The differences are most easily described by discussing the resulting change in the site of origin of the thoracic artery.
The thoracic artery arises from the subclavian opposite the base of the coracoid artery, or from the base of the coracoid artery.
The medial migration of the thoracic artery appears to have some phylogenetic significance as yet not understood.
The thoracic artery usually passes ventral to M. costi-sternalis anterior.
From the ventral trunk of the thoracic artery a variable number of small vessels arises to supply the costosternal articulations.
Occasionally a small artery could be traced from the main trunk of the thoracic artery to that muscle.
In doves the thoracic artery arose consistently from the pectoral stem, lateral to the origin of the axillary artery.
Minor variations in all of the smaller branches of the thoracic artery were common.
Where the trunk passes under M. sternocoracoideus, the thoracic artery is given off.
The thoracic artery , arising from the pectoral stem, characteristically bifurcates at the anterior end of M. costi-sternalis.
thoracic artery n.
The internal mammary artery, with origin in the subclavian artery and bifurcations to the musculophrenic and superior epigastric arteries; internal thoracic artery.
The external mammary artery, with origin in the axillary artery and distribution to the muscles of the chest and mammary gland; lateral thoracic artery.
An artery with origin in the axillary artery, with distribution to the muscles of the chest, and with anastomoses to the branches of the suprascapular, internal thoracic, and thoracoacromial arteries; superior thoracic artery.