TERRESTRIAL MOTION (mAn). 



Ill 



as the most important representative of the method of walking 

 adopted by quadrupeds. As to other animals, they will be 

 studied in an accessory manner, and especially with reference 

 to the resemblances and differences which the modes of their 

 locomotion present when compared with the types which we 

 have chosen. 



Many authors have already treated on this subject ; from 

 the time of Borelli to that of modern physiologists, science 

 has slowly advanced : it seems to us that it can now resolve 

 all obscure questions, and determine them definitely, by the 

 employment of the graphic method. 



While observation employed alone furnishes only incom- 

 plete and sometimes false data, the graphic method carries its 

 precision into the analysis of the very complex movements 

 concerned in locomotion. We shall see, when we treat of the 

 paces of the horse, that the disagreement we find among 

 writers on this subject shows clearly the insufficiency of the 

 methods hitherto employed. 



Human locomotion, though much more simple in its mechan- 

 ism, is still very difficult to analyse ; the works of the two 

 Webers, though considered as the deepest investigation of 

 human locomotion that have yet been made, show many 

 omissions and some errors. 



The most simple and usual pace is walking, which, according 

 to the received definition, consists in that mode of locomotion 

 in which the body never quits the ground. In running and 

 leaping, on the contrary, we shall see that the body is en- 

 tirely raised above the ground, and remains suspended during 

 a certain time. 



In walking, the weight of the body passes alternately from 

 one leg to the other, and as each of these limbs places itself 

 in turn before the other, the body is thus continually carried 

 forward. This action appears very simple at first sight, but 

 its complexity is soon observed when we seek to ascertain 

 what are the movements which concur in producing this 

 motion. 



We see, in fact, that each movement of the limbs brings 

 under consideration a phase of impact and one of support in 

 each of Ihese ; the different articulations bend and extend 



