In many fishes, e. g. Lophius, Esox, the dental papillae become buried in the membrane from which they rise, and the surface to which their basis is attached becomes the bottom of a closed sac : but this sac does not become inclosed in the substance of the jaw ; so that teeth at different stages of growth are brought away with the thick and soft gum, when it is stripped from the jaw-bone. The final fix ation of teeth, so formed, is effected by the development of ligamentous fibres in the sub-' mucous tissue between the jaw and the base of the tooth, which fibres become the medium of connection between those parts, either as elastic ligaments, or by continuous ossifi cation. Here, therefore, is represented the " follicular " stage of the development of a mammalian tooth ; but the " eruptive " stage takes place without previous inclosure of the follicle and matrix in the substance of the jaw-bone.
In Batistes, Scants, Sphyrcena, the Sparoids, and many other fishes, the formation of the teeth presents all the usual stages which have been observed to succeed each other in the dentition of the higher Vertebrata: the papilla sinks into a follicle, becomes surrounded by a capsule, and is then included within a closed alveolus of the growing jaw (fig. 516. c, Vol. III. p. 979. art. PISCES), where the de velopement of the tooth takes place and is followed by the usual eruptive stages. A distinct enamel-pulp is developed from the inner surface of the capsule in Bailees, Scares, Barges, and Chrysophrys.
The most formidable dentition exhibited in the order of osseous fishes, is that which cha racterises the Sphyrcena, and some extinct fishes allied to this predatory genus. In the great Barracuda of the southern shores of the United States (Sphyrcena Barracuda, Cuv.), the lower jaw contains a single row of large, compressed, conical, sharp-pointed, and sharp edged teeth, resembling the blades of lancets, but stronger at the base. The two anterior of these teeth are twice as long as the rest, but the posterior and serial teeth gradually increase in size towards the back part of the jaw ; there are about twenty-four of these piercing and cutting teeth in each preman dibular bone. They are opposed to a double row of similar teeth in the upper jaw, and fit into the interspace of these two rows when the mouth is closed. The outermost row is situated on the intermaxillary, the innermost on the palatine bones ; there are no teeth on the vomer or superior maxillary bones. The two anterior teeth in each premaxillary bone equal the opposite pair in the lower jaw in size : the posterior teeth are serial, numerous, and of small size ; the second of the two an terior large premaxillary teeth is placed on the inner side of the commencement of the row of small teeth,' and is a little inclined backwards. The retaining power of all the
large anterior teeth is increased by a slight posterior projection, similar to the barb of a fish-book, but smaller. The palatine bones contain each nine or ten lancet-shaped teeth, somewhat larger than the posterior ones of the lower jaw. All these teeth afford good examples of the mode of attachment by im plantation in sockets, which has been denied to exist in fishes.* The loss or injury to which these destruc tive weapons are liable in the conflict which the ASphyrcena wages with its living and struggling prey, is repaired by an uninter rupted succession of new pulps and teeth. The existence of these is indicated by the foramina, which are situated immediately posterior to, or on the inner margin of, the sockets of the teeth in place ; these foramina lead to alveoli of reserve, in which the crowns of the new teeth in different stages of de velopment are loosely embedded. It is in this position of the germs of the teeth that the Sphyrmnoid fishes, both recent and fossil, mainly differ, as to their dental characters, from the rest of the Scomberoid family, and proportionally approach the Sauroid type. The base or fang of the fully-developed tooth of the Sphyrcenz is anchylosed to the parietes of the socket in which it is inserted. The pressure of the crown of the new tooth ex cites absorption of the inner side of the base of the old, which thus finally loses the requi site strength of attachment ; and its loss is followed by the absorption of the old socket, as in the higher animals.
It is interesting to observe that the alter nate teeth are, in general, contemporaneously shed ; so that the maxillary armour is always preserved in an effective state. The relative position of the new teeth to their predecessors, and their influence upon them, resembles, in the Sphyrcena, some of the phenomena which will be described in the dentition of the cro codilian reptiles. To the crocodiles the pre sent voracious fish also approximates in the alveolar lodgment of the teeth ; but it mani fests its ichthyic character in the anchylosis of the fully-developed teeth to their sockets, and still more strikingly in the intimate struc ture of the teeth.