100 COMPAEATIVE DENTAL ANATOMY 



and the points sharp as in the snakes; or short 

 and blunt as in the crocodiles; or tubercular, as 

 in some lizards, etc. 



Teeth do not exist in all reptiles, as one whole 

 order, the Chelonia, and some snakes are eden- 

 tulous. They may be present on the jaws only, 

 — as in the crocodiles, lizards etc., — or upon the 

 palatine and pterygoid bones, or the intermaxil- 

 laries. Some toothless snakes have the inferior 

 spinous processes of certain cervical vertebrae 

 prolonged to project within the walls of the 

 oesophagus for the crushing of the shells of eggs 

 on which such species feed. The teeth are usually 

 implanted in sockets in the true Reptiles, though 

 the lizards and snakes often have them ankylosed 

 to the jaw. The root is single, and never 

 branches into fangs as in the mammals. They 

 are continuous in succession like the teeth of 

 Fishes and Batrachians, and this proceeds through 

 life, teeth being shed and replaced without cessa- 

 tion. The teeth are composed of hard dentin 

 with a thin layer of enamel on the apex. 



The Lacertilia comprises the Lizards, Chame- 

 leons, Iguanas, etc. The Iguanodon and other 

 great extinct lizards are also related to this order. 

 They are distinguished from the other reptiles 

 mainly by the presence of clavicles. The skull is 

 intermediate between crocodiles and turtles. The 

 teeth are attached by ankylosis, like the Batra- 



