10 EVOLUTION OF MAMMALIAN MOLAR TEETH 



ARRANGEMENT OF THIS VOLUME. 



The writer became interested in trituberculy while attempting to 

 monograph the Mesozoic mammals ; in course of this work many new 

 ideas came out, and many other ideas arose, apparently new, which 

 the writer subsequently found by more extensive reading had already 

 occurred to Professor Cope, and had been expressed in out-of-the-way 

 and unlooked-for places. 



The writer thus had the opportunity of fully developing the Mesozoic 

 origin of trituberculy , a part which Professor Cope had been obliged 

 to leave in the stage of suggestion. Subsequently the writer took up 

 the molar teeth of the monkeys and lemurs, and then of the hoofed 

 animals, which strangely enough form a perfect morphological succes- 

 sion of types, and thus enjoyed the opportunity of working out \vhat 

 might be called the secondary and tertiary addition, suppression, or 

 modification of cusps as illustrated in the modern Carnivores and 

 Ungulates. These papers are republished here in chronological order 

 with editorial notes. All corrections and insertions by the Editor are 

 indicated in [ ] brackets. All figure references are to figures as arranged 

 and numbered in this volume. The original pagination of the reprinted 

 essays is not given. 



Certain of the more purely philosophical and biological questions, 

 as distinguished from the anatomical, that is, matters of causation and 

 of evolution theory, are touched upon at one or two points in these 

 pages, but are more fully treated in another volume of these collected 

 papers, entitled Rectigradations in Evolution (cf. pp. 228-239). 



