Out of a total of 116 cadaver feet, 29 specimens were selected by means of palpation of the tuberosity of navicular fur a possible presence of the accessory navicular. They were then radiographed and the accessory navicular was detected in ten. Also three fresh amputation specimens with an accessory navicular were added to the study. A total of 13 legs was dissected and in nine of them, the tibialis posterior tendon inserted directly into the accessory navicular without extending to the sole of the foot. In these feet, the second part of the tibialis posterior tendon originated from the accessory navicular, extending to the normal insertions. There was no connection between these two parts and when traction was applied to either one, no movement was observed in the other. Also a fibrocartilaginous mass was detected in four specimens, probably formed to resist the friction between the tendon and the bone. These results may explain the pronated foot in the presence of the navicular, due to the lass of the function of the tibialis posterior tendon.