Quadriceps – 3 big muscles (vastus) and the rectis femoris (means 4 big heads) – all extend the knee 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. - only quad that crosses the knee. Also is the only quad that flexes the hip , but it not very good at this compared to ileopsoas muscles.
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:
- Vastus lateralis is on the lateral side of the femur (i.e. on the outer side of the
Vastus medialis is on the medial side of the femur (i.e. on the inner part thigh).
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), but deep to the rectus femoris. Typically, it cannot be seen without dissection of the rectus femoris.