The quadriceps femoris is the strong extensor muscle which lies on the anterolateral aspect of thigh. It is made up of four smaller muscles; they are the rectus femoris, the vastus lateralis, the vastus medialis, and the vastus intermedius, forming a large dense mass covering the front and sides of the femur.
Each of the heads of these muscles arises independently, but as they reach the knee-joint the form one tendon. This means that the individual tendons of these four muscles that constitute the quadriceps fuse into a common tendon at the distal part of the thigh and inserts into the patella and the tibial tuberosity.
The rectus femoris occupies the anterior surface of thigh, arising from the anterior inferior iliac spine by a fine tendon. The vastus lateralis lies on the anterolateral aspect of thigh, originating from the greater trochanter and the lateral lip of linea aspera of femur. The vastus medialis is located on the anteromedial side of thigh, taking origin also from the lateral lip of linea aspera of femur. The vastus intermedius lies on the anterior side of thigh, beneath the rectus femoris muscle, arising from the anterior surface of femur.
Action
Contraction of all the heads of the quadriceps femoris muscle extends the leg at the knee-joint, while the rectus femoris alone flexes the hip-joint. All of them contract when we rise up from a sitting position, and when we run and do sit-ups in the gym.
Innervation
This group of four muscles is innervated by the femoral nerve (from L2, L3 and L4).
Blood Supply
The quadriceps femoris is supplied by the lateral circumflex femoral and the profunda femoris artery.
Below, a diagrammatic picture of right thigh, showing three of the four muscles that make up the quadriceps group. The vastus medialis cannot be seen because it lies underneath the rectus femoris muscle.
