TEETH. 



883 



Ophidian, and Batrachian reptiles, are, for the 

 most part, simple and adapted for seizing and 

 holding, but not for dividing or masticating 

 their food. The Siren alone combines true 

 teeth with a horny maxillary trenchant sheath, 

 like that of the Chelonian reptiles. 



With respect to number, in no existing rep- 

 tile are the teeth reduced so low as in certain 

 mammals and fishes ; nor, on the other hand, 

 are they ever so multiplied as in many of 

 the latter class. The extinct Dicynodont 

 reptiles of South Africa had hut two teeth, 

 which were long tusks implanted in the upper 

 jaw.* Some species of Amphisbaina (A. alba], 

 with fifteen teeth in the upper jaw and four- 

 teen in the lower jaw, and certain Monitors 

 ( farftnits], with sixteen teeth in the upper and 

 fourteen in the lower jaw, afford examples of 

 the smallest number of teeth amongst existing 

 reptiles ; and certain Batrachians, with teeth 

 " en cardes " at the roof of the mouth, or 

 which have upwards of eighty teeth in each 

 lateral maxillary series, present the largest 

 number. It is rarely that the number of the 

 teeth is fixed and determinate in any reptile 

 so as to be characteristic of the species, and 

 still more rarely have the individual teeth 

 such characters as to be determined homo- 

 logically from one species to another. 



With respect to situation, the teeth may be 

 present on the jaws only, i.e. the maxillary, pre- 

 maxillary, and mandibular bones, as in the croco- 

 diles and many lizards : or upon the jaws and 

 roof of the mouth ; and here either upon the 

 pterygoid bones, as in the Iguana and Mosa- 

 saur, or upon both palatine and pterygoid 

 bones, as in most serpents, or upon the 

 vomer, as in most Batrachians, or upon both 

 vomerine and pterygoid bones, as in the Axo- 

 lote ; or upon the vomerine and sphenoid 

 bones, as in the Salamandra glutinosa, Maclure. 

 With respect to the marginal or jaw teeth, 

 these may be absent in the intermaxillary 

 bones, as in many serpents ; or they may be 

 present in the upper and not in the lower 

 jaw, as in most frogs ; or in both upper and 

 lower jaws, as in the tailed Batrachians ; and 

 among these they may be supported, upon 

 the lower jaw, by the premandibular or den- 

 tary piece, as in the Salamanders, Menopome, 

 Amphiume, Proteus ; or upon the splenial 

 piece, as in the Siren ; or upon both splenial 

 and premandibular bones, as in the Axolotl. 

 The palatine and pterygoid teeth may, in the 

 Batrachians, be arranged in several rows, like 

 the " dents en cardes " of fishes. The sphe- 

 noid and splenial teeth are always so ar- 

 ranged in the few species that possess them. 

 The intermaxillary, maxillary, and preman- 

 dibular teeth are uniserial, or in one row, with 

 the exception of the Caecilia and the extinct 

 Labyrinthodonts, which have a double row of 

 teeth at the anterior part of the lower jaw. 



The teeth of reptiles, with few exceptions, 

 present a simple conical firm, with the crown 

 more or less curved, and the apex more or 



* Transactions of the Geological Society, 2cl series, 

 vol. vii., 1845, p. 59. 



less acute. The cone varies in length and 

 thickness ; its transverse section is sometimes 

 circular, but more commonly elliptical or oval, 

 and this modification of the cone may be 

 traced through every gradation, from' the 

 thick, round, canine-like tooth of the croco- 

 dile, to the sabre-shaped fang of the Varanus, 

 the Megalosaur, and the Cladeiodon.* Some- 

 times, as in the fully formed teeth of the 

 Megalosaur, one of the margins of the com- 

 pressed crown of the tooth is trenchant, 

 sometimes both are so ; and these may be 

 simply sharp-edged, as in the Varanus of 

 Timor, or finely serrated, as in the great Va- 

 ranus, the Cladeiodon, and the Megalosaur.-f- 



The outer surface of the crown of the 

 tooth is usually smooth ; it may be polished, 

 as in the Leiodon, or impressed with fine 

 lines, as in the Labyrinthodon (jig. 551.), or 

 raised into many narrow ridges, as in the 

 Plciosaur and Polyptychodon, or broken by a 

 few broad ridges, as in the Iguanodon (Jig. 

 571.), or grooved by a single longitudinal 

 furrow, as in some serpents (fig. 509, A). 



The cone is longest and its summit sharpest 

 in the serpents : from these may be traced, 

 chiefly in the lizard tribe, a progressive short- 

 ening, expansion of the base, and blunting of 

 the apex of the tooth, until the cone is 

 reduced to a hemispherical tubercle, or plate, 

 as in the Thorictes and Cyclodus (Jig. 570.). 



In the Pleiosaur the dental cone is three- 

 sided, with one of the angles rounded off. 

 The posterior subcompressed teeth of the 

 alligator (Jig. 573.) present a new modification 

 of form ; here they terminate in a mammillate 

 summit, supported by a slightly constricted 

 neck. In the tooth of the Hylceosaur the 

 expanded summit is flattened, bent, and spear- 

 shaped, with the edges blunted. But the 

 expansion of the crown is greatest in the sub- 

 compressed teeth of the extinct Cardiodon and 

 the existing Iguanas, the teeth of which are 

 farther complicated by having the margins 

 notched. The great Iguanodon had the crown 

 of the tooth expanded both in length and 

 breadth, and combining marginal dentations 

 with longitudinal ridges : this tooth (fig. 571.) 

 presents the most complicated external form 

 as yet discovered in the class of reptiles. 



In no reptiles does the base of the tooth 

 ever branch into fangs. 



Attachment. As a general rule, the teeth 

 of reptiles are anchylosed to the bone which 

 supports them. When they continue distinct, 

 they may be lodged either in a continuous 

 groove, as in the Ichthyosaur , or in separate 

 sockets, as in the Plesiosaur and Oocodilians 

 (fig. 573.). The base of the tooth is anchy- 

 losed to the walls of a moderately deep socket 

 in the extinct Megalosaur and Theocodon. 

 In the Labyrinthodonts and Caecilioe, among 

 the Bratrachians ; in most Ophidians ; and 

 in the Geckos, Agamians, and Varanians, 

 among the Saurians, the base of the tooth is 



* Odontography, pi. 02 A, fig. 4. 

 f lb.fg.6c. 



j Ib. pi. 65 ; vol. iv.,frjs. 209, 210. 

 Ib. pi. 13,^. 9. 



3L 2 



