OF LOCOMOTION. 107 



scribed hy the space comprised between the two feet. Here a 

 slight force is sufficient to destroy the equilibrium, and it is only 

 by enlarging the base of support in one direction more than in 

 another that a fall can be prevented. 



The movements by which we regain the perpendicular in the 

 i*ase of support are in a measure automatic. Thus, to resist A 

 force tending to make us fall forward the foot is rapidly advanced : 

 if the body leans to the left we suddenly extend the right arm to 

 re-establish the equilibrium, if a force tends to throw us backward, 

 we put a foot behind and throw the body in advance. The man 

 who has a large belly and the man bearing a heavy load upon 

 his shoulders are both obliged to assume attitudes that change the 

 position of the centre of gravity. The first carries the body back- 

 wards in order that the vertical line passing through this point 

 may alsj fall between the two feet, and for the same reason, the 

 second bends the body forward. A woman who carries an infant 

 upon her right arm inclines the body to the left side: thus, we 

 are constantly resorting to mechanics, even without possessing the 

 most elementary notions of the science, and the most certain 

 causes of our preservation are found in the continual application 

 of physical laws, of which our reason has not the knowledge. 



When an animal rests upon its four members at the same time, 

 his standing is more firm, more solid and less fatiguing: for the 

 base of support is then very large. Then, without inconvenience 

 the feet may be much smaller than in the bipeds and consequently 

 lighter. 



OF LOCOMOTION. 



85. The objects of the motions which we perform is either to 

 change the position of certain parts of the body, or to transport 

 us from one place to another. 



86 The faculty of changing place is called locomotion. 



87. The movements of progression by the help of which man 

 and animals change place, are produced by certain parts of the 

 Dody which being flexed, rest upon a resisting object, and being 

 again immediately extended, push forward the rest of the body. 



88. In man the organs of locomotion are the abdominal mem- 

 bers, or lower extremities; in quadrupeds the thoracic as well 

 as the abdominal members ; and in birds that fly, the wings. 



89. In walking, the body of man is moved alternately by onw 



85. What is the object of the motions which we perform ? 



bG. What is meant by locomotion? 



87. How is progression effected? .^w* 



88 What are the organs of locomotion ? 



ti'.i How is walking distinguished from running and leaping' OF THE 



OF 



