Rider's bones are ossification of
Rider's bone develops in the tendon of adductor longus in professional riders. It is a sesamoid bone.that has no periosteum and ossifies after bih. Reference: BD Chaurasia's handbook of general anatomy, 5th edition, pg 55
Adductor brevis
Adductor longus
Adductor magnus
Flexor digitorum superficialis
Upper limb