Figure 1.

Iliac trabecular architecture in Homo sapiens (SCR 252) (a) and Hylobates syndactylus (AIZIU 1726) (b) (not to scale). ab, anterior; sb, superior; pb, posterior; pcb, pericotyloid; icb, iliocotyloid; spb, sacropubic bundle; and iib, ilioischial bundle; rt, radial trabeculae; tc, trabecular crossing between the spbs and the iibs. Major gait-related features in the trabecular system of human ilium (a) include: a distinctive iib, a strong, undivided spb, and a diagonal full crossing (tc) of these bundles over the acetabulum. In H. syndactylus (b), as well as in all extant apes, a true iib is absent because of the lack of trabecular structural organization, resulting in a honeycomb-like cancellous network. The poorly structured inner bundles do not form a full crossing, but only partially flow into a slightly higher-density confluence of trabeculae located well high above the acetabular upper rim.