Fig. 1

A sagittal plane shadow drawing of C-T section 23, midway through the metatarsal specimen, defining its intersesamoidal ridge (crista), is illustrated in Figure a. Its distal cartilaginous surface, highlighted in teal, has been described as a convex spherical surface ([7, 4, 8, 9, 6, 10]). Figure b is a shadow drawing of the same metatarsal specimen from a dorsal perspective, highlighting its circular form in the transverse plane. A black dotted semi- circle (first described by Stokes and colleagues [11]), with its center of rotation designated CR, has been superimposed over the distal metatarsal edge in the sagittal and transverse planes to illustrate its distal spherical surface. The length of radius in figure 1b is slightly longer than 1a, which results in its distal surface being more flattened in the transverse plane than the sagittal plane figure in 1a. Although both images exhibit two geometrically different convex circular surfaces, it is possible to integrate both CR into one functional model