The large bone between the femur and tarsometatarsus in the leg of a bird. It is formed by the union of the proximal part of the tarsus with the tibia.

in birds and some dinosaurs, the hind limb bone formed by the fusion of the bottom of the tibia, or calf bone, with the astragalus, the largest ankle bone of dinosaurs and birds. In most dinosaurs, the astragalus was firmly attached to the tibia but not fused with it