Quadriceps means "four-headed." Since one of the heads lies under the others, the whole group could considered as a single muscle with three distinct parts and a common tendon, not unlike triceps (cf.). Here, their shared properties will be described before being treated singly.
The insertion of the whole quadriceps group is a tendon that sheaths the patella and attaches onto the front of the tibia below the tubercle. This is called the patellar tendon.
All the quadriceps muscles straighten the leg at the knee. They originate on the femur below the head, except for rectus femoris ("REC-tus FEM-or-iss"), which begins on the pelvis. Its attachment on the pelvis allows it to contribute to the bending of the leg at the hip as well.
Vastus medialis (VAST-us mee-dee-AL-iss) and vastus lateralis (lat-er-AL-iss) have an elongated teardrop shape. These appear to meet in front, with medialis dropping lower. Rectus femoris fills the almond-shaped space between them.
Regarding the distance between the great trochanter of the femur and the patella, rectus femoris comes about two thirds of the way down, vastus lateralis about three-quarters, and medialis all the way to the kneecap.
The patellar tendon forms an important inverted-cone or wedge shape on the the very front of the knee below the patella.