464 



MOTION. 



Fig. 252. 



4567 



8 9 10 11 



12 U 14 



1 2 S 



Fig. 252 shows the simultaneous positions of both legs during a step, divided into four groups. The first group, 

 4 to 7, gives the different positions which the legs simultaneously assume white both are on the yruuml ; the 

 second group, H to 11, shows the various positions of both lays at the time when the posterior ley is elevated 

 from the ground, but behind the supported one; the third group, No. 12 to 14, shoii's the positions which the 

 legs assume when the swinging leg overtakes the standing one ; and the fourth group, 1 to 3, the positions 

 during the time i-jlien the swinging leg is propelled in advance of the resting one. 



plane of motion, whilst it moves forwards with sole, the hollow arch only excepted, is trough* 



,1 i r _ ~\T _ A _ -i ~ * 1. _ J I * .. . ' i ' il_ . I. _ _. _1 1 * K _ I. J ,. f 



the trunk, from No. 4 to 18, the distance from 

 the head of the femur to the foot must be con- 

 stantly increasing. To accomplish this the mus- 

 cles which extend the hip, knee, and ankle- 

 joints are gradually contracted, and the length 

 of the leg sufficiently increased by its extension 

 to reach from No. 18 to the ball of the foot 

 (Jig. 251). In these movements the sole of the 

 foot rotates on the ground, and (independently 

 of the angle formed by the legs) increases the 

 length of the step by the length of the foot 

 from the heel to the ball ; because, when the 

 head of the femur arrives at No, 18, fig. 251, 

 the line from the ankle-joint to the ball is 

 perpendicular to the ground. At the moment 

 that the head of the femur of the left leg arrives 

 at a position vertical to the foot, as No. 4, 

 fig. 251, the right leg is lifted from the 

 ground,* and, from its oblique position and 

 weight, swings forward like a pendulum, 

 whose axis of motion is in the hip-joint, Nos. 

 19 to 28, /?g.251, and having passed by the sup- 

 porting leg it touches the ground, with the 

 ankle-joint in advance of the head of the femur, 

 No. l,Jig- 251. The heel is first placed upon 

 the earth, and by degrees every part of the 



* Measure of the elevation of the heel and toes 

 in walking, the distance passed through 30 metres. 



into contact with the ground, and the head of 

 the femur is again over the ankle-joint, as before, 

 No. 4, fig. 251. The motion of the left leg al- 

 ternates with that of the right in the same 

 manner.* In the first period of the movement 

 the left leg is seen in the rear of the right leg, 

 No. 8 to ll,/?g. 252. Having overtaken the 

 latter, No. 12 to 14, fig. 252, it advances 

 before it and comes to the ground in sufficient 

 time to receive the weight of the body as soon 

 as the right leg ceases to act, No. 4, fig. 252, 

 so that the instant the weight of the trunk 

 is transferred to it from the right leg bend- 

 ing slightly and returning to its former posi- 

 tion, it acts like a spring, and prevents any 

 sudden concussion arising in consequence 

 of the translation of the burthen from one 

 leg to the other. The weight of the trunk 

 being thus propelled, supported, and transferred 

 from one leg to the other alternately, a constant 

 and uniform movement in a horizontal direction 

 is maintained. The right and left leg having 

 thus swung and supported the body alternately, 

 and having been on the ground simultaneously 

 a short, and separately a long, period, the ho- 

 rizontal path of the centre of gravity, during 

 these two movements, is equal to the length of 

 a double step. In consequence of this inter- 

 change of offices the supporting leg is active, 

 whilst the swinging leg is comparatively pas- 



* The Webers compare the action of the foot to the 

 rolling of a wheel, with this difference, that the ro- 

 tation of the wheel is uninterrupted, whilst that of 

 the foot is terminated and renewed at every step. 

 In walking on the ball of the foot, or on the toes, 

 the rotation is confined to the distance between the 

 ball of the foot and the point of the toes. 



