Sciatic n.

The largest nerve in the body, the sciatic n. is formed from contributions from the L4, L5, S1, S2  and S3 spinal nerves.  It emerges from the greater sciatic foramen inferior to the pyriformis m. and descends into the posterior compartment of the thigh.  It provides motor innervation to the posterior compartment of the thigh, and the leg below the knee.