The _internal mammary_, or _internal thoracic artery_ (Fig. 73, No. 16) arises on the inner side of the sternum and extends downward and backward, giving nutrient branches to the anterior vena cava and to the diaphragm. At the point of the costo-sternal muscle it divides into an inner and an outer branch. The inner branch supplies the costo-sternal muscle and extends along the ribs and along their juncture with the breast-bone. It finally extends posteriorly, giving numerous branches to the abdominal muscles. The outer branch is distributed in a similar manner, giving off branches to the diaphragm and to the abdominal muscles, and anastomoses, on the surface of the abdominal muscles, with the epigastric artery. The _external thoracic artery_ (Fig. 73, No. 3), ramus superior, supplies principally the large breast muscles. The _inferior thoracic artery_, external ramus inferior, passes along the outside of the pectoralis major muscle, extends downward, and gives off the arteria thoracica longa (subcutaneous thoracic). This latter artery supplies the skin of the breast region. Other branches are given off to the muscles of the breast and to the skin of the region, and some finally anastomose with the branches of the sternal artery. 3. The =axillary artery= (Fig. 73, No. 12) extends out of the thoracic cavity along with the brachial nerve plexus. It gives off the _subscapularis_ which supplies the muscles of the scapular region. The axillary artery terminates as the _brachialis_ which passes between the biceps brachii and anconeus muscles downward along the humeral shaft. It gives off the anterior humeral circumflex artery and the brachialis profunda artery (Fig. 68, No. 3). It gives off near the elbow-joint the ulnar and radial arteries. The _anterior circumflex humeral artery_ passes through the short head of the biceps and gives off a branch to the biceps muscle, supplying the insertional part of the breast muscles. BRANCHES OF THE BRACHIALIS PROFUNDA The brachialis profunda artery (Fig. 68, No. 3) continues as the _posterior circumflex humeral artery_. This artery supplies the muscles of the posterior part of the humerus, the skin of the wing, and the muscles of the brachial region. The trunk of the arteria brachii profunda passes downward along the anconeus muscle, supplying that muscle and giving off the collateral ulnar artery. On the ulnar olecranon it anastomoses with the recurrent ulnar, thus establishing, at this region, collateral circulation. The rest of the brachialis sends branches to the biceps muscle and to the skin of the upper arm, and finally gives off the arteria collateralis radialis, which supplies the condylo-ulnaris. It then anastomoses with the end branches of the recurrent radialis artery.