LOCOMOTION, 657 
joints somewhat, which would also favor falling backward 
(bending of the knees). 4. The line of gravity of the whole 
body passes in front of a line joining the two ankle-joints, so 
that the body would tend, but for the contraction of the mus- 
cles of the calves of the legs, to fall forward. 
Taking these different facts into consideration explains the 
various directions in which an individual, when erect, may fall 
according as one or the other line (center) of gravity is dis- 
placed for a long enough time. 
Walking (man) implies the alternate movement of each leg 
forward, pendulum-like, so that for a moment the entire body 
4567 891011 121314 123 
Fig. 492.—Shows the simultaneous positions of both legs during a step, divided into four 
oo (after Weber). First group (4), 4 to 7, gives the different positions which the legs 
simultaneously assume while both are on the ground ; second group (B), 8 to 11, shows 
the various positions of both legs at the time when the posterior leg is elevated from the 
ground, but behind the supported one; third group (C), 12 to 14, shows the positions 
which the legs assume when the swinging leg overtakes the standing one ; and the fourth 
group (D), 1 to 3, the positions during the time when the swinging leg is propelled in 
advance of the resting one. The letters a, b, and ¢ indicate the angles formed by the 
bones of the right leg when engaged in making a step; the letters m, 1, and o, the posi- 
tions assumed by the right foot when the trunk is rolling over it; g, shows the rotating 
forward of the trunk upon the left foot (/) as an axis; h, shows the rotating forward of 
the left leg and foot upon the trunk (a) as an axis. 
ae (en 
-— a 
pevnaine ee E 
@ 
Fic. 493.—Overhand swimming (Pettigrew). 
must be supported on one foot. When the right foot is lifted 
or swung forward, the left must support the weight of the 
42 d 
