The iliopsoas is the great flexor muscle of the hip joint. The term iliopsoas refers to the combination of the psoas major and the iliacus at their inferior ends. These muscles are distinct in the abdomen, but usually indistinguishable in the thigh. As such, they are usually given the common name "iliopsoas" and are referred to as the "dorsal hip muscles" or "inner hip muscles". The psoas minor does not contribute to the iliopsoas muscle. The psoas major originates along the lateral surfaces of the vertebral bodies of T12 and L1-L5 and their associated intervertebral discs. The iliacus originates in the iliac fossa of the pelvis. The psoas major unites with the iliacus at the level of the inguinal ligament and crosses the hip joint to insert on the lesser trochanter of the femur. The psoas major is innervated by direct branches off the lumbar plexus at the levels of L1 and L2, while the iliacus is innervated by the femoral nerve (which is composed of nerves from the anterior rami of L2-L4).