PREFACE. 



In the present volume I have endeavoured to explain, 

 in simple language, some difficult problems in " Animal 

 Mechanics." In order to avoid elaborate descriptions, I 

 have introduced a large number of original Drawings 

 and Diagrams, copied for the most part from my Papers 

 and Memoirs " On Flight," and other forms of " Animal 

 Progression." I have drawn from the same sources 

 many of the facts to be found in the present work. My 

 best thanks are due to Mr. W. Ballingall, of Edinburgh, 

 for the highly artistic and effective manner in which he 

 has engraved the several subjects; . The figures, I am 

 happy to state, have in no w^ay deteriorated in his 

 hands. " * ^ ' -' "'^ 



KoYAL College of Surgeons of Edinburgh, 

 July 1873. 



