526 THE ARTERIES 



to the bone, is sometimes difficult to secure in the operation for excision of the 

 shoulder-joint. 



Chief variations. — (a) The anterior circumflex may be given off from the jiu^terior circum- 

 flex ; or {b) I'rom a stem common to it and several other vessels. (See Variations in the 

 Axillary Artery, page 521.) 



3. The posterior circumflex artery (fig. 348) arises from the hinder part of 

 the axillary, just lielow thi- lower Itorder of the subscapularis muscle. It passes 

 through the quadrilateral space, bounded by the teres minor above, the latissimus 

 dorsi and teres major below, the humerus externally, and the long head of the 

 triceps internally, and, Avinding round the back of the humerus beneath the deltoid. 

 l)reaks up under cover of that muscle into a leash of branches, which for the most 

 part enter its substance. The circumflex nerve and two vena^ comites run with it. 

 It anastomoses with the anterior circumflex, the arteries on the acromion, and the 

 suj^erior profunda artery. 



In addition to the leash of vessels to the deltoid, it gives off the following small 

 branches: — (a) nutrient, to the greater tuberosity of the humerus; (6) articular, 

 to the back of the shoulder-joint; (c) acromial, to the plexus on the acromion; and 

 ((/) muscular, to the teres minor and long and short heads of the triceps. One or 

 more of these branches to the triceps (the tricipital) descend either between the 

 outer and long head, or in the substance of that muscle to anastomose with an 

 ascending branch from the superior profunda artery. It is by means of this 

 anastomosis that the collateral circulation is chiefly carried on when the axillary 

 or the brachial artery is tied between the origins of the posterior circumflex and 

 superior profunda arteries (fig 330). 



The chief variations in the posterior circumflex are: — {a) It may arise with the subscapular 

 artery as a cunimou trunk. (6) It may come ofi" from the brachial, and run up behind tlie teres 

 major to the quadrilateral space, (c) It may give off the inferior jirofunda, the anterior circum- 

 flex, or the dorsal scapular, {d) It may be double, (e) It may form one of the vessels arising 

 from a trunk common to several branches of the axillary and brachial arteries. (See VARIATIONS 

 in the Axillary Artery, page 521. 



THE BRACHIAL ARTERY 



The brachial artery, the continuation of the axillary, extends from the lower 

 border of the teres major \o a little below the centre of the crease at the bend of 

 the elbow, where it divides, opp(^site the junction of the head with the neck of 

 the radius, into the radial and ulnar arteries. The artery is situated at first inter- 

 nal to the humerus; but as it passes down the arm it gradually gets in front of tlie 

 bone, and at the bend of the elbow lies midway between the two condyles (fig. 

 350). Hence, in controlling haemorrhage, the artery should be comj)resse(l out- 

 wards against the bone in its upper third, outwards and backwards in its middle 

 third, and directly backwards in its lower third. Throughout the greater part of 

 its course the artery is superficial, being merely overlapped slightly on its outer side 

 by the coraco-brachialis and bice]>s muscles; but at the bend of the elbow it sinks 

 deeply beneath the semilunar fascia of the biceps into the triangular interval 

 (antecubital s])ace), bounded on either side by the supinator longus and })ronator 

 radii teres, and at its bifurcation is more or less under cover of these muscles (fig. 

 351). The sheath of the brachial artery is closely incorp(n"ated with the fascia 

 covering the l)ice])s muscle, and it is for this reason that in the operation for liga- 

 turing, the vessel is a])t to be retracted with the muscle. A line drawn from midway 

 between the folds of the axilla at the outer side of that space to midway between 

 the condyles of the humerus, will indicate its course. It is accompanied by two 

 veins which frequently communicate across the artery. 



