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 way deteriorated in his hands. ROYAL COLLEGE OF SURGEONS OF EDINBURGH, July 1873. CONTENTS. PAGE Motion associated with the life and well-being of animals, Motion not confined to the animal kingdom; all matter in Flight a more unstable movement than that of walking and The earth, the water, and the air furnish the fulcra for the levers formed by the travelling surfaces of animals, The body and wing reciprocate in flight; the body rising when the wing is falling, and vice versâ, stronger than terrestrial ones, Fins, flippers, and wings form mobile helics or screws, Artificial fins, flippers, and wings adapted for navigating the 12 The legs move by the force of gravity. Resistance of fluids. Ligaments. Effects of atmospheric pressure on limbs. Active organs of locomotion. Muscles; their properties, arrange- ment, modes of action, etc., Muscular cycles. Centripetal and centrifugal movements of Muscles arranged in longitu- Muscles take precedence of bones in animal movements, Oblique spiral muscles necessary for spiral bones and joints, The spiral movements of the spine transferred to the extremi- The travelling surfaces of animals variously modified and |