Muscle · Chest

Subcostal

Musculi subcostales

Thin muscular slips on the INSIDE of the chest wall, best developed low down near the angles of the lower ribs. They run in the same direction as the internal intercostals but ignore the rule those muscles follow: instead of filling one space, each slip crosses one or two, skipping a rib on its way from the inner surface of one to the inner surface of another below. Because they lie against the pleura, they are met from within rather than from the skin. They pull the ribs they hold toward each other, acting with the other deep layers of the chest wall in a forced breath out.