The common peroneal nerve (common fibular nerve; external popliteal nerve; lateral popliteal nerve), about one-half the size of the tibial nerve, is derived from the dorsal branches of the fourth and fifth lumbar and the first and second sacral nerves.It descends obliquely along the lateral side of the popliteal fossa to the head of the fibula, close to the medial margin of the biceps femoris muscle. Where the common peroneal nerve winds round the head of the fibula, it is palpable.