External thoracic artery is a large vessel arising from the ventral face of the brachial artery at about the level of the anterior border of the first rib.
It passes backwards on the deep face of the deep pectoral muscle.
It gives off a number of branches to the pectoral muscles, axillary lymph gland, panniculus and skin.
One of its branches passes in the groove between the brachiocephalicus and anterior superficial pectoral muscle, supplies them and accompanies the cephalic vein.
This branch corresponds to the descending branch of the inferior cervical artery of the horse.