PREFACE 15 



originally taken were inaccessible to me at the time when I 

 was completing the list of illustrations. I am therefore in- 

 debted to Professor Osborn and the Macmillan Company for 

 the opportunity of copying the reproductions of these two 

 illustrations from Evolution of Mammalian Molar Teeth. It 

 will be observed that the mandibular molar in Fig. 15 was 

 redrawn for Professor Osborn 's work; this accounts for the 

 differences in nomenclature from the original figure. For 

 the specimens from which Figs. 56A and C were made I am 

 indebted to Dr. M. J. Cramer and Mr. B. H. Broadbent respec- 

 tively. Professor Keith has kindly allowed me to reproduce 

 from his works Figs. 59 and 98. I have the opportunity to 

 include Fig. 84 through the courtesy of Oldfield Thomas, Esq. 

 Fig. 87 is copied from Dr. Otto Walkhoff's monograph Der 

 Unterkiefer der Antkropomorphen und des Menschen in the late 

 Professor Selenka's series Studien ilber Entwickelungsgeschichte 

 der Tiere, heft 9. 



I have enjoyed the assistance of several of the departmental 

 staff in the preparation of this work. Mr. 0. P. Leonhart has 

 prepared a number of the specimens many of which have been 

 photographed by Miss Alice Thing. The index is largely the 

 work of Miss W. Eothenbecker. I am under special personal 

 obligation also to my secretary Mrs. K. W. Merrell for many 

 suggestions made in the course of writing the manuscript as 

 well as for the technical preparation of the sheets for the 

 press. 



T. Wingate Todd. 



Cleveland, Ohio, 

 Dec. 1, 1917. 



The transformation of the United States into an armed camp, 

 heartening and inspiring to all who have been privileged to 

 live in the midst of it, has been responsible for unforeseen 

 delay in the publication of this volume. One after another 

 those by whose joint labor the book should have been produced 

 months ago have taken up other duties in the cause for free- 



