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 of 

 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 most 

 varied results attained, without the least departure from the 

 general plan which has been adopted in the construction of 

 the various species of the same group ; and this solely by 

 slight changes in the forms and proportions of some of the 

 instruments whose union makes-up the entire body. The 

 organs of locomotion in the Mammalia furnish us with 

 obvious examples of this principle. This class includes not 

 only the quadrupeds which run or bound along the surface of 

 the ground, but animals which are destined to live solely in 

 water like fishes, others which sometimes swim through that 

 element and sometimes inhabit the land, others which 

 possess wings that enable them to fly through the air like 

 birds, and others which only employ their anterior members 

 for grasping or feeling ; yet in all these animals, these organs 

 are constructed of the same parts. In the paddles of a Seal 



