The psoas major (also psoas major muscle, latin: musculus psoas major) is a long muscle of the pelvis that joins with the iliacus and forms the iliopsoas.
The right and left psoas major muscles originate from the lateral sides of the first four lumbar vertebrae (L1 - L4) and intervertebral discs.
The psoas major inserts onto the lesser trochanter of the femur.
The major functions of the psoas major are flexion of the hip joint and external rotation of the thigh.
The psoas major is innervated by the muscular branches of the lumbar plexus.