Figure 17. Ventral rostrum of Psephurusand representatives of three genera of Acipenseridae: The rostrum is thin and tapers in Psephu-
rus(a) andHuso(b) with the groove for the rostral nerves (grn) opening laterally alongside the endochondral rostrum (large arrow in a,
b). Acipenserines (c, d) possess lateral ethmoid ridges (ler, open arrows) that bracket the groove to the tip of the rostrum (Character 27).
They are expanded as the lateral ethmoid shelves of scaphirhynchines (les; Character 39). Foramina for the nerves that innervate the
dorsal ampullary organs (nfand arrows) indicate expansion of the lateral ethmoid shelves. The parasphenoid (pas) is exposed as it
contacts the ventral rostral bones inHusoand polyodontids (a, b), but is coveredbythe central trabecular process in acipenserines (ctpin
c, d; Character 31).tr= trabecular ridge,vrb= ventral rostral bones.
martin jones
(Martin Jones)
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