THE AXILLARY ARTERY. 435 



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

 nearly opposite that from the outer side of the axillary artery. It passes outwards, 

 beneath the inner head of the biceps and the coraco-brachialis muscle, and resting 

 on the fore part of the humerus, until it reaches the bicipital groove. There it 

 divides into two branches, of which one ascends in the groove with the long head of 

 the biceps to the head of the bone and the capsule of the joint, while the other con- 

 tinues outwards, and anastomoses with the posterior circumflex branch. 



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

 "Tiving 1 off a much larger branch than usual, an arrangement which has been observed in the 

 proportion of one out of every ten cases. In one set of cases this large branch is continued 

 as one of the arteries of the forearm, most frequently the radial (about 1 in 33), sometimes 

 the ulnar (1 in 72), less frequently a vas aberrans, and very rarely the interosseous artery. In 

 another set of cases the large branch gives origin to the subscapular, the two circumflex, and 

 the two profunda arteries of the arm ; 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 stem of the branches instead of the 

 main vessel. This disposition may be explained by supposing that the stem of the branches 

 was originally the brachial artery, but that in early life it had become obstructed in its distal 

 part, 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 (p. 440). The proximal portion 

 of this aberrant vessel is represented normally by the muscular branch passing through the 

 loop of the median nerve. 



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

 anatomists have described that as the normal arrangement, giving the common trunk the 

 name of thoracic axis. The long thoracic artery often arises from the acromio-thoracic, or is 

 replaced by enlargement of the normal branches of that artery, and not unf requently is given 

 off by the subscapular. 



The subscapular artery is often united at its origin with the posterior circumflex : on 

 the other hand, the dorsal scapular branch 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 teres major muscle. 

 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, the anterior 

 circumflex and superior profunda together, or some other rarer combination of those vessels. 

 The posterior circumflex is sometimes double ; and so is the anterior, but more seldom. . 



An accessory external 'mammary branch is not unfrequently present, arising from the 

 axillary beyond the circumflex arteries, and running downwards and inwards to the side of 

 the chest behind the long thoracic. The following branches, usually derived from the sub- 

 clavian artery, have been seen in rare cases to arise from the axillary, viz., internal mammary, 

 suprascapular, and posterior scapular ; as have also the superior profunda, inferior profunda. 

 and anastomotic arteries, normally branches of the brachial. 



The third part of the axillary artery is frequently crossed by a muscular slip (axillary 

 arch) passing from the latissimus dorsi to the anterior wall of the axilla (p. 205). 



SURGICAL ANATOMY OF THE AXILLARY ARTERY. 



The artery is usually tied in the third part of its course, as it lies upon the tendon of the 

 latissimus dorsi. The limb having been carried away from the chest, an incision is made 

 parallel to and a little behind the anterior fold of the axilla. On cutting through the deep 

 fascia the vein is exposed, and by drawing this downwards the artery is brought into view, 

 surrounded by the nerves from the brachial plexus. The ligature is to be passed from within 

 outwards. Another and simpler mode of operating is that recommended by Malgaigne, 

 according to which the incision is made along the inner border of the coraco-brachialis 

 muscle, and the median nerve then serves as a guide to the artery, while the vein is not 

 exposed. In the rest of its course the artery is so deeply placed, and in such close relation 

 with the vein and nerves, that an operation on the third part of the subclavian is both easier 

 and more successful. 



Collateral circulation. After ligature of the third part of the axillary artery, the circula- 

 tion in the upper limb is carried on by means of the anastomoses of the posterior circumflex 

 and superior profunda arteries, and of smaller branches of the axillary and brachial arteries 

 in the coraco-brachialis, biceps, and triceps muscles. 



VOL. II. F P 



