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latissimus dorsi la·tis·si·mus dor·si (lā-tĭs'ə-məs dôr'sī)
A muscle with origin from the spinous processes of the lower thoracic and lumbar vertebrae, the median ridge of the sacrum, and the outer lip of the iliac crest, with insertion into the humerus, with nerve supply from the thoracodorsal nerve, and whose action adducts the arm, rotates it medially, and extends it.
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).