34 THE SUPERIOR EXTREMITY 



this vessel and the posterior circumflex. In the former case, 

 the circulation is carried on by the anastomosis between the 

 intercostals, lateral thoracic, descending branch of transverse 

 cervical, transverse scapular (supra-scapular), and thoraco- 

 acromial arteries, on the proximal side of the ligature, and the 

 subscapular and humeral circumflex arteries, on the distal side 

 of the ligature. 



Collateral Circulation. The circumflex arteries anastomose with 

 the acromial branch of the thoraco-acromial and the transverse scapular 

 (p. 1 8). The subscapular anastomoses with the descending branch of the 

 transverse cervical and the transverse scapular arteries in the scapular 

 anastomosis, and with the intercostals, the lateral thoracic and pectoral 

 branches of the thoraco-acromial in the serratus anterior, near the inferior 

 angle of the scapula. 



When the axillary artery is tied between the subscapular and circumflex 

 vessels, the anastomosis just referred to between the circumflex, the acromial 

 branch of the thoraco-acromial and the transverse scapular arteries re- 

 establishes the circulation. 



When the subscapular and circumflex vessels arise by a common trunk 

 and a ligature is applied distal to this vessel, the collateral anastomosis follows 

 the same course as in ligature of the brachial artery proximal to the origin 

 of the (superior) profunda (p. 43). 



Branches of the Third Part of the Axillary Artery. (i) The 

 subscapular is the largest branch of the axillary artery. It arises near the 

 lower border of the subscapularis, along which it descends accompanied 

 by its companion vein and the thoraco-dorsal (long subscapular) nerve. 

 A short distance from its origin it gives off the circumflex scapular (dorsalis 

 scapulce) artery, which winds round the axillary border of the scapula close, 

 to the bone to reach its dorsal surface (p. 33). (2) The posterior circumflex 

 (p. 18). (3) The anterior circumflex (p. 18). 



These three arteries occasionally arise by a common trunk, which leaves 

 the third part of the axillary artery near its commencement. 



Aneurism of the first part of the axillary artery pushes forwards the costo- 

 coracoid membrane and tends to project below the clavicle in the superficial 

 infra-clavicular triangle. Aneurism of the third part projects into the axilla 

 and gives rise to a swelling or convexity of the floor of the axilla. Both 

 varieties may press upon the axillary vein and obstruct the venous return, 

 thus causing swelling and redema of the upper limb. 



The Axillary Vein is formed at the lower border of the 

 teres major by the basilic vein, and is soon joined by the venae 

 comites of the brachial artery. It ends at the outer border 

 of the first rib, where it becomes continuous with the subclavian 

 vein. As it passes through the axilla it lies to the medial side 

 of the artery, but is separated from it by the ulnar nerve, below, 

 and by the medial cord of the plexus, above. When the arm is 

 abducted, the vein lies in front of the artery and hides it from 

 view. Its principal tributaries are the cephalic and the 

 subscapular veins. The latter possesses a wide anastomosis 

 with the veins of the thoracic wall near the inferior angle of 



