四头肌肌肉组织由四个完全不同rent regions, each with a different origin. The rectus femoris originates on the anterior inferior iliac spine (AIIS). The vastus lateralis originates from the greater trochanter of the femur. The vastus medialis originates from the intertrochanteric line. The vastus intermedius originates from the shaft of the femur. Together, the muscles of the quadriceps work to extend the leg by straightening the knee.

The biceps femoris is located posterior to the femur, and is a part of the hamstring muscle group. The primary action of the biceps femoris is flexion of the leg by bending the knee.

The sartorius originates from the anterior superior iliac spine (ASIS) and inserts near the tibial tuberocity, running laterally to medially along the anterior thigh. Because the sartorius crosses both the hip and the knee, contraction of the muscle is capable of flexing both the leg and thigh. By running laterally to medially, shortening of the muscle also causes lateral rotation and abduction of the thigh.

Plantar flexion involves increasing the angle between the foot and the leg (pointing the toe). The gastrocnemius is found on the posterior portion of the leg, and is contracted in order to cause plantar flexion of the foot. The other muscle to contribute to this action is the soleus, also located in the posterior portion of the leg.

The tibialis anterior is located in the anterior portion of the leg and is involved in dorsiflexion, the opposite of plantar flexion. The biceps femoris and rectus femoris are located in the thigh, and do not act on the position of the foot. The biceps femoris is involved in flexion of the knee and the rectus femoris is involved in extension of the knee.

The quadriceps muscle group is primarily responsible for the extension of the knee. This group includes the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. The biceps femoris part of the hamstring muscle group and is responsible for the flexion of the knee.

The flexor digitorum brevis is sandwiched between the plantar aponeurosis and the tendons of the flexor digitorum longus. It flexes the lateral four digits at the proximal interphalangeal joints.

The gluteus maximus is innervated by the inferior gluteal nerve. The gluteus medius and minimus are innervated by the superior gluteal nerve. The femoral nerve does not innervate the glutes, and the obturator nerve innervates muscles in the medial thigh.

The short head of the biceps femoris is the only muscle of the posterior thigh that is not part of the "hamstring" muscle group. It is not cosnidered a hamstring muscle because it only crosses the knee joint; it does not act on the hip joint.

Only the short head of the biceps femoris is innervatd by the common fibular division of the sciatic nerve. The long head of the biceps femoris, the semimembranous, and the semitendinous are innervated by the tibial division of the sciatic nerve. The gluteus maximus is innervated by the inferior gluteal nerve.

All of the incorrect answer options are muscles of the anterior compartment of the leg. Muscles of the anterior compartment are involved in dorsiflexion of the ankle and are all innervated by the deep fibular nerve.

The fibularis longus is a muscle of the lateral comaprtment of the leg. Muscles of the lateral compartment of the leg are innervated by the superficial fibular nerve.

The piriformis passes through the greater sciatic notch and, in some people, is pierced by the sciatic nerve.