111. I. 59 



a time while triturating the food, the water would run into their 

 digestive cavities. Their teeth therefore are all of the sharp kind, 

 so as to serve for comminution of their food, and at the same 

 time are numerous, and set in many parts, that by their very 

 abundance, in the absence of any grinding faculty, they may 

 mince the food into small bits.^ Their teeth are also curved, 

 because these are almost the only weapons which they possess.^^ 



In all these offices of the teeth the mouth also takes its part ; but 

 besides these functions it is subservient to respiration, in all such 

 animals as breathe and are cooled by external agency. For 

 nature, as already said,^^ uses the parts which are common to all 

 animals for many special purposes, and this of her own accord.^^ 

 Thus the mouth has one universal function in all animals alike, 

 namely its alimentary office ; but in some, besides this, the special 

 duty of serving as a weapon is attached to it ; in others that of 

 ministering to speech ; and again in many, though not in all, the 

 office of respiration. All these functions are thrown by nature 

 upon one single organ, the construction of which she varies 

 so as to suit the variations of office. Therefore it is that in some 

 animals the mouth is contracted, while in others it is of wide 

 dimensions. The contracted form belongs to such animals as use 

 the mouth merely for nutritive, respiratory, and vocal purposes ; 

 whereas in such as use it as a means of defence it has a wide 

 gape. This is its invariable form in such animals as are saw- 

 toothed. For seeing that their mode of warfare consists in biting, 

 it is advantageous to them that their mouth shall have a wide 

 opening ; for the wider it opens, the greater will be the extent of 

 the bite, and the more numerous will be the teeth called into play. 



What has just been said applies to fishes as well as to other 

 animals ; and thus in such of them as are carnivorous, and made 

 for biting, the mouth has a wide gape ; whereas in the rest it is 

 small, being placed at the extremity of a tapering snout. For 

 this form is suited for their purposes, while the other would be 

 useless. 



In birds the mouth consists of what is called the beak, which in 

 them is a substitute for lips and teeth. This beak presents 

 variations in harmony with the functions and protective purposes 

 which it serves. Thus in those birds that are called Crooked- 

 clawed^^ it is invariably hooked, inasmuch as these birds are 

 carnivorous, and eat no kind of vegetable food whatsoever. For 

 662b. 



