The structure indicated is the rectus femoris of the quadriceps group of thigh muscles.
The rectus femoris is one of the muscles that makes up the quadriceps femoris, and is contained in the anterior compartment of the thigh. The muscles of the anterior compartment are all innervated by the femoral nerve and serve generally to extend the leg at the knee joint.
The four muscles that make up the quadriceps femoris are the:
- Rectus femoris
- Vastus lateralis
- Vastus medialis
- Vastus intermedius
In addition to the quadriceps muscles, the Sartorius muscle is also located in the anterior compartment together with the distal ends of the iliopsoas muscles. The rectus femoris has two heads:
- Reflected head
- Straight head
The reflected head attaches above the acetabulum, whereas the straight head attaches to the anterior inferior iliac spine. It is important to note that the points of origin for the rectus femoris muscle mean that the muscle traverses the hip joint, unlike the other muscles of the quadriceps: this means that the rectus femoris additionally has action at the hip joint and is a weak flexor of the hip.
Origin: Straight head – from anterior inferior iliac spine. Reflected head – groove just above acetabulum.
Insertion: Base of patella (then joins patella ligament to attach to tibial tuberosity)
Action: Flexion of the thigh at the hip joint. Extension of the leg at knee joint.
Innervation: Femoral nerve
Learn more about the anatomy of the thigh muscles in this tutorial.