Origin: Illiac crest to the last cervical vertebra.
Insertion: All thoracic ribs.
Action: Extension of the vertebral column. Raising of the cranial portion of the body from the pelvis, sacrum, and loin; in conjunction with the other muscles, fixation of the vertebral column; deflection of the back by fixation of the cervicothoracic junction; sudden raising of the caudal portion of the body; which is initiated by means of the rear extremities.
Nerve: Dorsal branches of the thoracic nerve.