Figure 18. Probactrosaurus gobiensis Rozhdestvensky, 1966. PIN 2232/10. Sacral block in ventral view. This block appears to show a sacrum comprising 7 fused vertebrae. Closer inspection suggests that one of the vertebrae 'inv.ins' is not only inverted (the neural canal, nc, is shown ventrally), but it may well represent an additional (inserted) element judged by the comparative length of the adjacent ilia. Abbreviations: ac = acetabulum; ap = anterior process of the ilium; dv = dorsal vertebrae; inv.ins = an apparently inverted and inserted vertebral centrum; is.p = ischial peduncle; nc = neural canal; pu.p = pubic peduncle; s.1, s.6(7) = numbered sacrals; sy = partial sacricostal yoke.