Based on the work of Samuel Wendell Williston and Dr. W. K. Gregory, author and editor of the original title published in 1925, this volume consists of two major portions -- a structure-by-structure account of the reptile skeleton, followed by a classification of the various reptile groups based on osteological characters. It was designed to give in outline form an account of the nature of the skeletal system of numerous reptile types living and extinct.