in the axillary artery are : — (a) It may give off the radial artery; 

 [h) more rarely, the ulnar artery ; (c) still mure rarely, the interosseous arteiy, or a vas aberrans ; 

 [d) it may give off a common trunk, from which may arise the sub.scapulai', the anterior and 

 posterior circumflex, and the superior and inferior profunda arteries. The branches of tlie 

 brachial plexus usually surround this common tiTink, and not what is apparently the main brachial 

 artery. The latter vessel indeed would seem in many of these instances to be reallj' an enlarged 

 vas aberrans, and the common trunk the main brachial artery, the lower portion of which has 

 been obliterated, i.e. obliterated from the last branch given off from the common trunk to the 

 si)Ot where it is again joined by the vas aberrans. {e) The axillarj' artery may be covered in 

 the third part of its course by a muscular sli]) (the dorsi axillaris), derived from the ujjper i»art 

 of the tendon of the latissimus dorsi, and alwaj^s present in early foetal life, though as a rule 

 atrophied later. 



Branches of the Axillary Artery 



The first part gives off: — (1) The superior thoracic; and (2) the acromio- 

 thoracic. 



The second part gives oft': — (1) The long thoracic; and (2) the alar thoracic. 



The third part gives off: — (1) The subscajtular; (2) the anterior circumfiex; 

 and (8) the posterior circumflex. 



Branches of the First Part of the Axillary Artery 



1. The superior or short thoracic is variously given oft" from tlit- axiUary 

 artery, usually either as a conniion trunk with the next l)ranch, the acromial 

 thoracic, or a little above. It passes behind the axillary vein across the first inter- 

 costal space, supplying the intercostal muscles and the upper ])ortion of the ser- 

 ratus magnus, and anastomoses with the intercostal arteries. At times it sends a 

 branch between the pectoralis major and minor, which then, as a rule, more or 

 less takes the place of the pectoral branch of the acromial thoracic. 



2. The acromio-thoracic, or thoracic axis, arises from the front part of the 

 axillary just above the U])per border of the pectoralis minor. It is a short trunk, 

 and coming off from the front of the artery pierces the costo-coracoid membrane, 

 and then divides into three or four small l>ranches, named from their direction: — 

 {<!) the acromial, or thoracica acromialis; (//) the humeral, or thoracica humeralis; 

 (c) the pectoral, or short thoracic of some autliors; and (c/) the clavicular. 



