The iliacus is a flat, triangular muscle located in the pelvis. It originates from the iliac fossa, which is the inner surface of the ilium, a part of the hip bone. The iliacus muscle plays a crucial role in hip flexion, helping to lift the thigh towards the body. This muscle works closely with the psoas major, another muscle involved in hip flexion, to form the iliopsoas group. Together, they are essential for movements such as walking, running, and climbing. Proper function of the iliacus is important for maintaining stability and mobility in the lower body.