This section is from the book "Anatomy Of The Arteries Of The Human Body", by John Hatch Power. Also available from Amazon: Anatomy of the Arteries of the Human Body, with the Descriptive Anatomy of the Heart.
The Thoracica Alaris Artery is seldom found as a single trunk, its place being usually supplied by several smaller vessels : its origin is from the second stage of the axillary. It divides into many branches Which supply the areolar tissue and glands of the axilla.
In removing diseased glands from this cavity, the incautious division of the branches of this artery may be followed by smart hemorrhage, which will be difficult to control on account of the divided vessels retracting into the areolar tissue: to provide against this occurrence, Professor Colles advised a ligature to be passed round the vessel supplying the gland before it is divided.
The Thoracica Inferior, called also the thoracica longa or external mammary artery, arises opposite the lower margin of the pectoralis minor, or frequently whilst the artery is under cover of that muscle in its second stage; it then descends obliquely inwards, concealed by the lower edge of the pectoralis major: it supplies these muscles, and likewise the serratus anticus, intercostals, mammary gland and integuments, and anastomoses with the other thoracic arteries, the internal mammary, and the intercostal arteries.