Fig. 5. Cranial view of the femur and caudal views of the femur and TBT of an adult emu, showing the mean principal strain orientations on the different bone surfaces and the corresponding direction of torsional loading. In the femur (A), the principal tension (black arrows) measured at the bone's mid-shaft is oriented at 37° and 49° relative to the long axis of the bone on the cranial and caudal surfaces, respectively. The principal compression (reverse black arrows) is oriented at 90° to the principal tension. The orientation of the strains in the femur indicate torsional loading of the bone, acting to rotate the proximal end medially about the long axis relative to the distal end (as viewed from the cranial surface, grey arrows). (B) In the TBT (shown with adjacent fibula), the principal compression is oriented at 25° relative to the long axis, indicating a significant torsional component acting to rotate the proximal end medially relative to the distal end (as viewed from the caudal surface, grey arrows). The lengths of the black arrows representing the principal strains are not scaled to the strain magnitudes measured on these bone surfaces.