JAWS OF BIRDS. 1 17 



have no teeth ; their office being supplied by 

 the sharp cutting edges of the horny portion of the 

 jaws. 



Birds, as well as serpents, have a moveable upper 

 jaw ; but they are also provided with beaks of 

 various forms, in which we may trace an exact 

 adaptation to the kind of food appropriated to each 

 tribe : thus predaceous birds, as the eagle and the 

 hawk tribe, have an exceedingly strong hooked 

 beak, for tearing and dividing the tlesh of the ani- 

 mals on which they prey ; while those that feed upon 

 insects, or upon grain, have pointed bills, adapted 

 to picking up minute objects. Aquatic birds have 

 generally flattened bills, by which they can best 

 select their food among the sand, the mud, or the 

 weeds at the bottom of the water ; and their edges 

 are frequently serrated, to allow the fluid to filter 

 through, while the solid portions are retained in the 

 mouth. The Duck affords an instance of this 

 structure ; which is, however, still more strongly 

 marked in the genus 3Iergus, or Merganser, where 

 the whole length of the margin of the bill is beset 

 with small sharp pointed teeth, directed backwards : 

 they are particularly conspicuous in the Mergus 

 sermtor, or red-breasted Merganser. 



The beak of the Hcematopiis, or Oyster-catcher, 

 has a wedge-shape, and acts like an oyster-knife 

 for opening bivalve shells. 



In the Loxia curvirostra, or Cross-bill, the upper 

 and lower mandibles cross each other when the 

 mouth is closed, a structure which enables this bird 

 to tear open the cones of the pine and fir, and pick 

 out the seeds by insinuating the bill between the 

 scales. It can split cherry-stones with the utmost 



