The<unk>  or kneecap is a thick, triangular bone which articulates with the femur and covers and protects the front of the knee joint. It is the largest sesamoid bone in the human body. It is attached to the tendon of the quadriceps femoris muscle, which contracts to straighten the leg. The vastus intermedialis muscle is attached to the base of<unk> . The vastus lateralis and vastus medialis are attached to lateral and medial borders of<unk>  respectively.
The<unk>  is stabilised by the insertion of vastus medialis and the prominence of the anterior femoral condyles, which prevent lateral dislocation during flexion. The retinacular fibres of the<unk>  also stabilise it during exercise.
The primary functional role of the<unk>  is knee extension. The<unk>  increases the leverage that the tendon can exert on the femur by increasing the angle at which it acts.
The<unk>  ossifies between the ages 2-6 years. In some people it may be absent congenitally or hypoplastic. In 2% of the population there is a bipartite<unk> , which is usually asymptomatic.
Regarding non-human animals, the<unk>  is fully developed only in placental mammals; marsupials have only rudimentary, non-ossified<unk> e.
Patella
Calcaneus
Dactylis
Humerus
Culmen 
Viscus
Ainhum
Condylox