transversus thoracis

noun

transversus tho·​ra·​cis -thə-ˈrā-səs 

: a thin flat sheet of muscle and tendon fibers of the anterior wall of the chest that arises especially from the xiphoid process and lower third of the sternum, inserts into the costal cartilages of the second to sixth ribs, and acts to draw the ribs downward

called also transverse thoracic muscle