THE MUSCLES 19 



We have been speaking so far only of the swinging limb ; 

 we have seen that during that movement all its muscle- 

 engines — some fifty-four in number — are set in motion, 

 but so far we have said nothing of what the corresponding 

 engines in the stationary or supporting limb were doing 

 when the swinging limb was passing forward. As a 

 matter of fact they were thrown into action and were 

 performing a very skilful acrobatic feat. If I were to 

 poise a man's body on the end of a billiard cue and 

 maintain it balanced so for some time, you would look 

 upon me as a wonderful acrobat. And yet if the walking 

 figure of the man shown in Plates I. and II. be examined, 

 it will be seen that a feat of this kind is being carried out 

 with every step. In that figure the right leg is shown as 

 the stationary or supporting member ; the left as the one 

 which swings forward. The whole weight of the man's 

 body is supported on the round, slippery, and ball-shaped 

 head of the right thigh bone ; it is balanced there by all 

 the muscles which surround the hip-joint, some fifteen in 

 number, being set into motion and working against each 

 other. The socket of the hip bone or pelvis in which the 

 head of the thigh bone is pivoted is equally smooth and 

 slippery. As the swinging limb is flung forward under 

 its proper engines, the centre of gravity of the body has 

 to be poised vertically over the head of the thigh bone of 

 the stationary limb and kept thus balanced by muscles 

 which pass up from the thigh bone to act on the hip bone 

 or pelvis. The hip bone serves as the crank on which 

 the balancing muscle-engines act. The least bit the 

 body sways off" the plumb, this way or that, then at that 

 moment the right muscles are set in more vigorous action 

 to meet the emergency and bring the body back to the 

 straight. All the time, too, that the free limb is swinging 

 forward, the centre of gravity of the body is also being 

 advanced, hence the balancing muscles of the stationary 

 limb have to meet that change by varying the rate of 

 their action. 



We have been thinking only about the muscles of the 

 stationary limb which balance the trunk on the top of the 



