latissimus dorsi
muscle
latissimus dorsi, widest and most powerful muscle of the back. It is a large, flat, triangular muscle covering the lower back. It arises from the lower half of the vertebral column and iliac crest (hipbone) and tapers to a rounded tendon inserted at (attached to) the front of the upper part of the humerus (upper-arm bone). The action of the latissimus dorsi draws the upper arm downward and backward and rotates it inward, as exemplified...