Xli PREFACE 



roof-bones of the vault of the skull but in some types of primitive fish 

 to have already entered the regressive phase of its ancestral history at 

 the time when the dermal bones of the skull had first completely covered 

 over the brain and formed a protective investment for the principal 

 sense-organs, namely the olfactory, visual, and static. 



The authors hope that the book will be of interest to readers outside 

 as well as within the medical profession and that it will stimulate the 

 study of other organs and systems of the human body from the stand- 

 point of comparative anatomy, in addition to the purely practical aspect. 

 We feel assured that the wider outlook which is gained by the investigation 

 of any particular structure by the embryological and comparative methods 

 well repays the additional time which is spent in acquiring this know- 

 ledge. It not only greatly increases interest in the particular organ which 

 is being studied but it also gives a better insight into the special functions 

 of the system both in health and disease. 



Special care has been taken in selecting and making the illustrations, 

 each of which has an independent explanatory legend. They have been 

 assembled from various sources ; some are original drawings made 

 specially for this work or which have previously been published by either 

 one or both of us in the British Journal of Surgery, the Journal of Anatomy, 

 or the Medical Press and Circular. Others have been reproduced from 

 blocks, redrawn from lithographic plates, photographs, or drawings 

 illustrating original papers, or from well-known standard works. The 

 source of the latter has in each case been duly acknowledged, and the 

 authors desire to take this opportunity of expressing their gratitude to 

 the publishers and authors who have generously allowed us to make use 

 of these figures ; and we desire specially to thank the publishers of those 

 journals and books from which certain of the illustrations have been 

 reproduced : John Wright and Sons, Bristol ; Bailliere, Tindall and 

 Cox, London ; Quarterly Journal of the Microscopical Society, London ; 

 Cambridge University Press ; Macmillan and Co., London ; Contribu- 

 tions to Embryology, John Hopkins University. 



The authors also wish to acknowledge their indebtedness to the 

 published works of all those writers whose names appear in the biblio- 

 graphy and in the following list. These works have been of the greatest 

 value in determining the general trend of the book and an aid in coming 

 to the conclusions which we have been enabled to draw from our own 

 observations and experience. We wish especially to mention the names 

 of the following authors : Achucarro, Agduhr, Ahlborn, Altmann, Amprino, 

 Bailey, Badouin, de Beer, Beraneck, Berblinger, Bernard, Bertkau, 

 Bourne, Brown, Cairns, Cajal, Calvet, Cambridge Natural History, 



