Deep to the costal cartilage of the sixth rib, locate the internal thoracic artery [lungs are removed in another exercise] and identify its two terminal branches: the musculophrenic artery that runs laterally along the costal margin and the superior epigastric artery that runs more medially in an inferior direction. The musculophrenic artery gives anterior intercostal arteries in the 7-11th intercostal spaces and muscular branches to the costal border of the diaphragm. The superior epigastric artery pierces the diaphragm and enters the rectus sheath posterior to the rectus abdominis muscle. The further course of this artery will be studied when the abdominal wall is dissected ( see Laboratory Thirty-Five).
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