290 COMPARATIVE ANATOMY OF THE TEETH. 



the beak of the bird is an organ of prehension and mastica- 

 tion, and often a powerful weapon for either offence or de- 

 fence, though in its form and structure it is more like the 

 claws and nails than teeth. 



The beak in birds of prey is hard, in water birds it is 

 comparatively soft. The form is very various, and corre- 

 sponds with the kind of food and the habits of the several 

 varieties. In some birds of prey it is curved into a "hook 

 with sharp cutting edges." In others, as in the stork, it is 

 straight; some have it bent downwards, others upwards; 

 some have it compressed, as the penguin, transversely; and 

 others, as the duck, have it flat. 



The jaws present, in some, distinct elevations or notches, 

 resembling teeth. The duck has these indentations regu- 

 larly arranged, and supplied with branches of the inferior 

 maxillary nerve. 



THIKD CLASS OF ANIMALS REPTILES (REPTILIA.) 



The teeth of this class, occupying a position intermediate 

 between those of the bird and of the .fish, are thought to 

 partake thereby of the characteristics of both. 



The tortoise has the beak of the bird, and with this 

 exception all other reptiles are said to have true teeth. 

 These are pointed and conical, and resemble more those 

 of the carnivorous class, and form weapons of attack and 

 defence. 



The number of teeth belonging to reptiles is not deter- 

 mined, but it is greater than in man. They are fixed in 

 the jaws, though sometimes as in the serpent, are placed 

 in the palate. They are without roots, and are fixed in 

 alveoli which are more narrow at their external opening 

 than at the bottom. 



The teeth of this class are developed at a very early age, 

 and always the number is the same. Those which have 

 just come forth from the egg have as many as the adult 

 animal, ten or twenty feet in length. 



Eeptiles shed their teeth, it seems, with greater fre- 

 quency and facility than most other animals, These or- 



