no hyoidean hemibranch, and that the pseudobranch is really a persistent spiracular pseudobranch;[293] hence it is probable that a like significance must be attached to this singular structure in other Teleosts. The evidence of the cranial nerves on this point is conflicting. If the pseudobranch pertains to the spiracular cleft its nerve supply should be derived from the nerve of that cleft—viz. the seventh or facial nerve; but if it represents a hyoidean hemibranch, then one would expect it to be innervated by the ninth or glossopharyngeal nerve. As a matter of fact, however, the organ is said to be supplied by the seventh in some Teleosts, and in others by the ninth nerve. In the Dipnoi the branchial system is best developed in _Neoceratodus_, the increasing importance of the lungs as respiratory organs in _Protopterus_ and _Lepidosiren_ being associated with a corresponding reduction in the structural and functional development of the gills. There is no trace of spiracles in the adult. [Illustration: FIG. 165.—Transverse section through a branchial arch of _Neoceratodus_ (semi-diagrammatic), _a.b.a_, Afferent branchial artery; _b.a_, branchial arch; _b.f_, branchial filaments; _e.b.v_, efferent branchial vessel; _g.r_, gill-rakers. (From Baldwin Spencer.)] In _Neoceratodus_[294] there are five branchial clefts, including the hyobranchial. Each of the first four branchial arches carries a pair of hemibranchs, and, as in the Holocephali, the gill-lamellae are attached along nearly their whole length to a well-developed interbranchial septum (Fig. 165). A peculiarity of _Neoceratodus_, which has no counterpart in any other Fishes, is the extension of the branchial lamellae on to the dorsal and ventral walls of the branchial clefts, so that the hemibranchs on opposite sides of each cleft are continuous both dorsally and ventrally (Fig. 166). The fifth arch is gill-less. {286}In addition to the normal gills there is also a hyoidean pseudobranch. As in other Dipnoi, an operculum forms the outer wall of the branchial cavity, and leaves but a narrow, slit-like external branchial aperture. [Illustration: FIG. 166.—The second branchial cleft of _Neoceratodus_, to show the dorsal and ventral continuity of two hemibranchs on opposite sides of the same cleft. _b.c_, Branchial cleft; _b.f_, branchial filaments; _g.r_, gill-rakers. (From Baldwin Spencer.)]