OF THE GIZZARD. 289 



XV. 



OF THE GIZZARD. 



The gizzard is a favourite illustration with our 

 author ; he takes it up in Chaps, x. xii. xv. xvi., as 

 the example of compensation, relation, &c. 



The bill of a bird has extensive relations both 

 externally and internally. When v^e see a bird 

 trimming his feathers with his bill, and combing 

 out each feather from the root to the point, we 

 cannot but observe, that admirably as feathers are 

 formed for flight and for protection against cold 

 and wet, they would be inconsistent with the 

 tongue and teeth of the quadruped. The rough 

 tongue would not penetrate to their interstices ; 

 nor would the ruder operation of the dog's teeth 

 suit the delicate texture of the quills. The bill, 

 therefore, implies the absence of teeth and of sali- 

 vary glands. Lips and muscular cheeks are ne- 

 cessary for mastication ; and however familiar the 

 operation may be, a chapter might be well occu- 

 pied to show how cheeks and lips, salivary glands 

 and teeth, must co-operate before a morsel can be 

 swallowed,* and how the derangement of one fila- 



* See a paper on this subject, in treating of the nerves of mas- 

 tication, in " Phil. Trans." for 1829. 



26 



