Fig. 9. Mid-shaft cross-sectional area (A) and the second moments of area across the x and y axes (I_xx and I_yy, respectively) for the emu (A) femur and (B) TBT versus body mass on logarithmic axes. Femur and TBT mid-shaft cross-sections from an adult bird (>8 years old, 37 kg) demonstrate the anatomical position of the axes about which the second moments of area were typically distributed, where I_xx (closed circles) and I_yy (open circles) are distributed about the x–x and y–y axes, respectively. (A) A: y=32x^0.59±0.06 (R²=0.87); I_xx: y=120x^1.38±0.07 (R²=0.95); I_yy: y=143x^1.43±0.08 (R²=0.90). (B), A: y=26x^0.63±0.05 (R²=0.95); I_xx: y=74x^1.37±0.08 (R²=0.93); I_yy: y=76x^1.45±0.07 (R²=0.92). The scaling patterns for the polar moments of area, J, were omitted for clarity as, being the sum of I_xx and I_yy, they nearly overlie the trends for I and scaled very similarly, J_FEMUR: y=264x^1.410±0.075 (R²=0.93) and J_TBT: y=150x^1.41±0.07 (R²=0.93).