PHYLOGENY. 109 



period. From that time they diminish in numbers, 

 and at the present day form an insignificant part of 

 the vertebrate fauna of the earth. The history of their 

 succession is told by a table of classification such as I 

 give below : 



I. Supraoccipital, tabular, and supramastoid bones present. Pro- 

 podial bones distinct. Stegocephali. 



Vertebral centra, including atlas, segmented, one set of 

 segments together supporting one arch ; Rhachitomi. 



Vertebrae segmented, the superior and inferior segments 

 each complete, forming two centra to each arch ; 



Embolomeri. 



Vertebral centra, including atlas, not segmented, one to 

 each arch; Microsauri, 



II. Supraoccipital and supramastoid bones wanting. Frontal and 

 propodial bones distinct ; Urodela. 



a. An OS tabulare. 



A palatine arch and separate caudal vertebrae ; Protdda 

 aa. No OS tabulare. 



A maxillary arch ; palatine arch imperfect ; nasals, pre- 

 maxillaries and caudal vertebrae distinct ; 



Pseudosauriay 



No maxillary or palatine arches ; nasals and premaxil- 



liary, also caudal vertebrae, distinct ; Trachystomata. 



III. Supraoccipital, tabular, and supramastoid bones wanting. 

 Frontals and parietals connate ; propodial bones and caudal 

 vertebrae confluent ; Salientia. 



Premaxillaries distinct from nasals ; no palatine arch ; 

 astragalus and calcaneum elongate, forming a distinct 

 segment of the limb ; Anura. 



The probable phylogeny of these orders as imper- 

 fectly indicated by paleontology is exhibited in the 

 diagram on the following page. 



An examination of the above tables shows that 

 there has been in the history of the batrachian class a 

 reduction in the number of the elements composing 



1 Includes the Gymnophiona. 



