USES OF THE PAKROT's BILL. 21 i 



instinct, but of one which, as is the case with all 

 instincts, it is vain to hope for an explanation upon 

 the principles of reason. 



The leading uses of the parrot's bill are, breaking 

 hard vegetable substances, and climbing. A pair of 

 nutcrackers is the nearest comparison to it in artificial 

 instruments, but the bill is beyond all comparison the 

 more universal and effective. This bill does not snap 

 or acquire any force of momentum before it comes 

 in contact with the substance to be acted on. It 

 works wholly by pressure ; but the pressure is accom- 

 panied by a sliding motion, which differs with the 

 degree of exertion. The lower mandible is raised by 

 very powerful muscles, and it is at the same time 

 pushed a little forwards ; the upper mandible has 

 much less motion than the lower, but still it has more 

 than in most birds ; and when the bill is exerted with 

 great force, it has a motion downwards and back- 

 wards at the same time. The substance acted on is 

 thus wTcnched round at the same time that it is pressed 

 by the cutting edges of the mandibles ; and every 

 one who has attended to the subject, knows how very 

 much a cutting operation is assisted by accompanying 

 it with a wrenching one. 



The muscles which move the mandibles are very 

 powerful, and give that peculiar fulness which appears 

 in all the cheeks of the tribe ; and the motion of the 

 upper mandible, limited as it is in space, brings the 

 whole of them into action. It is these compound 

 motions of the working parts of animals, which enable 

 them to act with so much less exertion than our 

 mechanical contrivances ; and taking time and effect 

 both into the estimate, there is no tool by means of 

 which the shell of a hard nut could be broken, with- 

 out the expending of far more than double the power 

 p2 



