PHYLOGENY. 



in 



imation to the Mammalia is degeneracy, then the 

 changes in this class come partly under that head. The 

 scapular and pelvic arches of the Rachitomi are more 

 mammalian than are those of any of their successors ; 



Fig. 27. Crzcotus crassidiscus Cope, parts of individual represented in 

 Fig. 28; one-third natural size. From Permian of Texas, a, head from above; 

 b, part of belly from below. From Cope. 



the carpus and tarsus are less so than that of the 

 Anura. 



There are several groups which show special marks 

 of degeneracy. Such are the reduced maxillary bones 



