The iliacus and psoas major muscles of the hip are so closely related in structure and function that they are often referred to as a single muscle, the iliopsoas. While each muscle has its own origin – the iliacus arises from the ilium and the psoas major arises from the lumbar vertebrae – both muscles merge at their midpoint to form a common insertion at the lesser trochanter of the femur.
Working together, the muscles of the iliopsoas are the most powerful flexors of the thigh at the hip joint....