Abstract
1. Three hundred and thirty-three fresh and cleaned adult and foetal Japanese calcanei were observed for the forward extension complex of the posterior talar articular surface.
2. Three types of the forward extension complex were represented and one additional type is added for comparison.
3. The forward extension complex was in general markedly developed in the adult calcanei, whereas it was absent or incompletely developed in the foetal ones.
4. From the anatomical, topographical and mechanical points of view, the cause of the forward extension complex was to be sought in pressure and rubbing of both posterior talar articular surface and facies externa accessoria corporis tali during such eversion-abduction-dorsiflexion of the subtalar joint as secured the stability of the foot in the postnatal squatting posture.
