. Bulletin of the British Museum (Natural History) Zoology. CRANIAL ANATOMY AND PHYLOGENY OF BELODONTICHTHYS 151. rmx rme Fig. 19 Belodontichthys dinema: deeper cranial musculature. Muscle Al is cut through; the lower border of DO is indicated by dashed line crossing LAP (LILI 89008). large DO with a frontal origin occurs in the Diplomystidae. The presumed plesiomorphic condition of the DO (that which is regularly encountered in other ostariophysans) is present in Ictalurus where the muscle is small and vertically orientated, with its origin confined to the posteroventral region of the sphenot
. Bulletin of the British Museum (Natural History) Zoology. CRANIAL ANATOMY AND PHYLOGENY OF BELODONTICHTHYS 151. rmx rme Fig. 19 Belodontichthys dinema: deeper cranial musculature. Muscle Al is cut through; the lower border of DO is indicated by dashed line crossing LAP (LILI 89008). large DO with a frontal origin occurs in the Diplomystidae. The presumed plesiomorphic condition of the DO (that which is regularly encountered in other ostariophysans) is present in Ictalurus where the muscle is small and vertically orientated, with its origin confined to the posteroventral region of the sphenotic. The adductor arcus palatini (AAP) has a variable morpho- logy in the Siluridae. The usual condition is for the muscle to run between the parasphenoid and the pterygoid bones, while posteriorly it covers the lower part of the medial face of the hyomandibular and is considered a separate element, viz the adductor hyomandibularis (Winterbottom, 1974). This condition occurs in Belodontichthys, Hemisilurus, Silurus, Wallago, Silurichthys, Hito, Ompok, Kryptopterus bicirrhis, K. cryptopterus, K. limpok and K. moorei. In contrast, in K. bleekeri and K. apogon, the AAP extends dorsally to cover the orbitosphenoid, pterosphenoid and medial part of the ; frontal. Only in Schilbeidae (Schilbe) where the AAP attaches to the frontal (Fig. 26) have we encountered a condition similar to that in the two cited Kryptopterus species. In the other members of the Siluridae examined the epaxial musculature extends forward onto the frontal in Silurus, Wallago, Ompok and Hemisilurus. However, only in Wallago and Ompok does the musculature cover a large posterior area j of the bone. In Silurus only a small region of the bone is covered and the anterior border of the muscle is marked by a strong i transverse frontal ridge. Hemisilurus lacks the frontal concavity of the former taxa, the frontal being convex with the epaxial muscle inserting, as in Silurus, along a prominent frontal ridge. Like Belodo
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