A STUDY OF BLOOD MANUFACTURE 111 



tusks of the walrus. The arrangement of teeth in the mouth 

 of a dog is represented in the dental formula, 



.3 + 3 1+1-4+4 TO 2+2_ 42 

 ' ~ 



Iii the group of the her-biv'o-ra } which includes the animals 

 that feed wholly upon vegetation, the huge premolars and 

 molars are of special use ; they grind up the grass and grain 

 like millstones. A horse's dentition is represented by the 

 formula, 



3+3 1+1 4+4 3+3 _ dl 

 3+3' T+i' P 4+4:' S+S~ 



The incisors of a horse are well developed, but the canines 

 seldom push through the gums. In the space between the 

 incisors and premolars, man puts the horse's bits. A cow 

 has no incisors in the upper jaw, and the canines are also 

 wanting. 



Since man has all of the four kinds of teeth developed in 

 about equal proportions, he is evidently well fitted to eat 

 both animal and vegetable tissues, and a well-rounded diet 

 should include a great variety of food materials. 



The Tongue in Other Animals. The tongue of frogs and 

 toads is attached just inside the mouth opening, and its free 

 end, when the mouth is closed, extends backward toward 

 the gullet. In securing the insects upon which it largely 

 feeds, the animal opens its mouth and thrusts forward the 

 sticky end of the tongue, which captures the fly or bee. The 

 end of the tongue is then quickly withdrawn into the 

 mouth, and the food is swallowed at once. The snake uses 

 its forked tongue principally as an organ of feeling, darting 

 it from its mouth with great rapidity. This tongue is per- 

 fectly harmless. Among the carnivora the upper surface 

 of the tongue is covered with strong papillae. This enables 

 the dog, cat, lion, or tiger to scrape the meat from bones 

 and to extract the marrow after the bones are broken open. 



