PROGKESSION ON THE LAND. 



57 



movement effects all this mechanically. When the limb has 

 swung forward as far as the inclination of the body at the 

 time will permit, it reverses pendulum fashion; the back 

 stroke of the pendulum actually placing the foot upon the 

 ground by a retrograde, descending movement. When the 

 right leg with which we commenced is extended and firmly 

 placed upon the ground, and the trunk has assumed a nearly 

 vertical position, the left leg is flexed, elevated, and the trunk 

 once more bent forward. The forward inclination of the 

 trunk necessitates the swinging forward of the left leg, which, 

 when it has reached the point permitted by the pendulum 

 movement, swings back again to the extent necessary to place 

 it securely upon the ground. These movements are repeated 

 at stated and regular intervals. The retrograde movement of 

 the limb is best seen in slow walking. In fast walking the 

 pendulum movement is somewhat interrupted from the limb 

 being made to touch the ground when it attains a vertical 

 position, and therefore before it has completed its oscillation.^ 

 The swinging forward of the body may be said to inaugurate 

 the movement of walking. The body is slightly bent and 

 inclined forwards at the beginning of each step. It is 

 straightened and raised towards the termination of thaTt act. 

 The movements of the body begin and terminate the steps, 

 and in this manner regulate them. The trunk rises vertically 

 at each step, the head describing a slight curve well seen in 

 the walking of birds. The foot on the ground (say the right 

 foot) elevates the trunk, particularly its right side, and the 

 weight of the trunk, particularly its left side, depresses the 

 left or swinging foot, and assists in placing it on the ground. 

 The trunk and limbs are active and passive by turns. In 

 walking, a spiral wave of motion, most marked in an antero- 

 posterior • direction (although also appearing laterally), runs 

 through the spine. This spiral spinal movement is observ- 

 able in the locomotion of all vertebrates. It is favoured in 

 man by the ahtero-posterior curves (cervical, dorsal, and lum- 

 bar) existing in the human vertebral column. In the effort 

 of walking the trunk and limbs oscillate on the ilio -femoral 



1 " In quick walking and running the swinging leg never passes beyond 

 the vertical which cuts the head of the femur." 

 4 



