PARTS OF ANIMALS, IV. xi. 



up : this, and biting, is the business of the teeth). 

 In crabs, then, and in other creatures M'hich, because 

 their mouth does not come into action while under 

 water, can take their time about seizing their food, 

 the labour is divided : they seize their food \vith 

 their hands or feet, and cut it up and bite it Λvith 

 the mouth. For the crocodile, hoAvever, by making 

 the jaws move as I have described. Nature has 

 constructed a mouth which can be used for both 

 these purposes. 



All these animals have also a neck ; this is because 

 they have a lung and there is a long windpipe through 

 which they admit the breath to it. 



Since the neck is the name given to the part of 

 the body betΛveen the head and the shoulders, the 

 serpent would appear to be the very last of these 

 creatures to possess one : at any rate, if the neck is 

 to be defined by the limits mentioned above, he has 

 merely something analogous to a neck. Compared 

 with kindred animals, serpents have this peculiarity : 

 they can turn their heads backAvards Avhile the rest of 

 the body remains still. The reason is that their body 

 (like an insect's) can roll up ; the vertebrae are cartila- 

 ginous and flexible. This, then, is the necessary cause 

 why they have this ability; but it serves a gooc? purpose 

 too, for it enables them to guard against attacks from 

 the rear, and with their long bodies devoid of feet 

 they are ill adapted for turning themselves round to 

 keep watch over the rear. To be able to raise the 

 head and yet unable to turn it round would be useless. 

 These animals have also a part which is a counter- 

 part to the breast. But they have no mammae either 

 here or elsewhere ; nor have any of the birds or fishes. 

 This is because the mammae are receptacles, vessels, 



399 



