A treatise on zoology . p, lateral plate ;, median anterior, and , median posterior plate ; , neural arch ; , cartilage ofneural arch ; , not>ochordal sheath ; , neural spine ; vt, notochord ; o, opercular, and oc,Its cartilage ; pu, parasphenoid; pif, jiostfrontal; , pterygo-palatine; , palatine tooth ;pto, pterotic (?); and q, its downwaid process covering the quadrate cartilage, ; s, sub-opercular; so, suborbital; up, splenial; , splenial tooth ; , vomerine tooth. where the trabeculae remain recognisable, and the wall of the brain-case is to some ex
A treatise on zoology . p, lateral plate ;, median anterior, and , median posterior plate ; , neural arch ; , cartilage ofneural arch ; , not>ochordal sheath ; , neural spine ; vt, notochord ; o, opercular, and oc,Its cartilage ; pu, parasphenoid; pif, jiostfrontal; , pterygo-palatine; , palatine tooth ;pto, pterotic (?); and q, its downwaid process covering the quadrate cartilage, ; s, sub-opercular; so, suborbital; up, splenial; , splenial tooth ; , vomerine tooth. where the trabeculae remain recognisable, and the wall of the brain-case is to some extent formed In membrane l»ones above, beloAv,and at the sides (Fig. 209). The cavity of the auditory capsuleis widely open to the interior as in Teleostomcs. Fenestratedcartilaginous nasal capsules are present; also separate nasalcartilages, at all events in Ccmtodiis (Fig. 207). SKULL 237 It is ill the connection of the skull with the visceral arches thatthe Dipnoi have diverged most conspicuously from other fish. The. modern genera are completely autostylic (p. 95). The pterygo-quadrate bar is firmly fused to the cranium in front and spiracle disappears; and the hyoid arch is well developed, witha median basihyal, paired hypohyals, and large ossified ceratohj^als 238 DIPNOI (Fig. 206). But the hyomandibular takes no share in the supportof the jaws. It disappears, indeed, entirely in the Dipneumones,where the ceratohyals alone remain, and, as Huxley showed [230](Ridewood [358], Sewertzoff [408]), is represented in Ceratodns by aminute vestigial cartilage, overlying the hyomandibular branch ofthe seventh nerve (Fig. 206). Of the structure of the hyoid andbranchial arches in the fossil forms we know practically nothing, butthere is no reason to think that it differed essentially from that ofmodern Dipnoi. Tracj[uair has shown that Dipterus was autostylic[447]. The branchial arches in Ceratodus are fairly well developedwith epibranchial elements, and even some pharyng
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
