NOTE ON THE ILLUSTRATIONS 
The original drawings, made especially for this book, 
are by Charles R. Knight and James M. Gleeson, 
under the direction of Mr. Knight.. The fact that the 
originals of these drawings have been presented to and 
accepted by the United States National Museum is 
evidence of their scientific value. Mr. Knight has 
been commissioned by the Smithsonian Institution, the 
United States National Museum, and the New York 
Museum of Natural History, to do their most im- 
portant pictures of extinct animals. He is the one 
modern artist who can picture prehistoric animals 
with artistic charm of presentation as well as with full 
scientific accuracy. In this instance, the author has 
personally superintended the artist’s work, so that it is 
as correct in every respect as present knowledge makes 
possible. Of the minor illustrations, some are by Mr. 
Bruce Horsfall, an artist attached to the staff of the 
New York Museum of Natural History, and all have 
been drawn with the help of and under the author’s 
supervision. 
