The latissimus dorsi muscle is one of the largest muscles in the back. There muscle is divided into two segments, which are configured symmetrically along the backbone. The muscle is located in the middle of the back, and it is partially covered by the trapezius. It originates along the seventh thoracic vertebra (T7) region of the spine and extends to its insertion point on the humerus. The muscle also covers the lower tip of the scapula, or shoulder blade. When flexed, the muscle works at extending, adducting and rotating the arm. Because of its size and central location, injury to this muscle can be debilitating. Injuries may include rips and tears. Once aggravated, the latissimus dorsi muscle is often the source of chronic shoulder and neck pain, and it can cause tendonitis of the shoulder joint. The thoracordorsal nerve serves this muscle. This nerve branches from the brachial plexus' posterior cord and follows the route of the subscapular artery.