66 THE GENEALOGY OF THE VERTEBRATA. 



Anura 



Urodela Trachystomata 



I 

 Proteida 



i 

 i 



Stegocephali 

 Embolomeri Rhachitomi 



Ganocephala 1 



An examination of the above tables shows that there 

 has been in the history of the Batrachian class a reduc- 

 tion in the number of the elements composing the skull, 

 both by loss and by fusion with each other. It also 

 shows that the vertebrae have passed from a notochordal 

 state with segmented centra, to biconcave centra, and 

 finally to ball and socket centra, Avith a great reduction 

 of the caudal series. It is also the fact that the earlier 

 forms (those of the Permian epoch) show the most rep- 

 tilian characters of the tarsus and of the pelvis. The 

 later forms, the salamanders, show a more specialized 

 form of carpus and tarsus and of pelvis also. In the 

 latest forms, the Anura, the carpus and tarsus are re- 

 duced through loss of parts, except that the astragalus 

 and calcaneum are phenomenally elongate. We have 

 then, in the Batrachian series, a somewhat mixed kind 

 of change ; but it principally consists of concentration 

 and consolidation of parts. The question as to whether 

 this rjrocess is one of progression or retrogression may 

 be answered as follows : If degeneracy consists in "the 

 loss of parts without complementary addition of other 

 parts," then the Batrachian line is a degenerate one. 

 This is only partly true of the vertebral column, which 

 presents the most primitive characters in the early, Car- 

 boniferous, genera (Rhachitomi). If departure from the 



1 Includes Trimerorhaehidie aud Archegosauridae. 



50 



