The accessory bones are developmental anomalies and appear in the foot between the ages of 10 and 20 years. The most commonly occurring accessory bones are the os trigonum at the posterior plantar surface of the talus, the os tibiale externum (an accessory of the navicular bone), and the os intermetatarseum 1 through 2. These accessory bones as well as the sesamoids become sources of irritation and may require excision. Comprehensive accounts of the accessory bones of the foot can be found in the studies of Dwight, Kohler and Simmer, Marti, O’Rahilly, and Trolle.