ii MECHANICS OF LOCOMOTOB APPAEATUS 121 



whole sole of the foot, but later, as the heel rises, on the point of the 

 foot only. In the first half of the step owing to the extension 

 of the right knee there is an upward vertical oscillation of the 

 hip, shoulder, and head ; while in the second half of the step there 

 is a downward movement owing to forward flexion of the right 

 ankle, and partly also of the knee on the same side. So that at 

 each step there is a double vertical oscillation of the hip, shoulder, 

 and head, as clearly shown by the figure. According to the Webers 

 these vertical oscillations attain a height of 32 mm., according to 

 Car let of 37 mm., in persons of average height, during fairly rapid 

 walking ; they increase in proportion to the length of the steps. 



Besides these vertical oscillations, the top of the head and the 

 shoulders and hips show lateral horizontal oscillations during 

 walking, which are very apparent on looking down from a height, 

 for instance from a window, upon a person walking in the street. 

 While the vertical oscillations coincide with the length of a step, 

 the horizontal oscillations correspond to the double steps or a whole 

 step cycle. These lateral horizontal oscillations reach their maximum 

 at the same moment as the vertical oscillations. In the diagram 

 of Fig. 80 the maximal lateral oscillation therefore falls to the 

 right at the 5th phase, and the maximum of lateral oscillation to 

 the left at the 15th phase. The further apart the limbs are in 

 walking, the more pronounced are these lateral oscillations, which 

 evidently depend upon the degree of abduction at which the feet 

 are planted upon the ground. 



The oscillations of the shoulders and hips round a vertical axis 

 should also be noted ; these accompany the lateral oscillations of 

 the trunk. At each step the leg that is moving forward is accom- 

 panied by a forward movement of the hips and a backward move- 

 ment of the shoulders, i.e. a slight twist of the trunk round a 

 vertical axis. This torsion may be so exaggerated as to become 

 very apparent, but it is present to a slight extent even in normal 

 walking, especially in women with a large pelvis. The forward 

 movement of the hips is also due to the swing forward of the 

 lower limb of the corresponding side and the active contraction of 

 the lumbar muscles ; the backward inclination of the shoulders is 

 produced by the swing forward of the upper limb of the opposite 

 side, which, according to Duchenne, is not purely passive, as it 

 depends partly on contraction of the deltoid muscle. Fig. 80 shows 

 plainly that while the left leg swings forwards, the right arm 

 becomes more and more flexed at the elbow, and is raised and 

 advanced. This torsion of the trunk and active oscillation of the 

 upper limbs, which balance the body, increase in rapid walking. 



These simultaneous and opposite movements of the upper and 

 lower limbs in the ordinary gait of man correspond with the 

 alternate movement of the four limbs in the ordinary gait of the 

 quadrupeds. 



