Biceps femoris muscle
As the name biceps implies, the biceps femoris has two heads, similar to the biceps brachii muscle in the arm. The two heads are the reason it has two main actions - the long head is solely responsible for extending the hip, while both act on the knee.
The biceps femoris is innervated by two branches of the sciatic nerve (L5, S1). The long head is innervated by the tibial nerve, a branch of the sciatic nerve, and the short head by the common peroneal nerve, also a branch of the sciatic nerve.