n :  any of the arteries supplying or lying in the intercostal spaces  a  :  any of the arteries branching in front directly from the internal thoracic artery to supply the first five or six intercostal spaces or from its branch comprising the musculophrenic artery to supply the lower intercostal spaces - called also anterior intercostal artery   b  :  any of the arteries that branch from the costocervical trunk of the subclavian artery to supply the first or first two intercostal spaces or of the nine or 10 arteries that branch from the aorta to supply the lower intercostal spaces - called also posterior intercostal artery  .
 
 
 
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