title: The cranial nerves of the Senegal bichir, Polypterus senegalus [osteichthyes: actinopterygii: cladistia].
abstract: The organization of the roots, ganglia and peripheral distribution of the rami of the cranial nerves of larval and juvenile Senegal bichirs was examined with a wide range of techniques, including gross dissection and histological preparations. The profundal nerve of bichirs is completely separate from the trigeminal nerve and innervates the skin overlying the orbit and snout, and there is no evidence that a superficial ophthalmic ramus of the trigeminal nerve exists. Bichirs appear to retain all six pairs of lateral line nerves that characterized the earliest gnathostomes, but the sensory ganglia of the anterodorsal and otic lateral line nerves have fused, and the sensory ganglia of the anterodorsal and anteroventral lateral line nerves are partially fused, which appears to be a shared derived character of ray-finned fishes. The anteroventral lateral line nerve of bichirs retains mandibular and opercular rami, a primitive feature shared with other bony fishes, and the fibers of the opercular ramus innervate all postotic ampullary organs. Surprizingly, bichirs, unlike most nonteleost bony fishes, have lost the spiracular organ. The lateral ramus of the posterior lateral line nerve of bichirs is divided into a pars dorsalis and a pars ventralis, which appears to be a shared derived character of bony fishes. The glossopharyngeal and vagal nerves of bichirs exhibit lateral and medial sensory ganglia, and this appears to be a shared derived character of bony fishes. The posttrematic rami of the glossopharyngeal nerve and both the pre- and posttrematic rami of the vagal nerve of bichirs are divided, which appears to be a shared derived feature of bony fishes. The hypobranchial nerve of bichirs is unusual in that it is formed by only two spinal nerves, a pattern also seen in gars, but not other bony fishes, and apparently a uniquely derived character.
authors.affiliation: Lehrstuhl für Spezielle Zoologie, Eberhard-Karls-Universität Tübingen, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Piotrowski
authors.forename: R G
authors.initials: RG
authors.lastname: Northcutt
mesh_terms: D000818:Animals; D005075:Biological Evolution; D003391:Cranial Nerves / Q000033:anatomy & histology* / Q000502:physiology*; D005724:Ganglia / Q000033:anatomy & histology*; D009833:Olfactory Pathways / Q000033:anatomy & histology*