26 THE UPPER EXTREMITY 



in the axilla, but it is rarely present as a separate branch, and its place 

 is usually taken by twigs from the subscapular and lateral thoracic 

 arteries. 



A. Subscapularis. The subscapular artery is the largest 

 branch of the axillary artery. It arises opposite the inferior 

 border of the subscapularis muscle and, following this, it runs 

 downwards and backwards, to the inferior angle of the 

 scapula, where its terminal twigs anastomose with the 

 descending branch of the transverse cervical artery. In the 

 lower part of its course it is accompanied by the thoracodorsal 

 nerve. Not far from its origin the subscapular artery 

 gives off a large branch, the A. rircumflexa scapula, which 

 winds round the axillary border of the scapula, in close 

 contact with the bone, to reach its dorsal aspect. Numerous 

 smaller twigs are given to the neighbouring muscles. 



Aa. Circumflexse Humeri (O.T. Anterior and Posterior 

 Circumflex Arteries). These are two in number, and as a 

 rule they both arise from the axillary at the same level, a short 

 distance distal to the origin of the subscapular artery. The 

 arteria circumflexa humeri posterior is much the larger of the 

 two. Only a small portion of it can be seen at the present 

 stage. It springs from the posterior aspect of the axillary, and 

 at once proceeds backwards, with the axillary nerve, close to 

 the medial and dorsal aspect of the head of the humerus, and 

 in the interval between the subscapularis and teres major 

 muscles. The small arteria circumflexa humeri anterior takes 

 origin from the lateral aspect of the axillary, and runs laterally, 

 in front of the surgical neck of the humerus, under cover of 

 the coraco-brachialis and short head of the biceps brachii. 

 Reaching the sulcus intertubercularis, it divides into two 

 branches. Of these one is directed proximally, along the long 

 head of the biceps brachii, to the shoulder-joint ; the other 

 passes laterally, to the under surface of the deltoid, and finally 

 anastomoses with some of the terminal twigs of the posterior 

 circumflex artery of the humerus. 



Vena Axillaris (The Axillary Vein). This vein has the 

 same extent as the artery. It begins at the lower border of 

 the teres major, as the upward continuation of the basilic vein 

 of the arm, and it becomes the subclavian vein at the lateral 

 margin of the first rib. At the lower margin of the subscapu- 

 laris it receives the two vencz comites of the brachial artery, 

 and above the level of the pectoralis minor it is joined by the 



