494 ACT OF WALKING :—OTHER MODES OF LOCOMOTION. 
elongation acts through the thigh upon the pelvis, and thus 
carries forward the whole body. At the same time, the pelvis 
makes a slight turn upon the femur of the other side on 
which it is resting ; and the limb which was at first behind 
the other, is now drawn forward by a flexion of its joints, 
and is planted on the ground in front of the other, so as to 
serve for the support of the body in its turn; whilst the 
other, by extending itself, gives a fresh forward impulse to 
the body. Thus each limb is alternately made to support the 
whole weight of the body, just as it would do in standing on 
one leg; while at the same time the other is engaged in 
urging it forwards. Hence the centre of gravity must vibrate 
a little from side to side in the act of walking, so that it may 
be brought alternately over each foot ; and this movement 
from side to side is the more obvious, in proportion as the 
pelvis is wider, and the limbs more separated from each other. 
Hence it is more seen in women than in men, on account 
the greater proportional breadth of the hips in the former. 
658. In all the higher animals, as in Man, there are 
members which serve for locomotion ; but the nature of these 
movements varies greatly ; and there is a corresponding differ- 
ence in the structure of the instruments by which they are 
performed. The manner in which the Creator has made the 
same organs answer a variety of different purposes, in accord- 
ance with the habits of the animals to which they belong, is 
a most interesting object of study ; for we see the m 
varied results attained, without the least departure from th 
general plan which has been adopted in the construction o 
the various species of the same group; and this solely b 
slight changes in the forms and proportions of some of th 
instruments whose union makes-up the entire body. Th 
organs of locomotion in the Mammalia furnish us wi 
- obvious examples of this principle. This class includes n 
only the quadrupeds which run or bound along the surface o: 
the ground,—but animals which are destined to live solely i 
water like fishes,—others which sometimes swim through tha: 
element and sometimes inhabit the land,— others whi 
possess wings that enable them to fly through the air lik 
birds,—and others which only employ their anterior membe 
for grasping or feeling ; yet in all these animals, these orga 
are constructed of the same parts. In the paddles of a S 
