464 
MOTION. 
Fig. 252. 
6&9 1011 
12 13 14 igs 
Fig. 252 shows the simultaneous positions of both legs during a step, dinided into four groups. 
4 to 7, gives the different positions which the legs simultaneously assume while both are on the ground ; 
second group, 8 to 11, shows the various positions of both legs at the time when the posterior p 
From the ground, but behind the supported one ; the third group, No. 12 to 14, shows the positions which 
legs assume when the swinging leg overtakes the standing one ; and the fourth group, 1 to 3, the p 
during the time when the swinging leg is propelled in advance of the resting one, 
plane of motion, whilst it moves forwards with 
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 
(fig. 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, 
Sig. 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, fig.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. 1, fig. 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. 
Num- Elevation | Elevation 
ber of of the [of the point 
steps. | Time. heel. jof the toe.| Velocity. 
metre. metre. 
41 17.4 0.178 0.092 1.72 
39 12”.7 0.173 0.115 2.36 
The first g 
d 
4 
ry 
e 
leg is elevated 
~ 
sole, the hollow arch only excepted, is brou 
into contact with the ground, and the head ¢ 
the femur is again over the ankle-joint, as before, 
No. 4, fig. 251. The motion of the left leg ak 
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 11, fig. 252. Having overtaken the 
latter, No. 12 to 14, fig. 252, it advances 
before it and comes to the ground in suffiel 
time to receive the weight of the body as s 
as the right leg ceases to act, No. 4, fig. 
so that the instant the weight of the tra 
is transferred to it from the right leg bem 
ing slightly and returning to its former posi 
tion, it acts like a spring, and prevents an 
sudden concussion arising in consequene 
of the translation of the burthen from on 
leg to the other. The weight of the tran 
being thus propelled, supported, and transfern 
from one leg to the other alternately, a consta 
and uniform movement in a horizontal dire 
is maintained. The right and left leg 
thus swung and supported the body altern 
and having been on the ground simulta 
a short, and separately a long, period, the h 
rizontal path of the centre of gravity, dur 
these two movements, is equal to the length 
a double step. In consequence of this mite 
change of offices the supporting leg is act 
whilst the swinging leg is comparatively f 
ae 
<-> 
* The Webers compare the action of the foot 
rolling of a wheel, with this difference, that 
tation of the wheel is uninterrupted, whi 
the foot is terminated and renewed at ev 
In walking on the ball of the foot, or on t 
the rotation is confined to the distance be 
ball of the foot and the point of the toes. 
we 
