Posterior Compartment of the Thigh

Question 1

What muscles are the extensors of the thigh and flexors of the leg?

Answer 1

• Semitendinosus
• Semimembranosus
• Biceps femoris

Question 2

What are the muscles which extend the thigh and flex the leg innervated by? What is the exception?

Answer 2

• All tibial division of sciatic nerve (L5, S1, S2)
• EXCEPT the short head of biceps femoris - common fibular division of sciatic nerve
• Note : Thigh extensors and leg flexors = semitendinosus, semimembranosus and biceps femoris

Question 3

Why is the short head of the biceps femoris not regarded as a true hamstring muscle?

Answer 3

• Short head attaches to femur itself (whereas other hamstring muscles attach to the ischial tuberosity)
• This different attachment point means that the short head does not cross the hip joint so cannot extend the thigh
• Short head is innervated by the common fibular division of the sciatic nerve (whereas the other hamstring muscles are innervated by the tibial division)