MOTION AND LOCOMOTION 109 



the heel to the thigh, and from the dorsum of the foot to 

 the shin-bone (tibia). Others passing before and behind the 

 knee-joint keep it from yielding; and so at the hip-joints: the 

 others again, lying in the walls of the abdomen and along the 

 vertebral column, keep the latter rigid and erect on the pelvis; 

 and finally the skull is kept in position by muscles passing from 

 the sternum and vertebral column to it, in front of and behind 

 the occipital condyles. 



Locomotion includes all the motions of the whole Body in 

 space, dependent on its own muscular efforts: such as walking, 

 running, leaping, and swimming. 



Walking. In walking the Body never entirely quits the 

 ground, the heel of the advanced foot touching the ground in 

 each step before the toe of the rear foot leaves it. The advanced 

 limb supports the Body, and the foot in the rear at the com- 

 mencement of each step propels it. 



Suppose a man standing with his heels together to commence 

 to walk, stepping out with the left foot ; the whole Body is at first 

 inclined forwards, the movement taking place mainly at the 

 ankle-joints. By this means the center of gravity would be 

 thrown in front of the base formed by the feet and a fall on the 

 face result, were not simultaneously the left foot slightly raised 

 by bending the knee and then swung forwards, the toes just clear 

 of the ground and, in good walking, the sole nearly parallel to it. 

 When the step is completed the left knee is straightened and the 

 sole placed on the ground, the heel touching it first, and the base 

 of support being thus widened from before back, a fall is pre- 

 vented. Meanwhile the right leg is kept straight, but inclines 

 forwards above with the trunk when the latter advances, and as 

 this occurs the sole gradually leaves the ground, commencing 

 with the heel. When the step of the left leg is completed the 

 great toe of the right alone is in contact with the support. With 

 this a push is given which sends the trunk on over the left leg, 

 which is now kept rigid, except at the ankle-joint; and the right 

 knee being bent that limb swings forwards, its foot just clearing 

 the ground as the left did before. The Body is meanwhile sup- 

 ported on the left foot alone, but when the right completes its 

 step the knee of that leg is straightened and the foot thus placed, 

 heel first, on the ground. Meanwhile the left foot has been gradu- 



