104 THE VITAL FUNCTIONS. 



consolidated into one piece in each jaw, forming, by their 

 union, the beak of the parrot, in a manner perfectly analo- 

 gous to that which leads to the construction of the compound 

 tooth of the elephant, and which I shall presently describe. 

 The original indentations are obliterated as the beak ad- 

 vances in growth; but they are permanent in the bill of the 

 duck, where the structure is very similar to that above de- 

 scribed in the embryo of the parrot. 



3. Mastication by means of Teeth. 



THE teeth, being essential instruments for seizing and 

 holding the food, and effecting that degree of mechanical di- 

 vision necessary to prepare it for the chemical action of the 

 stomach, perform, of course, a very important part in the 

 economy of most animals; and in none more so than in the 

 Mammalia, the food of which generally requires considera- 

 ble preparation previously to its digestion. There exist, ac- 

 cordingly, the most intimate relations between the kind of 

 food upon which each animal of this class is intended by na- 

 ture to subsist, and the form, structure, and position of the 

 teeth; and these relations may, indeed, be also traced in the 

 shape of the jaw, in the mode of its articulation with the 

 head, in the proportional size and distribution of the mus- 

 cles which move the jaw, in the form of the head itself, in 

 the length of the neck, and its position onthe trunjt, and, 

 indeed, in the whole conformation of the skeleton. But 

 since the nature of the appropriate food is at once indicated 

 by the structure and arrangement of the teeth, it is evident 

 that these latter organs, in particular, will afford to the na- 

 turalist most important characters for establishing a systema- 

 tic classification of animals, and more especially of quadru- 

 peds, where the differences among the teeth are very consi- 

 derable; and these differences have, accordingly, been the 

 objects of much careful study. To the physiologist they 

 present views of still higher interest, by exhibiting; most 



