. On the anatomy of vertebrates [electronic resource] . e Diverging Appendage of the tympano-mandibular archconsists of the bones which support the gill-cover, a kind of shortand broad fin, the movements of which regulate the passage ofthe currents through the branchial cavity, opening and closing thebranchial aperture on each side of the head. The first of these6 opercular bones is the preopercular, fig. 75, 34, which is usuallythe longest in the vertical direction. In the Gurnards, or mailed-cheeked Fishes, fig. 82, the preopercular is articulated with theenormously developed suborbital scal
. On the anatomy of vertebrates [electronic resource] . e Diverging Appendage of the tympano-mandibular archconsists of the bones which support the gill-cover, a kind of shortand broad fin, the movements of which regulate the passage ofthe currents through the branchial cavity, opening and closing thebranchial aperture on each side of the head. The first of these6 opercular bones is the preopercular, fig. 75, 34, which is usuallythe longest in the vertical direction. In the Gurnards, or mailed-cheeked Fishes, fig. 82, the preopercular is articulated with theenormously developed suborbital scale bone, 73. Three bones usually constitute the second series of thisappendage: the upper one is commonly the largest and of atriangular form, thin and with radiated lines like a scale: it isthe opercular, figs. 75, 84, 35 : in the Cod it is principally connectedwith the posterior margin of the preopercular, and below with thesubopercular, ib. 36; but it has usually, also, a partial attachmentto the outer angle of the epitympanic, fig. 84; and is some-. Lower jaw, (Arapaima ijiijas) 124 ANATOMY OF VERTEBRATES. times (Diodo?i, Lophius, Anguilla) exclusively suspended the Lophius piscatorius the opercular is a long and strong bonesuspended vertically from the convex epitympanic condyle, andwith a long and slender fin-ray proceeding from the back part ofthat joint. The subopercular forms the chief part of the opercularfin by its long backwardly produced lower angle. The sub-opercular bone in the Conger is soon reduced to a mere ray,which curves backwards and upwards like one of the branchio-stegals. The opercular itself, though shorter and retaining moreof its laminated form, also shows plainly, by its length and curva-ture in the Eels, its essential nature as a metamorphosed ray ofthe tympanic fin. We have seen that all the framework of thisfin had the form of rays in the Plagiostomes. In Murcena thesmall opercular bones articulate only to the under half of thetympani
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