CHAPTER VI. 



COMPARATIVE FORMS OF THE BILLS OF BIRDS, 

 ILLUSTRATIVE OF THEIR HABITS. 



The armature of the jaws of birds, which answers 

 the same purpose in their economy which the lips and 

 teeth do in that of mammalia, always consists of two 

 mandibles, one placed over the other, and opening 

 and shutting' chiefly by the motion of the lower one. 

 This organ is sometimes called a bill, and sometimes 

 a beak, but the distinction of these names is not very 

 clear. Bill is, however, the more general of the two, 

 in the usage ; for all beaks may be called bills, but 

 all bills cannot be called beaks. According to the 

 popular understanding, which, rather than any etymo- 

 logical definition, is the rule in popular language, the 

 mandibles of a bird, in order to entitle them to the 

 name " beak," require the three attributes of firmness 

 of texture, power, which requires considerable depth 

 and breadth in proportion to the length, and curva- 

 ture downwards, with pointedness at the tip of the 

 upper mandible, and projection of it over the under 

 one ; but the precise degree in which these are 

 required, as well as their relative proportions to each 

 other, are indeterminate. Those to which the term 

 beak is more generally applied are the mandibles of 

 birds of prey, and those of the parrot tribe, and some 

 other vegetable or omnivorous feeders which use this 



