916 THE VASCULAK SYSTEM. 



the lateral and posterior cords of the brachial plexus and the lateral anterior thoracic 

 nerve. Below and to the medial side is the axillary vein, the medial anterior thoracic 

 nerve intervening. 



Relations of the Second Part Posterior. Behind the second part of the artery are 

 the posterior cord of the brachial plexus and a layer of fascia which separates it from the 

 subscapularis muscle. Anterior. In front is the pectoralis minor, and, more superficially, 

 the pectoralis major, the fasciae and skin. Lateral. To the lateral side lies the lateral cord 

 of the brachial plexus. Medial. On the medial side the medial cord of the plexus lies in 

 close relation to the artery, and intervenes between it and the axillary vein. 



Relations Of the Third Part Posterior. The third part of the artery rests 

 posteriorly upon the lower border of the subscapularis, the latissimus dorsi, and the 

 teres major. It is separated from the fibres of the subscapularis by the axillary (O.T. 

 circumflex) and radial (O.T. musculo-spiral) nerves, and from the latissimus dorsi and 

 teres major by the radial nerve alone. Anterior. It is crossed in front by the medial 

 head of the median nerve. In its upper half it lies under cover of the lower part of 

 the pectoralis major, the fasciae and skin, whilst its lower part, which is superficial, is 

 covered by skin and fasciae only. Lateral. To the lateral side lie the median and 

 musculo-cutaneous nerves and the coraco-brachialis muscle. Medial. To the medial side 

 is the axillary vein. The two vessels are, however, separated by two of the chief branches 

 of the medial cord of the brachial plexus, for in the angle between the vein and the artery, 

 and somewhat in front of the latter, lies the medial cutaneous nerve of the forearm 

 (O.T. internal cutaneous nerve) ; and, in the angle behind is the ulnar nerve. The medial 

 cutaneous nerve of the arm (O.T. lesser internal cutaneous) lies medial to the vein, and 

 the venae comites of the brachial artery ascend along the medial side, to terminate in 

 the axillary vein at the lower border of the subscapularis muscle. 



BRANCHES OF THE AXILLARY ARTERY. 



(1) Arteria Thoracalis Suprema. The highest thoracic artery is a small 

 branch which arises from the first part of the axillary at the lower border of 

 the subclavius. It runs downwards and medially, across the first intercostal 

 space, pierces the medial part of the costo-coracoid membrane, and supplies branches 

 to the subclavius, the pectoralis major and minor, and to the serratus anterior 

 (O.T. magnus) and the intercostal muscles; it anastomoses with branches of the 

 transverse scapular, the internal mammary, and the thoraco-acromial arteries. 



(2) Arteria Thoracoacromialis. The thoraco-acromial artery (Fig. 766) arises 

 near the upper border of the pectoralis minor, from the second part of the axillary 

 artery. It is a very short trunk, of considerable size, which passes forwards, 

 pierces the costo-coracoid membrane, and terminates, deep to the clavicular portion 

 of the pectoralis major, by dividing into four terminal branches clavicular, pectoral, 

 deltoid, and acromial. 



(a) The clavicular branch is a long slender artery which runs upwards and medially, 

 to the sterno-clavicular joint, anastomosing with the supreme thoracic, with branches of 

 the transverse scapular, and with the first perforating branch of the internal mammary 

 artery. It supplies the adjacent muscles and the sterno-clavicular articulation. 



(b) The pectoral is a large branch which descends between the two pectoral muscles, 

 to both of which it gives branches, and it anastomoses with the intercostal and lateral 

 thoracic arteries. 



(c) The deltoid branch runs distally, in the groove between the pectoralis major and 

 the deltoid, where it lies by the side of the cephalic vein, as far as the insertion of the 

 deltoid. It anastomoses with the acromial branch and with the anterior circumflex artery, 

 and it gives branches to the pectoralis major and deltoid muscles and to the skin. 



(d) The acromial branch runs upwards and laterally, across the tip of the coracoid 

 process, to the acromion ; it anastomoses with the deltoid branch, with the acromial 

 branches of the transverse scapular, and with the posterior circumflex arteries. It gives 

 branches to the deltoid. 



(3) Arteria Thoracalis Lateralis. The lateral thoracic artery arises from the 

 second part of the axillary, and descends, along the lower border of the pectoralii- 

 minor, to anastomose with the intercostal and subscapular arteries and with the 

 pectoral branch of the thoraco-acromial. It supplies the adjacent muscles, anc 

 sends mammary branches to the lateral part of the corresponding mammary gland 



