PARTS OF ANIMALS, IV. xii. 



wards as in the quadrupeds, not outwards as in man." 

 The win_<TS are bent with the convex side outwards, 

 like the forelegs of quadrupeds. It is inevitable that 

 a bird should have two feet, for (a) it belongs essenti- 

 ally to the blooded creatures and (b) it is winged, 

 and (c) four is the greatest number of motion- 

 points which a blooded creature can have. So there 

 are four parts (or limbs) attached to a bird's body, 

 and this corresponds exactly with the other blooded 

 creatures, viz. those that live and move upon the 

 ground. The only difference is that whereas the 

 latter have two arms and two legs (or, if they are 

 quadrupeds, four legs), the peculiarity of birds is 

 that they have wings instead of arms (or forelegs). 

 As its very essence includes the power to fly, a 

 bird must have something which it can stretch out, 

 and wings provide this.^ So it remains that of ne- 

 cessity a bird shall have two feet : these with the two 

 wings bring up the number of its motion-points 

 to four. 



All birds have a sharp-edged, fleshy breast : 

 sharp-edged, for flying (a wide surface displaces so 

 much air that it impedes its own motion) ; fleshy, 

 because a sharp-edged thing is weak unless it has 

 a good covering. 



Below the breast is the stomach, which extends (as 

 in the quadrupeds and in man) as far as the residual 

 vent and the point where the legs join the body. 



Those are the parts, then,w^hich have their situation 

 between the wings and the legs. 



Birds, in common with all animals which are pro- 



tive 7tt7)tlk6v in the next line. Literally, the passage reads : 

 " for it is at these [viz. the wings] that birds are stretchable ; 

 and flight-ability is included in the essence of a bird." 



407 



