Neutron diffraction has been used to determine the preferred orientation of the hydroxyapatite crystals at the lower front edge of the tibia. The bones are compared for two Neolithic Orkney tribes. At Isbister, a muscular tribe on a hilly site engaged in heavy uphill work, whereas a tribe at Quanterness lived on level ground. The two sets are contrasted with the texture of present-day amputations. Values of 16, 8 and 3 are found for an `index of manoeuvrability' for the Isbister, Quanterness and modern ankles, respectively.