WALKING. 445 



LOCOMOTIVE MOVEMENTS. 1 



a. Walking. 



Walking is motion on a fixed surface, the centre of gravity being 

 alternately moved by one of the extremities and sustained by the other, 

 without the latter being, at any time, completely off the ground. It 

 consists of a succession of steps, which are effected in the erect atti- 

 tude and on a horizontal surface by bending one of the thighs upon 

 the pelvis and the leg upon the thigh, so as to detach the foot from the 

 ground by the general decurtation of the limb. The flexion of the 

 limb is succeeded by its being carried forward ; the heel is then brought 

 to the ground, and, successively, the whole of the inferior surface of 

 the foot. If the bones of the leg were perpendicular to the part which 

 first touches the ground, we should 

 experience a jolt ; but, instead of that, Fi g- 193 - 



the foot descends in an arc of a circle, 

 the centre of which is the point of the 

 heel. 



In order that the limb shall be thus 

 carried forward, the pelvis must have 

 described a movement of rotation on 

 the head of the thigh-bone of the 

 limb that has not been moved, and 

 must have carried forward the cor- Movement of the Foot in Walking, 

 responding side of the body. As yet, 



only one limb has advanced. The base of sustentation has been modi- 

 fied, but there has been no progression. The limb, remaining behind, 

 has now to be raised and brought forward, so as to pass the other, or to 

 be on the same line with it, as the case may be; and this finishes the 

 step. In order to bring up the limb that is behind, the foot must be 

 successively detached from the soil, from the heel to the toe. In this 

 way, an elongation of the limb is produced, which assists in advancing 

 the corresponding side of the trunk, and excites the rotation of the 

 pelvis on the head of the thigh-bone first carried forward. A succes- 

 sion of these movements constitutes walking; the essence of which con- 

 sists in the heads of the thigh-bones forming fixed points, on which the 

 pelvis turns alternately, as upon a pivot, describing arcs of circles, 

 which are more extensive in proportion to the size of the steps. 



Walking in a straight line requires that the arcs of circles described 

 by the pelvis, and the extension of the limbs when carried forward, 

 shall be equal; otherwise, the body will be directed towards the side 

 opposite to that of the limb whose movements are more extensive. 

 Without the aid of vision, it would be impracticable for us to make the 

 arcs equal, or to walk straight forward. 



Walking backwards differs somewhat from this. The step is com- 



1 On the whole subject of Animal Motion, Animal Dynamics, Locomotion, or Progressive 

 Motion of Animals, see an elaborate article by J. Bishop, in Cyclopaedia of Anatomy and 

 Physiology, Part xxiii. p. 407, London, April, 1842, and Prof. E. Weber, Art. Muskelbewe- 

 gung, in Wagner's Handworterbuch der Physiologic, I5te Lieferung, s. 1, Braunschweig, 

 1846. 



