CIRCUMFLEX ARTERIES. BRACHIAL ARTERY. 381 



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 terminates by rami- 

 fying in the deltoid muscle and on the shoulder-joint, and by anastomosing 

 with the anterior circumflex and suprascapular arteries, as well as with the 

 acromial thoracic. 



The anterior circumflex, 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 

 park 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 anastomoses with the posterior circumflex 

 branch. 



PECULIARITIES. The most important peculiarity 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 proportion of one out of every ten cases. In one set of 

 cases, this large branch forms one of the arteries of the fore-arm ; most frequently 

 the radial (about 1 in 33), sometimes the ulnar (1 in 72), and, rarely, the interosseous 

 artery (1 in 506 : R. Quain). 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 trunk of the branches instead of the main vessel. This dis- 

 position may with probability be explained by supposing that the trunk of the branches 

 is the true brachial artery, but that in early life it has become obstructed below, and 

 that there has 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 normal arrangement, giving the com- 

 mon trunk the name of thoracic axis. The long thoracic artery often arises from the 

 acromial thoracic, or is replaced by enlargement of the normal branches of that 

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



The dorsalis scapulae 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, the anterior circum- 

 flex 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. 



BRACHIAL ARTERY. 



The brachial or humeral artery, the continuation of the axillary, extends 

 from the lower border of the posterior fold of the axilla, to about a finger's 

 breadth below the bend of the elbow, or to a point opposite the neck of the 

 radius, where it divides into the radial and ulnar arteries. The vessel 

 gradually inclines from the inner side to the fore part of the limb, lying in 

 the depression along the inner border of the coraco-brachialis and biceps 

 muscles ; and its direction may be marked out by a line drawn from 



