Description: The ilio-psoas m. is the combination of the lateral, triangular iliacus (from the iliac fossa), and the medial, longer, thick and round psoas major (from the lateral aspects of the L1-L5 vertebrae). They descend together laterally behind the inguinal ligament into the thigh where they insert on the lesser trochanter of the femur. The circulation is via the deep circumflex iliac a., and the innervation from L2-L4 via the lumbar plexus and the femoral nerve.