Raw PCSA (cm2) data scaled using individual group allometric exponents. (a) Shoulder rotators (M0.78) (b) shoulder adductors (M0.75), (c) shoulder abductors (M0.67), (d) shoulder flexors (M0.66), (e) shoulder extensors (M0.85), (f) elbow flexors (M0.50), (g) elbow extensors (M0.68), (h) supinators (M0.52), (i) pronators (M0.72), (j) wrist flexors (M0.73), (k) wrist extensors (M0.55), (l) digital flexors (M0.56), (m) digital extensors (M0.79). Chimpanzees are shaded in medium grey, bonobos in light grey, gorillas in dark grey and orangutans in white.