738 



PHYSIOLOGY OF THE DOMESTIC ANIMALS.. 



muscular exertion is required in walking on level ground. In ascending 

 an incline, however, the active limb has at each step to elevate the weight 

 of the body by extending the knee- and ankle-joint by the thigh-exten- 

 sors and calf-muscles, therefore greatly increasing the muscular power 

 required. During walking the trunk leans toward the active leg, owing 

 to the contraction of the glutei muscles and the tensor fascia lata, and is 

 inclined slightly forward to overcome the resistance of the air. The 

 more anteriorly the trunk is advanced the more the centre of gravity of 

 the body tends to lie in the line of the active leg, and, consequently, the 

 stronger is the forward propulsion of the body. Hence, in rapid walk- 

 ing the body is more bent forward than in slow walking. During the 

 advancing of the passive leg the trunk rotates on the head of the active 

 femur and is compensated by the arm of the side of the oscillating leg 



FIG. 300. THE DIFFERENT POSITIONS OF THE LEGS OF MAN IN WALKING, 



AFTER WEBEK. 



A, the propelling le ; B, the " pendulum " leg. 



swinging in the opposite direction, while that on the other side swings 

 in the same direction as the oscillating leg. 



Running is distinguished from walking by the fact that at a certain 

 moment the body is raised in the air, neither leg touching the ground. 

 In walking, on the other hand, both feet rest on the ground for the 

 greater part of the step. In running the active leg, as it is forcibly ex- 

 tended from a flexed position, gives the body the necessary impetus, the 

 active leg leaving the ground before the swinging foot has reached the 

 ground. There is thus an interval during which both feet are off the 

 ground, and as each foot comes to the ground it executes a new swing 

 without waiting for the pendulous swing which occurs in walking. 



In jumping the propulsion of the bod}' takes place from both feet 



