Sciatic nerve. The sciatic nerve is the largest nerve of the body and carries contributions from L4 to S3 (Figs. 5.60 and 5.61). It: forms on the anterior surface of the piriformis muscle and leaves the pelvic cavity through the greater sciatic foramen inferior to the piriformis; passes through the gluteal region into the thigh, where it divides into its two major branches, the common fibular nerve (common peroneal nerve) and the tibial nerve—dorsal divisions of L4, L5, S1, and S2 are carried in the common fibular part of the nerve and the ventral divisions of L4, L5, S1, S2, and S3 are carried in the tibial part; innervates muscles in the posterior compartment of the thigh and muscles in the leg and foot; and carries sensory fibers from the skin of the foot and lateral leg.