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Arteries originating from the subclavian or axillary arteries and distributing to the anterior thoracic wall, mediastinal structures, diaphragm, pectoral muscles and mammary gland.

are three in number. They are distinguished into-1. The Internal Mammary, Arteria sternalis, A. Sous-sternal (Ch.), Internal thoracic. It arises from the subclavian, and descends obliquely inwards, from its origin to the cartilage of the third rib. Below the diaphragm it divides into two branches; the one external, the other internal. From its origin until its bifurcation, it gives branches to the muscles and glands of the neck, to the thymus, mediastinum, pericardium, and oesophagus. In each intercostal space it gives off internal and external musculo-cutaneous branches, and also, on each side, the superior diaphragmatic. Its two ultimate branches are distributed on the parietes of the abdomen, and anastomose with the external mammary, intercostal, lumbar, circumflexa ilii, and epigastric arteries. 2. The External Mammary Arteries are two in number, and are distinguished into superior and inferior. The superior external mammary, First of the thoracics (Ch.), Superior external thoracic, Superior thoracic, is furnished by the axillary artery. It descends obliquely forwards between the pectoralis major and pectoralis minor, to which it is distributed by a considerable number of branches. The inferior external mammary, the second of the thoracics (Ch.), Long or inferior thoracic, arises from the axillary artery, a little below the preceding. It descends vertically over the lateral part of the thorax; curves, afterwards, inwards; becomes subcutaneous and divides into a number of branches, which surround the breast. It gives branches to the pectoralis major, serratus major anticus, the intercostal muscles, the glands of the axilla, and the integuments of the breast.