PART II.

DENTAL SYSTEM OF REPTILES.

CHAPTER I.

GENERAL CHARACTERS OF THE TEETH OF REPTILES.

G7. Teeth, properly so called, do not exist in all reptiles; they areabsent in the whole order of Chelonia , in the Coluber scaber ( 1) amongthe Ophidia, and in the toads among the Batrachia. In the latter eden-tulous reptiles there is no compensating structure ; but in the Coluber scaber , the inferior spinous processes of certain of the cervical vertebra;are unusually prolonged, and penetrate the coats of the oesophagus ;their extremities, which are thus introduced into the alimentary canal,are coated with a layer of hard dentine, and form substitutes forthe teeth, which, if not always entirely absent, are merely rudi-mental in the ordinary situations in the mouth. (2)

In the tortoises and turtles the jaws are covered, as is well known,by a sheath of horn, which in some species is of considerable thicknessand very dense ; its working surface is trenchant in the carnivorousspecies, but variously sculptured and adapted for both cutting andbruising in the vegetable feeders.

The development of the continuous horny maxillary sheath com-mences, as in the parrot-tribe, from a series of distinct papillae, whichsink into alveolar cavities, regularly arranged (in Trionyx) along themargins of the upper and lower jaw-bones : these alveoli are indicatedby the persistence of vascular canals long after the originally separatetooth-like cones have become confluent and the horny sheath completed.

The teeth of the dentigerous Saurian, Ophidian and Batrachianreptiles, are, for the most part simple and adapted for seizing and

(1) Hence called Anodon typus by Dr. Smith.

(2) Dr. Jourdan, in Cuvier , Lemons d’Anatomie Comparee, Ed. 1835 , tom. 1, p 340 ,tom. 4 , p. 617 .

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