Origin Spinous processes of inferior 6 thoracic vertebrae, thoracolumbar fascia, iliac crest, and inferior 3 or 4 ribs Insertion Floor of intertubercular groove of humerus Action Extends, adducts, and medially rotates humerus; raises body toward arms during climbing Innervation Thoracodorsal nerve (C6, C7, and C8) (C6, C7, C8) Arterial Supply Thoracodorsal artery