Figure 15.Basitrabecular processes of representatives of all genera of Acipenseridae: Basitrabecular processes (btp) extend ventrally
beneath the orbit (top in cross-hatch). Morphology varies within Acipenser (b, c), but they are flattened shelves in Huso (a; (Character 25).
Scaphirhynchines (d, e) possess indepent basitrabecular cartilages (btc) bound to small basitrabecular processes (Character 43).
cartilage dominates the jaw joint in polyodontids
(Figure 16a, b) with its posterior end expanded as a
bulb displacing the palatoquadrate (also in Huso,
Figure 16c). Scaphirhynchines and all species of
Acipenserexamined possess jaw joints with approx-
imately equal contact among elements (Figure 16d,
e) or jaw joints with dominant palatoquadrate-in-
terhyal contact (i.e.A. oxyrinchus).