MAMMIFEROUS QUADRUPEDS. 433 



upon the limbs, possess great range of motion, and 

 can traverse with fewer steps a given space. 



The office of the limbs, as far as they are con- 

 cerned in progressive motion, is two-fold. They 

 have, first, to sustain the weight of the body, whicli 

 they must do by acting in opposition to the force of 

 gravity; and they must, secondly, give the body 

 an impulse forwards. Let us consider more par- 

 ticularly the relations which the structures bear to 

 each of these two functions. 



The limbs of quadrupeds constitute four columns 

 of support to the trunk, which is placed horizon- 

 tally above them ; but the whole weight of the 

 body, together with that of the head and neck, 

 does not bear equally upon them ; the fore extre- 

 mities almost always sustain the greater part of 

 that weight, both because the fore part of the 

 trunk is itself heavier than the hind part, and be- 

 cause it is loaded with the additional weight of the 

 head and neck. Hence, in the usual attitude of 

 standing, the pieces of which the fore limbs are 

 composed are required to be placed more in a 

 straight line than those of the hinder limb; for 

 the power of a column to support a weight is the 

 greater in proportion as it approaches to the per- 

 pendicular position. The hind limbs are composed 

 of exactly the same number of divisions ; but the 

 separate portions are usually longer than those of 

 the fore extremity ; and, consequently, if they had 

 been disposed vertically in a straight line, they 

 would have elevated the hinder part of the trunk 

 to too great a height compared with the fore part. 

 This is obviated by their forming alternate angles 

 with one another. As the pelvis connects the spine 



VOL. I. F F 



