psoas major /sō″əs/ [Gk, psoa, loin] , a long muscle originating from the transverse processes of the lumbar vertebrae and the fibrocartilages and sides of the vertebral bodies of the lower thoracic vertebrae and the lumbar vertebrae. It joins the iliacus to form the iliopsoas deep in the pelvis as it passes under the inguinal ligament and inserts in the lesser trochanter. It acts to flex and rotate the thigh and to flex and laterally bend the spine. Compare psoas minor.
