That the dentine is the ossified pulp is an older notion than that it is an inorganic secretion from such pulp. But an hypo thesis, to be of any value in science, must be proved. Almost every true theory has been indicated, with various degrees of approxi mation, before its final establishment : but he has ever been held, in exact philosophy, to be the author of a theory, by whom it has been first rightly enunciated and satisfactorily established. When time has dissipated the mists of individual or national rivalries and jealousies, the name of the true discoverer is clearly seen by the inextinguishable light of true and impartial history : and to that period I look forward with calm and confident hope.
I proceed now to briefly point out the leading characteristics of the teeth in the dif ferent classes of the vertebrate animals.
Dental System of Fishes.
The teeth of fishes, whether we study them in regard to their number, form, substance, structure, situation, or mode of attachment, offer a greater and more striking series of varieties than do those of any other class of animals.
As to number, they range from zero to countless quantities. The Lancelet, the Am mocete, the Sturgeon, the Paddle-fish, and the whole order of Lophobranchii, are eden tulous. The Myxinoids have a single pointed tooth on the roof of the mouth (fig. 559., a), and two serrated dental plates (6) on the tongue. The Tench (fig. 514. Vol. III. p. 979. art. Pisces)* has a single grinding tooth on the occiput (c), opposed to two denti gerous pharyngeal jaws below (dd). In the Lepidosiren a single maxillary dental plate (fig. 560., a) is opposed to a single mandibular one (b), and there are two small denticles on the nasal bone (c). In the extinct Sharks with crushing teeth, called Ccratodua and Cie nodus, the jaws were armed with four teeth, two above and two below.f In the Chinuerce, two mandibular teeth are opposed to four maxillary teeth.t From this low point the number in different fishes is progressively multiplied until, in the Pike, the Siluroids (fig. 561.), and many other fishes, the mouth becomes crowded with countless teeth.
With respect to form, I may first observe, that as organised beings withdraw themselves more and more, in their ascent in the scale of life, from the influence of the general polarising forces, so their parts progressively deviate from geometrical figures : it is only, therefore, in the lowest vertebrated class that we find teeth in the form of perfect cubes, and of prisms or plates with three sides (.11Tyletes), four sides (Scares), five or six sides, .11/1:ylio bates (fag. 562.). The cone is the most com mon form in fishes : such teeth may be slender, sharp-pointed, and so minute, numerous, and closely aggregated, as -to resemble the plush or pile of velvet ; these are called teeth" (denies oil/norms, dents en velours§); all the teeth of the Perch are of this kind : when the teeth are equally fine and numerous, but longer, they are called " ciliiform " (denies recurved, as in the Mumma ; or barbed, as in Trieldurus, and some other Scomberoids ; or it may be bent upon itself, like a tenterhook, as in the fishes thence called (ioniodonts.* In the Bonito may be perceived a progressive thickening of the base of the conical teeth : and this being combined in other predatory ciliiprnies): when the teeth are similar to, but rather stronger than these, they are called fishes with increased size and recurved direc tion, they then resemble the laniary or canine teeth of carnivorous quadrupeds, as we see in the large teeth of the Pike, in the Lophiust, and in certain sharks.$
The anterior diverging grappling teeth of the wolf-fish form stronger cones ; and by progressive blunting, flattening, and expansion of the apex, observable in different fishes, the cone gradually changes to the thick and short cylinder, such as is seen in the back " setiform" (denies setifornies, denies en brosse): conical teeth, as close set and sharp pointed as the villiform teeth, but of larger size, are called " rasp-teeth" (denies radulformes, dents en rape or en eardes, fig. 561.); the Pike pre sents such teeth on the back part of the vomer the teeth of the Sheat•fish (Mums glanis) present all the gradations between the villi form and raduliforni types. Setiform teeth are common in the fishes thence called Chae todonts* ; in the genus Citbarina they bifur cate at their free extremities ; in the genus Platax they end there in three diverging points (fig. 563.), and the cone here merges into the long and slender cylinder. Some times the cone is compressed into a slender trenchant blade : and this may be pointed and teeth of the wolf-fish, and in similar grinding and crushing teeth in other genera, whether feeders on sea-weeds, or crustaceous and testa ceous animals. The grinding surface of these short cylindrical teeth may be convex, as in the Sheep's-head fish (Sargus); or 'flattened, as in the pharyngeal teeth of the Wrasse (La brus).§ Sometimes the hemispheric teeth are so numerous, and spread over so broad a sur face, as to resemble a pavement, as in the pharyngeal bones of the Wrasse or Rock-fish (Labrus, fig. 564.) ; or they may be so small, as well as numerous (denies ,granfformes), as to give a granulated surface to the part of the mouth to which they are attached (premax illaries of Cossypbus),II A progressive increase of the transverse over the vertical diameter may be traced in the molar teeth of different fishes, and sometimes in those of the same individual, as in Labrus (fig. 564.), until the cylindrical form is exchanged for that of the depressed plate. Such dental plates (denies lamellifOrntes) may be found, not only circular, but elliptical, oval, semilunar, sigmoid, oblong, or even square, hexagonal, pentagonal, or tri angular; and the grinding surface may present various and beautiful kinds of sculpturing. The broadest and thinnest lamelliform teeth are those that form the complex grinding tubercle of the Diodon.# The front teeth of the Flounder and Sargus present the form of compressed plates, at least in the crown, and are true denies incisivi. Numerous wedge shaped dental plates (denies euneati) are set vertically in the upper pharyngeal bones of the Parrot-fish (Scams, fig. 565.). A thin lamella, slightly curved like a finger-nail, is the singular form of tooth in an extinct genus of fishes, which I have thence called Petalodus. Sometimes the incisive form of tooth is notched in the middle of the cutting edge, as in Sargus uninmeulatus. Sometimes the edge of the crown is trilobate (Aplodactylus, fig. 566.).