vi PREFACE. 



I am under great obligations to many friends who have kindly rendered me their 

 aid. Professor George A. Piersol has given me much valuable information and 

 allowed me the unstinted use of his anatomical material ; Dr. Astley P. C. Ashhurst 

 made many of the dissections and aided in correcting and preparing the manuscript 

 for the press ; Dr. Frank D. Dickson did most of the proof-reading and prepared the 

 index ; Dr. T. Turner Thomas made many of the earlier preparations ; and Dr. Henry 

 Beates aided in the revision of the first portion of the manuscript. To these and 

 others who have contributed to the formation of the book I desire to express my 

 thanks. 



To the hearty cooperation and unfailing generosity of my publishers is due the 

 presentation of such an attractive volume. I asked them for nearly everything I 

 could think of, and they gave me nearly everything I asked for. 



In conclusion : this work is recognized as being far from complete, but it is 

 intended to be suggestive rather than absolute. It is not designed so much to 

 present facts as to furnish reasons, and it is hoped that it will appeal to the practising 

 physician and surgeon as well as to the student. 



GWILYM G. DAVIS. 

 PHILADELPHIA, August, 1910. 



