PREFACE TO THE THIRD EDITION 



THE rapid exhaustion of the second edition of this text has hastened 

 the appearance of the present volume. Its contents have again been sub- 

 jected to a systematic revision which affects each chapter more or less pro- 

 foundly. The addition of much new material and the recasting and 

 modifying of former descriptions will result, it is hoped, in a two-fold gain, 

 without appreciably increasing the size of the book. 



L. B. A. 



CHICAGO, ILL., 

 August, 1920. 



PREFACE TO THE SECOND EDITION 



THE untimely death of Professor Prentiss has made necessary the transfer 

 of his 'Embryology' into other hands. In this second edition, however, the 

 general plan and scope of the book remain unchanged although the actual descrip- 

 tions have been extensively recast, rewritten, and rearranged. A new chapter 

 on the Morphogenesis of the Skeleton and Muscles covers briefly a subject not 

 included hitherto, ^orty illustrations replace or supplement certain of those 

 in the former edition. 



In preparing the present manuscript a definite attempt has been made to 

 render the descriptions as clear and consistent as is compatible with brevity and 

 accuracy. It has likewise been essayed to evaluate properly the embryological 

 contributions of recent years, and, by incorporating the fundamental advances, 

 to indicate the trend of modern tendencies. Since no page remains in its entirety 

 as originally penned by Professor Prentiss, the reviser must assume full respon- 

 sibility for the subject-matter as it now stands. 



It is hoped that those who read this text will co-operate with the writer by 

 freely offering criticisms and suggestions. 



L. B. A. 

 iii 



