This is a long, narrow muscle, stretching across the ribs a little distance from the spine.

Origin. - It is composed of two sets of tendons. By one set it arises from the transverse process of the first lumbar vertebra and the anterior borders of the ribs. By the other it is inserted into the posterior edges of the fourteen anterior ribs and into the transverse process of the last cervical vertebra.

Action. - To assist in expiration.