1.30 THE VITAL FUNCTIONS. 



jaws, and partly to the palate. The Cheloiiian 

 reptiles have no teeth ; their office being sup- 

 plied 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 appro- 

 priated to each tribe : thus predaceous birds, as 

 the eagle and the hawk tribe, have an exceed- 

 ingly strong hooked beak, for tearing and di- 

 viding the flesh of the animals on which they 

 prey ; while those that feed on insects, or on 

 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 31ergus, 

 or Mergansor, where the whole length of the 

 margin of the l)ill is beset with small sharp 

 pointed teeth, directed backwards : they are par- 

 ticularly conspicuous in the Mergus serrator, or 

 red-breasted Mergansor. The object of the 

 barbs and fringed processes which are appended 

 to the tongue in many birds, such as that of the 



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