ON THE WALK OF QUADRUPEDS. 15 



are at rest, as in the walk of a man (bipedis) by the movement of one 

 foot constantly succeeding that of the other. Under this erroneous 

 impression, the ancients observed that quadrupeds, while they stand 

 upon the four soles of their feet, form upon the ground a four-sided 

 figure, A B CD. It was thence remarked, that when they are at full 

 speed, the two fore feet, A B, are raised and moved forward together, 

 whilst both the hind feet, C D, are at rest. Immediately after 

 A B falls to the ground, the two hind feet, C D, are raised and moved 

 forwards near to A B ; and in this manner quadrupeds, by successively 

 contracting and lengthening themselves, perform running, as is evident 

 in the case of horses and dogs at full speed. 



But in going at an easy pace, it is evident that the two fore feet or 

 the two hind feet are not raised together, nor moved forwards at the 

 same time, but alternately; when A is moved, B is at rest; and, on the 

 contrary, when B moves, A is at rest. It is certain that this takes 

 place in the hind feet : but it cannot be so easily distinguished in what 

 order the fore feet move with the hind feet — I mean whether the two 

 left feet, A and D, are moved at the same time, or A with C, on 

 account of the quickness of the motion. 



They were of opinion, however, that this could be ascertained 

 by a process of reasoning. If the two left feet, A D, were raised and 

 moved forwards at the same time, then the animal would fall upon the 

 left side. Therefore, the right fore foot, B, with the left hind foot, D, 

 ought rather to rise and move forward at the same time, so that the 

 feet diametrically opposite might move or rest together. Moreover 

 this erroneous opinion prevailed to so great a degree, that, in equestrian 

 statues of marble and of bronze, both ancient and more recent, the two 

 -feet diametrically opposed are suspended from the ground. 



