158 THE BILL. 



formidable. All bills, too, which are used in striking 

 or thrusting with the point, are fortified by ridges, 

 and such bills never have so much curvature in their 

 general shape, as that the line joining the tip and the 

 centre of the base falls anywhere without, or even 

 near the surface of the bill. If they act both by 

 thrusting and by cutting between the edges, the 

 ridge of both mandibles is usually a little arched, 

 the arch in that part being the form which, with an 

 equal quantity of matter, enables the mandibles to 

 compress any substance between them with the 

 greatest force. But if the thrust be the only powerful 

 action of the bill, the ridges of the mandibles are 

 generally concave, v^-ith the curvature increasing 

 towards the base of the bill, something in the same 

 manner as that of the bole of a tree increases near 

 the surface of the ground. This is the outline of 

 greatest stability, and as such it is adapted for 

 lighthouses and other structures which are much 

 exposed to strains from the action of the wind or the 

 waves. In those bills, this enlargement toward the 

 base, over which the tip is generally situated in a 

 perpendicular line, causes the bill to strike with more 

 precision, and also with much less jarring of the 

 cartilaginous substance by which it is united to the 

 bones of the head than if it had any other form. 

 Thus we see that in those organs of birds which have 

 not generally any sensibility or proper motions of 

 their own, the same mechanical perfection is dis- 

 played as in the more sentient or more active parts. 



We need hardly say that the bill or beak is 

 adapted to the general structure of the bird, because 

 all the parts of every organised body, be the organi- 

 sation what it may, are always the best adapted to 

 each other, and to the whole : but there are certain 



