lumbar plexus, a network of nerves formed by the ventral anterior primary divisions of the first three and the greater part of the fourth lumbar nerves. It is located on the inside of the posterior abdominal wall, either dorsal to the psoas major or among its fibers and ventral to the transverse processes of the lumbar vertebrae. The branches of the lumbar plexus are the iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, obturator, accessory obturator, and femoral nerves. The iliohypogastric, ilioinguinal, and genitofemoral nerves supply the caudal part of the abdominal wall. The lateral femoral cutaneous, obturator, accessory obturator, and femoral nerves supply the anterior thigh and the middle of the leg. Only 20% of people have the accessory obturator nerve, which comes from the third and the fourth lumbar nerves. Compare sacral plexus. See also lumbosacral plexus.
