178 DINOCERATA. 



These facts lie at the foundation of classification, and it is only by 

 keeping the two series of characters sejaarate, that the true relationship 

 between different groups of animals can be made out, and their genealogy 

 indicated with any probability. 



Bearing this in mind in considering the Dinocerata, we must first seek 

 to ascertain what general characters they have inherited from ancestral 

 forms, and next what special characters they have since acquired. The 

 relation of the group to the orders of existing Ungulates will then be 

 indicated by ascertaining what characters, derived from a common 

 ancestry, they share with each other, and what special characters, due, 

 perhaps, to influences of similar nature, they possess in common. 



We have seen that the primitive Mammals (Hi/potJicria) must have 

 possessed a large number of general characters, some of which have 

 already been given in the list on page 170. The primitive Ungulates 

 (Protungulata), starting off" on a particular line from the preceding type, 

 would naturally retain nearly all these general characters, as indicated 

 in the list on page 171. Each of the great branches that passed ofi" from 

 this 2^iirent stem retained a certain number of these primal characters, and 

 some of them we find in the Ungulates of to-day. 



The characters possessed by the Holodactyla were most of them still 

 the ancestral features, and the Amhlydactyla, on the line toward the 

 Binocerata, shared many of the same characters. 



The Binocerata, representing a further stage of progress, had still as 

 their inheritance a number of persistent general characters. Some of 

 these characters are the following : 



(1.) Brain, small and smooth. 



(2.) Orbit open behind. 



(3.) Post-glenoid process. 



(4.) Alisphenoid canal. 



(5.) Vertebra?, flat. 



(6.) Odontoid process, conical. 



(7.) Sternum, flat. 



(8.) Feet, plantigrade. 



