It is a unique pleasure to express my indebtedness to the Upper Palæolithic artists of the now extinct Crô-Magnon race, from whose work I have sought to portray so far as possible the mammalian and human life of the Old Stone Age. While we owe the discovery and early interpretation of this art to a generation of archæologists, it has remained for the Abbé Breuil not only to reproduce the art with remarkable fidelity but to firmly establish a chronology of the stages of art development. These results are brilliantly set forth in a superb series of volumes published by the _Institut de Paléontologie humaine_ on the foundation of the Prince of Monaco; in fact, the memoirs on the art and industry of _Grimaldi_, _Font-de-Gaume_, _Altamira_, _La Pasiega_, and the Cantabrian caves of Spain (_Les Cavernes de la Région Cantabrique_), representing the combined labors of Capitan, Cartailhac, Verneau, Boule, Obermaier, and Breuil, mark a new epoch in the prehistory of man in Europe. There never has been a more fortunate union of genius, opportunity, and princely support. In the collection of materials and illustrations from the vast number of original papers and memoirs consulted in the preparation of this volume, as well as in the verification of the text and proofs, I have been constantly aided by one of my research assistants, Miss Christina D. Matthew, who has greatly facilitated the work. I am indebted also to Miss Mabel R. Percy for the preparation and final revision of the manuscript. From the bibliography prepared by Miss Jannette M. Lucas, the reader may find the original authority for every statement which does not rest on my own observation or reflection. Interest in human evolution centres chiefly in the skull and in the brain. The slope of the forehead and the other angles, which are so important in forming an estimate of the brain capacity, may be directly compared throughout this volume, because the profile or side view of every skull figured is placed in exactly the same relative position, namely, on the lines established by the anatomists of the Frankfort Convention to conform to the natural pose of the head on the living body.