BOOK THE SECOND. 



FUNCTIONS : TERRESTRIAL LOCOMOTION. 



CHAPTER I. 



OF LOCOMOTION IN GENERAL. 



Conditions common to all kinds of locomotion Borelli's comparison- 

 Hypothesis of the reaction of the ground Classification of the modes 

 of locomotion, according to the nature of the point of resistance, in 

 terrestrial, aquatic, and aerial locomotion Of the partition of muscular 

 force between the point of resistance and the mass of the body Pro- 

 duction of useless work when the point of n Stance is movable. 



THE most striking manifestation of movement in the dif- 

 ferent species of animals is assuredly locomotion : the act by 

 which each living creature, according to its adaptation to out- 

 ward circumstances, moves on the earth, in the water, or 

 through the air. Therefore it is more convenient to study 

 movement with regard to locomotion, for we can thus observe 

 it under the most varied types. 



At the commencement of these studies we ought to consider 

 the general characteristics of the function which is to occupy 

 attention, and to point out the general laws which are to be 

 found in all the modes of animal locomotion. But what can 

 bo more difficult than to ascertain the common features which 

 unite acts so different as those of flying and of creeping, as 

 the gallop of a horse and the .swimming of a fish? Still this 

 lias been frequently attempted. liorelli has endeavoured to 

 represent the various modes of terrestrial locomotion, by the 

 different methods which a boatman employs to direct his boat. 



This comparison may, with some additional developments, 

 serve to e.xplain the mechanism of the piincipal types of loco- 

 motion. 



