Figure 2. Anterior (upper panels) and lateral (lower panels) views of plots of ellipsoids of mean intercept lengths and Young’s moduli. The axes of the ellipsoids correspond to 3 principal directions. The distance from the surface to the center of the ellipsoid depicts the magnitude of mean intercept length or Young’s modulus. The three-dimensional orientation of the ellipsoids is emphasized by the meridians. Ellipsoids were constructed with the average H₁, H₂, and H₃, and the average E₁, E₂, and E₃ (n = 11; see Table for means and SD values). Differences in the magnitude of the mechanical ellipsoids are primarily related to differences in bone volume fractions (compare superolateral and inferomedial regions). Differences in the magnitudes of the principal directions are related to the amount of structural and mechanical anisotropy. Since the mechanical anisotropy (E₁/E₃) is larger than the structural anisotropy (H₁/H₃), the Young’s moduli ellipsoids are flatter than the mean intercept length ellipsoids.