X PREFACE. 



ance with the principle of arrangement of the Physiological depart- 

 ment of the Hunterian Museum, the Dental System is here traced 

 from its more simple to its more complex conditions. But this 

 progress is partially subordinated to the limits of zoological arrange- 

 ment. For, although the tooth of a Myliobates or a Labyrinthodon he, 

 in structure, more complex than many Mammalian teeth, yet this 

 complexity is associated with other characters, such as mode of 

 attachment, frequent shedding and renewal, &c., which indicate an 

 essentially inferior grade, and connect them, respectively, in closer 

 natural relationship with the more simple teeth of other species of 

 Fishes and Reptiles. A distinct Part, or division of the Work is, 

 therefore, appropriated to the Dental System of each of the three 

 great Classes of Vertebrated Animals which possess teeth. 



In the Mammalian series the course of progressive complication 

 of the teeth is closely followed, irrespective of the general grade of 

 organization of the species, and the Human dentition falls, accord- 

 ingly, into the middle of the series. Guided by the evidence of the 

 teeth I have sometimes deviated from the accepted Zoological systems, 

 as will be seen in the last Chapter, devoted to the complex den- 

 tition of the great Family of Hoofed herbivorous quadrupeds, 

 and especially in the value there assigned to the Ruminant modifica- 

 tion of the Ungulate type. 



In each Class, the chief characters of the teeth of the 

 extinct species are described in connection with those of the 

 allied existing forms. For so vast is now the extent, and so rapid 

 the progress of Palaeontology, and so important are the links in 

 the chain of Being thus recovered, that no treatise on the Compa- 

 rative Anatomy of the enduring parts of animals can fulfil its 

 expected purpose, if it be restricted to the description of such parts 

 in existing species alone. 



With regard to the Teeth, some of the most interesting and 

 extraordinary modifications were peculiar to species that have long 

 since passed away from the stage of animated existence ; and, 

 indeed, no comprehensive view could be obtained of the dental 

 tissues without a knowledge of those intermediate conditions which 



