46 ORAL EQUIPMENTS. 



One point only might be noted. The teeth are attached 

 by ankylosis, each tooth being perched on a little pedestal 

 of bone specially formed for it. As the new tooth advances 

 it causes absorption of the inner wall of this bone, and of 

 the tooth, and finally takes its place actually in the pulp- 

 chamber of its predecessor, which it pushes out on its 

 point. 



Newts and Salamanders are fairly normal. 



Saurian reptiles, i.e., lizards, &c, have an endless succes- 

 sion of rounded conical teeth, for the most part confined to 

 the margins of the jaws. 



Crocodiles and Alligators are remarkable for having 

 socketed teeth, attached by " gomphosis." They are somewhat 

 trihedral, but single pointed teeth, with certain ones specially 

 developed ; which varies according to the species. The teeth 

 succeed each other vertically, each new tooth coming directly 

 into the socket of its predecessor, which it displaces. There 

 are never any additions numerically made, as the age of the 

 creature advances. 



But amongst the Ophidia we find some of the most 

 remarkable differentiations of structure of the teeth in rela- 

 tion to the function they have to perform. In fact, so 

 remarkable do I consider the poison-fangs of the Viperine 

 snakes, that I have honoured them with a very special des- 

 cription, and several careful drawings, as I cannot get any 

 specimens in the museum ; and I unfortunately presented my 

 own collection of skulls to the museum of my old College in 

 London, about two years ago. 



The dentition of the Ophidians is very uniform. They 

 may be conveniently divided into two groups — the poisonous 

 and non-poisonous or harmless snakes. Between these 

 groups are many forms which unite in their persons some of 

 the attributes of both these groups, in a modified degree. 

 Thus for instance we may say, speaking roughly, that the 

 teeth decrease in number the more venomous the snake, and 

 vice versa ; that the poison groove of the poison fang, which 

 in venomous snakes forms a complete tube, becomes less 

 and less deep amongst the more harmless species, and ceases 

 to be differentiated at all in the typical harmless ones and 

 is fixed immovably, and the tooth erectile ; and that the 

 " quadrate bones," of which more anon, are longer, and con- 

 sequently the " gape" of the jaws is larger, the nearer we 

 approach the true Vipers. 



The semi- venomous snakes are called " Colubrine" poi- 

 sonous snakes, after the " Coluber," a species of harmless 



