. The Cambridge natural history. Zoology. 250 FISHES CHAP. like in many other respects, also has teeth implanted basally in the gums, and quite free from any special connexion with the jaw-hones. In some Teleosts with movable teeth, the latter are merely attached to the jaws by iibrous, and often elastic, ligaments, as in the Pike (Usox) and the Angler-Fish (Zophius). As a rule, however, the teeth are directly ankylosed to the bones developed in relation with the jaws. Very rarely, as, for example, in some Characinidae, are the teeth implanted in sockets. Xearly all Fishes are polyphyodont, th
. The Cambridge natural history. Zoology. 250 FISHES CHAP. like in many other respects, also has teeth implanted basally in the gums, and quite free from any special connexion with the jaw-hones. In some Teleosts with movable teeth, the latter are merely attached to the jaws by iibrous, and often elastic, ligaments, as in the Pike (Usox) and the Angler-Fish (Zophius). As a rule, however, the teeth are directly ankylosed to the bones developed in relation with the jaws. Very rarely, as, for example, in some Characinidae, are the teeth implanted in sockets. Xearly all Fishes are polyphyodont, that is, the old teeth are constantly replaced by new teeth as fast as they become worn down or fall out. In the Sharks and Dog-Fishes^ for example, where the teeth are arranged in rows parallel to the axis of each jaw, the functional teeth along the upper edge of the jaw are usually erect, while those iji the rows more internally situated point inwards towards the oral cavity; and behind these again there are rows of developing teeth in different stages of growth, and partially hidden beneath a projecting fold of the oral mucous membrane (Fig. 152). As the teeth in use become lost they are successively replaced by the inner rows, which, with the mucous Fig. 152.—Transverse section through membrane in which they are em- the jaw of a Shark [Carchdrias), i , , -, j, showing how the teeth are re- Dedaea, move lorwards to the edge placed, c. Cartilage of the jaw ; of the jaw, where they become erect t, fiinetiODal tooth ; t\ its ira- j i> • mediate ; t", t", still and functional The teeth of the younger teeth, covered by the Holocephali and of the Dipnoi are fold of mucous membrane, m. m. '^ jj^^wi ^io (From Eidewood.) not slied, but the loss which they sustain through wear and tear is made good by persistent growth at their bases. In the Teleo- stomi the succession is less regular, new teeth being formed between or at the bases of the old teeth. In the cas
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
