128 



IV. II. 



superfluous. While in all other animals it is the lower jaw that 

 is moveable, in the river crocpdile it is exceptionally the upper 

 one.^" This is because the feet in this creature are so excessively 

 sijiall as to be perfectly useless for seizing and holding prey ; ' on 

 which account nature has given it a mouth that can serve for 

 these purposes in their stead. For clearly that direction of motion, 

 which will give the greater force to a blow, will be the more 

 serviceable one in holding or in seizing prey; and a blow from 

 above is always more forcible than one from below. Seeing, then, 

 that both the prehension and the mastication of food are offices 

 of the mouth, and that the former of these two is the more 

 essential in an animal that has neither hands nor suitably formed 

 feet, these crocodiles will derive greater benefit from a motion of 

 the upper jaw downwards than from a motion of the lower jaw 

 upwards. The same considerations explain why crabs move only 

 the upper division of each claw and not the lower. For their 

 claws are substitutes for hands, and so require to be suitable for 

 the prehension of food, and not for its comminution ; for such 

 comminution and mastication is the ofiice of teeth. In crabs, 

 then, and in such other animals as are able to seize their food 

 in a leisurely manner, and are not forced by being constantly in 

 the water to perform this office with the mouth,^^ the two functions 

 are assigned to different parts, prehension to the hands or feet, the 

 division or mastication of food to the mouth. But in crocodiles 

 the mouth has been so franied by nature as to serve both purposes, 

 the jaws being made to move in the manner just described. 



All these animals have a neck, which is the necessary con- 

 sequence of their having a lung. For the windpipe by which the 

 air is admitted to the lung is of some length.^^ If however the 

 definition of a neck be correct, which calls it the portion between 

 the head and the shoulders, a serpent can scarcely be said with 

 the same right as the rest of these animals to have a neck, but 

 only to have something analogous to that part of the body. It 

 • is a peculiarity of serpents, as compared with other animals allied 

 to them, that they are able to turn their head backwards without 

 stirring the rest of the body. The reason of this is that a serpent, 

 like an insect, has a body that admits of being curled up, its 

 vertebrae being cartilaginous and easily bent.^^ The faculty in 

 question belongs then to serpents simply as a necessary con- 

 sequence of this character of their vertebrae ; but at the same 

 692 a. 



