PROGRESSION ON THE LAND. 



59 



of the feet and limbs upon the trunk, generate a forward 

 wav^e movement, accompanied by a certain amount of vertical 

 undulation. The diagonal movements of the trunk and 

 extremities are accompanied by a certain degree of lateral 

 curvature ; the right leg and left arm, when they advance to 

 make a step, each describing a curve, the convexity of which 

 is directed to the right and left respectively. Similar curves 

 are described by the left leg and right arm in making the 

 second or complementary step- When the curves formed by 

 the right and left legs or the right and left arms are joined, 

 they form waved tracks symmetrically arranged on either 

 side of a given line. The curves formed by the legs and 



4 5 67 8 910 11 12 13 11 12 3 



¥ia. 27 shows the simultaneous positions of both legs during a step, divided 

 into four groups. The first group (A), 4 to 7, gives the different positions 

 which the legs simultaneously assume while both are on the ground ; the 

 second group (5), 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; the 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 swing- 

 ing leg is propelled in advance of the resting one. The letters «, b, and c 

 indicate the angles formed by the bones of the right leg when engaged in 

 making a step. The letters w, n, and o, the positions assumed by the right 

 foot when the trunk is rolling over it. g Shows the rotating forward of the 

 trunk ui)on the left foot (/) as an axis, h Shows the rotating forward of 

 the left leg and foot upon the trunk (a) as an axis. Compare with fig. 4, 

 p. 21 ; with fig. 24, p. 47 ; and with fig. 26, p. 55.— After Weber. 



aims intersect at every step, as shown at fig. 19, p. 39. 

 Similar curves are formed by the quadruped when walking 



