The lattissimus dorsi muscle (sometimes translated as the "broadest muscle of the back") is a flat triangular muscle caudal to scapula.
Origin: Begins as a wide, tendinous leaf from the superficial leaf of the lumbosacral fascia and thus from the spinous processes of the lumbar vertebrae and the last seven or eight thoracic vertebrae, and it arises muscularly from the last two or three ribs.
Insertion: Teres tubercle and the greater tubercle of the humerus.
Action: To draw the limb forward and possibly laterally; depression of the vertebral column; support the limb, draw the limb against the trunk, draw the free limb backward during flexion of the shoulder joint. Decelerates forward motion of the limb.
Nerve: Pectorales caudales and thoracodorsalis.