PROGRESSION OF ANIMALS, xii.-xiii. 



lift them only a little way from the ground, because 

 the whole of the thigh and the joint from which the 

 shin grows would come up against the belly as the 

 animal advanced. On the other hand, if the bend- 

 ing of the back legs were forward, the raising of the 

 feet would be similar to that of the front feet (for 

 they could only be raised a short distance by lifting 

 the legs, since the thigh and the joint of both legs 

 would come up under the region of the belly), but 

 the bending being, as it is, backwards, there is no- 

 thing to hinder their progression as they move the 

 feet in this manner. Again, for those animals which 

 are suckling their young, it is necessary, or at any 

 rate better, that their legs should bend in this way 

 with a view to this function ; for if they bent their 

 legs inwards, it would not be easy for them to keep 

 their young underneath them and to protect them. 



XIII. Now there are four ways of bending the legs 

 taking them in pairs. Both the fore and the hind 

 legs must bend either concavely, as in figure A ; or 

 in the opposite manner, that is convexly, as in B : 



(Mich, supplies the figures which are lacking in the mss. In each group 

 the front legs are the left pair, the hind legs the right.) 



or inversely, that is to say, not in the same direction, 

 but the forelegs bend convexly and the back legs 

 concavely, as in C ; or (the converse of C) with the 

 convexities towards one another and the concavities 



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