398 THE AXILLARY ARTERY. 



turning closely round the border of the scapula, which is frequently 

 grooved to receive it, passes between the teres minor and the bone, and 

 ramifies in the infraspinous fossa, where it anastomoses with the supra- 

 scapular and posterior scapular arteries. 



Branches. — The dorsalis scapulas gives off, — (i?) ventral branches, slender 

 vessels which ramify in the subscapular fossa between the subscapular muscle 

 and the bone, and anastomose with twigs from the suprascapular and posterior 

 scapular arteries ; {h) branches to the teres muscles, and particularly a twig which 

 ■descends between their origins ; (r) teiTainal branches in the infraspinous fossa. 



6. The posterior circumflex artery, a considerable vessel but 

 smaller than the subscapular, arises opposite the lower border of the 

 subscapular muscle, below the subscapular artery, and is directed back- 

 wards in company with the circumflex nerve, passing through the 

 space between the teres muscles, the humerus, and the long head of the 

 triceps muscle, and therefore separated by the long head of the triceps 

 from the subscapular artery. It winds round the humerus, and ter- 

 minates by ramifying in the deltoid muscle and on the shoulder- joint, 

 and by anastomosing with the anterior circumflex and suprascapular 

 arteries, as well as with the acromio-thoracic. 



7. The anterior circumflex artery, much smaller than the posterior 

 circumflex, arises nearly opposite to it or lower down, and from the outer 

 side of the axillary artery. It passes from within outwards and forwards, 

 under the inner head of the biceps and the coraco-brachialis muscle, 

 resting on the fore part of the humerus, until it reaches the bicipital 

 groove. There it divides into two branches, one of which ascends in 

 the groove with the long head of the biceps, to the head of the bone 

 and the capsule of the joint ; the other continues outwards, and anas 

 tomoses with the posterior circumflex branch. 



Varieties. — The most important variety in the trunk of the axillary artery 

 consists in its giving off a much larger branch than usual, — an arrangement which ■ 

 has been observed in the pi'oportion of one out of every ten cases. In one set of 

 cases, this large branch is continued as one of the arteries of the fore-arm ; most 

 frequently the radial (about one in 33), sometimes the ulnar (1 in 72), and. 

 rarely, the interosseous artery (1 in 606 : R. Quain). In another set of cases, the 

 large branch gives origin to the subscapular, the two circumflex, and the two 

 profim.da ai-teries of the aim ; but sometimes only one of the circumflex, or only 

 one of the deep humeral arteries, arises from it. In the second class of cases the 

 divisions of the brachial plexus of nerves surround the common trunk of the 

 branches instead of the main vessel. This disposition may with probability be 

 explained by supposing that the trunk of the branches was originally the brachial 

 arteiy, but that in early life it had become obstructed below, and that there had 

 become developed in its place, as an apparent brachial artery for the supply of 

 the lower portions of the limb, a vas aberrans, such as is sometimes seen arising 

 from the brachial artery, and uniting with one of its branches. 



The superior thoracic artery is so frequently given off by the acromio-thoracic, 

 that some anatomists have described that as the nonnal arrangement, giving the 

 common trunk the name of thoracic axis. The long thoracic artery often rises 

 from the acromio-thoracic. or is replaced by enlargement of the normal branches 

 of that artery, and not unfrequently is given off by the subscapular. 



The dorsalis scapulte sometimes springs directly from the axillary artery. 



The posterior circumflex artery is sometimes removed from the axillary to the 

 superior profunda branch of the brachial, in which case it ascends behind the 

 tendons of the latissimus dorsi and teres major. In another class of cases not 

 quite so numerous, the posterior circumflex gives off one or more branches usually 

 derived from other sources : as for example (placing them in the order of 

 frequency), the anterior circumflex, the superior profunda, the dorsal scapular, 



