PREFACE XI 



A book of this character is obviously not the proper place for 

 polemical discussions of disputed questions. Whenever, there- 

 fore, the views expressed differ widely from those maintained by 

 other palaeontologists, I have attempted no more than to state, as 

 fairly as I could, the alternative interpretations and my own 

 choice between them. Any other course was forbidden by the 

 limitations of space. 



It is a pleasure to give expression to my sincere sense of grati- 

 tude to the many friends who have helped me in an unusually 

 laborious undertaking. Professor Osborn and Dr. Matthew have 

 placed at my disposal the vronderful treasures of the American 

 Museum of Natural History in New York and in the most liberal 

 manner have supplied me with photographs and specimens for 

 drawings, as well as with information regarding important dis- 

 coveries v^hich have not yet been published. Dr. W. J. Holland, 

 Director of the Carnegie Museum in Pittsburgh, has likewise gen- 

 erously provided many photographs from the noble collection under 

 his charge, kindly permitting the use of material still undescribed. 

 To Professor Charles Schuchert, of Yale University, I am also 

 indebted for several photographs. 



The figures of existing animals are almost all from photographs 

 taken in the New York and London zoological gardens, and I 

 desire to thank Director Hornaday, of the Bronx Park, and Mr. 

 Peacock, of the London garden, for the very kind manner in 

 which they have procured these illustrations for my use. The 

 photographs have been modified by painting out the backgrounds 

 of cages, houses, and the like, so as to give a less artificial appear- 

 ance to the surroundings. 



To my colleagues at Princeton I am under great obligations 

 for much valuable counsel and assistance. Professor Gilbert van 

 Ingen has prepared the maps and diagrams and Dr. W. J. Sinclair 

 has devoted much labour and care to the illustrations and has also 

 read the proofs. Both of these friends, as also Professors C. H. 

 Smyth and E. G. Conklin and Drs. Farr and McComas, have read 

 various parts of the manuscript and made many helpful sugges- 

 tions in dealing with the problems of treatment and presentation. 



