Anatomy

Origin

Medial and lateral sacral crests, spinous processes and supraspinal ligament of lumbar and eleventh and twelfth thoracic vertebrae, and medial part of iliac crests

Insertion

Transverse processes of all thoracic vertebrae, between tubercles and angles of lower nine or ten ribs

Nerve

Dorsal primary divisions of spinal nerves

Actions

Extension, lateral flexion of vertebral column (in unilateral contraction), rotates ribs for forceful inspiration