MUSCLES IN RELATION TO POWER AND SPEED 



31 



impulses from behind, that the centre of gravity is most disjDlaced, and 

 tlie feet leave the ground to form new bases of support and re-establish 

 the disturbed equilibrium. This will be made obvious by examining 

 the various phases of movement in one or other of the several paces. 

 In the walk, which, as we have elsewhere pointed out, is one of four 

 time, the base of support is made to undergo a succession of changes 

 peculiar to it. In Plate II, figs. 1 and 6, it runs parallel with the 

 long axis of the body, 

 being formed by the two 

 left and right limbs re- 

 spectively. In fig. 2 it is 

 altered both in shajje and 

 extent by the right hind- 

 limb beintr brought to the 

 ground, thereby enlarging 

 its area, while at the same 

 time it is made to assume 

 a trians;ular form. In 

 fig. 5 the line of direc- 

 tion is diagonal from the 

 left fore to the right hind. 

 These alterations in the 

 base of support are called 

 forth by the forward in- 

 clination of the trunk dis- 

 placing the centre of gra- 

 vity. This forward dis- 

 placement is very much 

 more considerable as the 

 pace increases, as shown 



in particular phases of the fast gallop (figs. 3 and 4 of the same plate), 

 where a vertical line drawn from the centre of gravity would fall in front 

 of the fore-foot, or leading support, and consequently outside the base of 

 support, thus requiring a fresh base to be formed by the advancing fore- 

 liml) to re-establish equilibrium. 



I'lg. 19. — Base of Support 



MUSCLES IN RELATION TO POWER AND SPEED 



The movements of locomotion by which the body is transferred from 

 place to place ai-e effected by muscles, which, acting in obedience to the will, 

 are termed voluntary muscles. 



