XVII] THE COMPARISON OF RELATED FORMS 1075 



By similar and not more violent changes we pass easily to suca 

 allied forms as the Titanotheres (Fig, 541); and the well-known 

 series of species of Titanotherium, by which Professor Osborn has 



JFig. 540. Occipital view of the skulls of various extinct rhinoceroses 

 (Aceratherium spp.). After Osborn. 



illustrated the evolution of this genus, constitutes a simple and 

 suitable case for the application of our method. 



But our method enables us to. pass over greater gaps than these, 

 and to discern the general, and to a very large extent even the 



Fig. 541. Titanotherium rohiLstum. Fig. 542. Tapir's skull. 



detailed, resemblances between the skull of the rhinoceros and those 

 of the tapir or the horse. From the Cartesian coordinates in which 

 we have begun by inscribing the sfcull of a primitive rhinoceros, 

 we pass to the tapir's skull (Fig. 542), firstly, by converting the 



