The lumbar plexus is a nerve plexus (a network of intersecting nerves) in the body's lumbar region. It is formed by the ventral branches of the first to the fourth upper lumbar nerves (L1-L4), with the last thoracic nerve (or T12) usually supplementing the first lumbar level by a small branch.
The loops of communication between the first three lumbar levels and the greater portion of the fourth lumbar nerve form the lumbar plexus. The first lumbar nerve, or L1, divides into an upper and lower branch. The upper and bigger branch splits into the ilioingual and iliohypogastric nerves. The lower branch unites with the second lumbar nerve (L2), which – along with L3 and L4 – splits into ventral and dorsal divisions.
The lumbar plexus is embedded in the muscle psoas major, passing in front of the hip joint. It works with the sacral plexus to give autonomic, motor, and sensory fibers to the lower extremities and to the body's gluteal and inguinal (groin) regions.