The latissimus dorsi muscle is a lower back muscle. However, the proximal end of the muscle wraps around the torso extending toward the anterior side. What structure of the homers does this muscle attach to? Solution Latissmus dorsi muscle is the large ,flat ,dorsolateral muscle on the trunk, posterior to the arm and partly covered by the trapezius on its mid dorsal region.It is the widest muscle of the body. It is responsible for the extension,adduction ,transverse extension , flexion from the extended position and internal rotation of the shoulder joint and it also has synergestic role in extension and lateral flexion of the lumbar spine. It attaches to the floor of the intertubercular sulcus between the two major muscles the pectoralis major and teres major..