MOTION AND LOCOMOTION. 151 



Others passing before and behind the knee- joint keep it from 

 yielding; and so at the hip-joints: and 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 occipi- 

 tal 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 ad- 

 vanced limb supports the Body, and the foot in the rear at 

 the commencement of each step propels it. 



Suppose a man standing with his heels together to com- 

 mence 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 centre 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 goojd 

 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 sup- 

 port being thus widened from before back, a fall is prevented. 

 Meanwhile the right leg is kept straight, but inclines for- 

 wards above with the trunk when the latter advances, arid 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 knes being bent that limb swings forwards, 

 its foot just clearing the ground as the left did before. The 

 Body is meanwhile supported on the left foot alone, but when 

 the right completes its step the knee of that leg is straight- 

 ened and the foot thus placed, heel first, on the ground. 

 Meanwhile the left foot has been gradually leaving the 

 ground, and its toes only are at that moment upon it: from 

 these a push is given, as before, with the right foot, and the 



