Summary Psoas Origin Anterior surfaces and lower borders of transverse processes of L1 - L5 and bodies and discs of T12 - L5 Insertion Lesser trochanter Action Flex the torso and thigh with respect to each other Innervation Direct fibers of L1 - L3 of lumbar plexus (L1, L2, L3) Arterial Supply Lumbar branch of iliopsoas branch of internal iliac artery