PART II. 



DENTAL SYSTEM OF REPTILES. 



CHAPTER I. 



GENERAL CHARACTERS OF THE TEETH OF REPTILES. 



67. Teeth, properly so called, do not exist in all reptiles; they are 

 absent in the whole order of Chelonia, in the Coluber scaher{\) among 

 the 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 vertebrae 

 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 for 

 the 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 thickness 

 and very dense ; its working surface is trenchant in the carnivorous 

 species, but variously sculptured and adapted for both cutting and 

 bruising 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, which 

 sink into alveolar cavities, regularly arranged (in Trionyx) along the 

 margins of the upper and lower jaw-bones : these alveoli are indicated 

 by the persistence of vascular canals long after the originally separate 

 tooth-like cones have become confluent and the horny sheath completed. 



The teeth of the dentigerous Saurian, Ophidian and Batrachian 

 reptiles, 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 Coraparee, Ed. 1835, torn. 1, p 340, 

 torn. 4, p. 617. 



N 2 



