Explanation:
The latissimus dorsi, a large flat muscle on the back, originates from the lower six thoracic vertebrae, lumbar vertebrae, lower three to four ribs, and the iliac crest. It inserts at the bicipital groove of the humerus and is involved in several actions including the adduction, extension, and medial rotation of the shoulder. This muscle is key in movements that involve pulling or lifting, contributing to the dynamic motion involved in activities like swimming, rowing, and climbing.