GENERAL CHARACTERISTICS. 



jaws by two or more roots ; while in no cases are their crowns complicated by the 

 presence of infoldings of enamel. The simplest type of reptilian tooth is in the 

 form of a cone ; such conical teeth being confined to the margins of the jaws, 

 where, as among crocodiles, they may be implanted in distinct sockets, or, as in 

 the extinct fish -lizards, 

 in an open groove. In 

 other cases, as among 

 lizards, teeth of the same 

 general type may be 

 united by a bony deposit 

 either to the summit or 

 to one side of the margin 

 of the jaw. In place 

 of the one regular re- 

 placement, characteris- 

 ing the anterior teeth of 

 the majority of Mam- 

 mals, the teeth of most 

 Reptiles are replaced 

 irregularly and continu- 

 ously throughout life ; 

 the successional teeth 



growing up beneath the bases of those in use, and gradually causing an absorp- 

 tion of their roots. When teeth are distributed over the whole or a greater 

 portion of the palate, they generally assume a more or less flattened and bean- 

 like shape, so as to form a kind of pavement in the mouth, as shown in the 

 accompanying figure of the under surface of the skull of an extinct reptile. 



CONICAL TOOTH OF AN 

 EXTINCT PLESIO- 

 SAUEIAN REPTILE. 



UNDER SURFACE OF SKULL OF AN EXTINCT 



REPTILE (Cyamodus), WITH PAVEMENT - LIKE 



TEETH ON THE PALATE. 



LEFT SIDE OF THE SKULL OF A BEAKED FLYING DRAGON (& nat. size). 



a, vacuity in front of the eye ; 6, socket of the eye ; c, occipital spine ; d, angle of lower jaw ;e, extremity of 

 upper, and e', of lower jaw ; q, articulation of the skull proper with the lower jaw ; *, point whe 

 of the lower jaw diverge. After Marsh. 



Between conical and pavement - like teeth there are various intermediate grades, 

 some of which will be referred to in the sequel. It is, however, by no me; 

 all members of the class that are provided with teeth; the tortoises and 

 being living examples of the total loss of these organs, and the consequent convei 



