Quadriceps Femoris Muscle

The quadriceps femoris (Latin for "four-headed [muscle] of the femur"), also called simply the quadriceps, quadriceps extensor, or quads, is a large muscle group that includes the four prevailing muscles on the front of the thigh. It is the great extensor muscle of the knee, forming a large fleshy mass which covers the front and sides of the femur. It is the strongest and leanest muscle in the human body.

It is subdivided into four separate portions or 'heads', which have received distinctive names:

* Rectus femoris occupies the middle of the thigh, covering most of the other three quadriceps muscles. It originates on the ilium. It is named from its straight course.

* The other three lie deep to rectus femoris and originate from the body of the femur, which they cover from the trochanters to the condyles:
o Vastus lateralis is on the lateral side of the femur (i.e. on the outer side of the thigh).
o Vastus medialis is on the medial side of the femur (i.e. on the inner part thigh).
o Vastus intermedius lies between vastus lateralis and vastus medialis on the front of the femur (i.e. on the top or front of the thigh).