256 TEETH OF POISONOUS SNAKES. 



partly absorbed or eaten away, as at «, Fig. 65; and 

 Avitbin tbe cavity will be seen tbe lialf-formed succeeding 

 tooth, h; at tlie base of which may probably be found the 

 beginning or germ, c, of the successor of that tooth ; all 

 the teeth in the crocodile tribe being pushed out and re- 

 placed in the vertical direction by new teeth, as long as 

 they live. The individual teeth increase in size as the 

 animal grows; but the number of teeth remains the same 

 from the period when the crocodile quits the Qgg to the 

 attainment of its full size and age. No sooner has the 

 young tooth penetrated the interior of the old one, than 

 another germ begins to be developed from the angle be- 

 tween the base of the young tooth and the inner alveolar 

 process, or in the same relative position as that in which 

 its immediate predecessor began to rise ; and the processes 

 of succession and displacement are carried on, uninter- 

 ruptedly, throughout the long life of these cold-blooded 

 carnivorous reptiles. The fossil jaws of the extinct 

 crocodiles demonstrate that the same law regulated the 

 succession of the teeth at the ancient epochs when they 

 prevailed in greatest numbers, and under the most varied 

 specific modifications, as at the present day, when they 

 are reduced to a single family. 



The most complex condition of the dental system in 

 the reptile class is that which is presented by the poison- 

 ous serpents, in which certain teeth are associated with 

 the tube or duct of a poison bag and gland. 



These teeth, called "poison-fangs," are confined to those 

 bones of the upper jaw called "maxillary," and are 

 usually single; or, when more, one only is connected 

 with the poison-apparatus, and the others are either 

 simple teeth, or preparing to take the place of the poi- 

 son-fang-. 



