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l[=a]-tis'i-mus, n. the broadest muscle which lies upon the back.

Origin: Spines of 6 or 7 lower thoracic vertebrae, through lumbar fascia the spines of the lumbar and sacral vertebrae, crest of the ilium (outer lip), 3 or 4 lower ribs, often lower angle of scapula. Insertion: Bicipital groove of humerus. Nerve: Subscapularis longus. Action: Adducts, extends, and rotates arm inward.