<P> The sensory and motor innervation to the lower limb is supplied by the lumbosacral plexus, which is formed by the ventral rami of the lumbar and sacral spinal nerves with additional contributions from the subcostal nerve (T12) and coccygeal nerve (Co1). Based on distribution and topography, the lumbosacral plexus is subdivided into the lumbar plexus (T12 - L4) and the Sacral plexus (L5 - S4); the latter is often further subdivided into the sciatic and pudendal plexuses: </P> <P> The lumbar plexus is formed lateral to the intervertebral foramina by the ventral rami of the first four lumbar spinal nerves (L1 - L4), which all pass through psoas major . The larger branches of the plexus exit the muscle to pass sharply downward to reach the abdominal wall and the thigh (under the inguinal ligament); with the exception of the obturator nerve which pass through the lesser pelvis to reach the medial part of the thigh through the obturator foramen . The nerves of the lumbar plexus pass in front of the hip joint and mainly support the anterior part of the thigh . </P> <P> The iliohypogastric (T12 - L1) and ilioinguinal nerves (L1) emerge from the psoas major near the muscle's origin, from where they run laterally downward to pass anteriorly above the iliac crest between the transversus abdominis and abdominal internal oblique, and then run above the inguinal ligament . Both nerves give off muscular branches to both these muscles . Iliohypogastric supplies sensory branches to the skin of the lateral hip region, and its terminal branch finally pierces the aponeurosis of the abdominal external oblique above the inguinal ring to supply sensory branches to the skin there . Ilioinguinalis exits through the inguinal ring and supplies sensory branches to the skin above the pubic symphysis and the lateral portion of the scrotum . </P> <P> The genitofemoral nerve (L1, L2) leaves psoas major below the two former nerves, immediately divides into two branches that descends along the muscle's anterior side . The sensory femoral branch supplies the skin below the inguinal ligament, while the mixed genital branch supplies the skin and muscles around the sex organ . The lateral femoral cutaneous nerve (L2, L3) leaves psoas major laterally below the previous nerve, runs obliquely and laterally downward above the iliacus, exits the pelvic area near the iliac spine, and supplies the skin of the anterior thigh . </P>

Anatomy of the back of the lower leg