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one of several inconstant muscles of the posterolateral thoracic wall having the same direction as the internal intercostal muscles but extending across (that is, deep to) one or more ribs.
muscles that span multiple ribs, extending from the internal surfaces of one rib to the internal surface of the second or third rib below. They are more numerous in the lower regions of the posterior thoracic wall. They parallel the course of the internal intercostal muscles and extend from the angle of the ribs to more medial positions on the ribs below.