The latissimus dorsi is a large, flat muscle on the back that stretches to the sides, behind the arm, and is partly covered by the trapezius on the back near the midline. ORIGIN: The latissimus dorsi originates via lumbodorsal fascia into spines of T7-L5, lower 4 ribs & iliac crest. INSERTION: The latissimus dorsi is inserted at the floor of the intertubercular groove of the humerus. ACTION: the agonist of arm extension. powerful arm adductor. medially rotates arm & shoulder. depresses scapula. pulls the body upward & forward with arms fixed overhead. NERVE SUPPLY: The latissimus dorsi is innervated by the sixth, seventh, and eighth cervical nerves through the thoracodorsal (long scapular) nerve.