TEETH. 



875 



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 

 In nit- Hi formes) 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 cuneati) are set 

 vertically in the upper pharyngeal bones of 

 the Parrot-fish (Scams, fig. 565.). A thin 



Fig. 565. 



Superior pharyngeal bones and teeth (Scarus). 



lamella, slightly curved like a finger-nail, is 

 the singular form of tooth in an extinct genus 

 of fishes, which I have thence called Pctalodits. 

 Sometimes the incisive form of tooth is notched 

 in the middle of the cutting edge, as in Sargus 

 imimaculalus. Sometimes the edge of the 

 crown is trilobate {Aplodactylus, fig. 566.). 



Fig. 566. 



Front teeth of ApJodactylus. 



Sometimes it is made quinquelobate by a 

 double notch on each side of the large middle 

 lobe (Bvops). In the formidable Sea-pike 



t Odontography, pi. 38, fig. 2 ; and art. PISCES, 

 Vol. III. p MO, fig. 517. 



(Sphyr&na Barracuda} the crown of each 

 tooth, large and small, is produced into a 

 compressed and sharp point, and resembles a 

 lancet. Sometimes the edges of such lancet- 

 shaped teeth are finely serrated, as in Priodon, 

 and the great Sharks of the genus Carcharias, 

 the fossil teeth of which indicate a species 

 (Carch. Megalodon) sixty or seventy feet in 

 length. 



The lancetted form is exchanged for the 

 stronger spear-shaped tooth in the Sharks of 

 the genus Lamna; and in the allied great ex- 

 tinct Olodus, as in the small Porbeagle, simi- 

 larly shaped, but stronger, piercing and cut- 

 ting teeth were complicated by one or more 

 accessory compressed cusps on each side their 

 base, like the Malay crease. 



With respect to situation, the teeth, in 

 Sharks and Rays, are limited to the bones 

 (maxillary and mandibular), which form the 

 anterior aperture of the mouth : in the Carp 

 and other Cyprinoids the teeth are confined 

 to the bones (pharyngeal and basi-occipital) 

 which circumscribe the posterior aperture of 

 the mouth. The Wrasses (Labrus) and the 

 Parrot-fishes (Scarus) have teeth on the 

 pre-maxillary and pre-mandibujar, as well as 

 on the upper and lower pharyngeals ; both 

 the anterior and posterior apertures of the 

 mouth being thus provided with instruments 

 for seizing, dividing, or comminuting the 

 food, the grinders being situated at the pha- 

 rynx. In most fishes teeth are developed 

 also in the intermediate parts of the oral 

 cavity, as on the palatines, the vomer, the 

 hyoid bones, the branchial arches; and, 

 though less commonly, on the pterygoids, the 

 entopterygoids, the sphenoids, and even on 

 the nasal bone (fig. 560, c.). It is very rare 

 to find teeth developed on the true superior 

 maxillary bones ; but the Herring and Salmon 

 tribes, some of the Ganoid Fishes, and the 

 great Sudis, are examples of this approach to 

 the higher Vertebrata. Among the anoma- 

 lous positions of teeth may be cited, besides 

 the occipital alveolus of the Carp *, the mar- 

 ginal alveoli of the prolonged, depressed, well 

 ossified rostrum of the Saw-fish, Prislis. 

 In the Lampreys and in Heloslomus (an os- 

 seous fish), most of the teeth are attached to 

 the lips. Lastly, it is peculiar to the class 

 Pisces^ amongst Vertebrata, to offer examples 

 of teeth developed in the median line of the 

 mouth, as in the palate of the Myxines (fig. 

 559, a.) ; or crossing the symphysis of the jaw, 

 as in Nolidanus, Scymnus, and Myliobales. 



Nor is the mode less varied than the place 

 of attachment. The teeth of Lophius, Pee- 

 cilia, Anablcps, are always moveable. In most 

 fishes they are anchylosed to the jaws by 

 continuous ossification from the base of the 

 dental pulp ; the histological transition being 

 more or less gradual from the structure of 

 the tooth to that of the bone. Sometimes 

 we find, not the base, but one side of the 

 tooth anchylosed to the alveolar border of the 

 jaw j and the teeth oppose each other by 



* Odontographv, pi. ,8; and, art. PISCES, Vol. III., 

 i& 



