98 



DIGESTION 



opening at the base of each fang through which the nerves 

 and blood vessels communicate with the rest of the body. 

 The blood supphes the epithelial cells with the material 

 out of which they build the tooth, and the nerves probably 

 direct this process. In some animals the teeth grow 

 throughout Ufe, but in man their growth ceases upon the 

 attainment of a certain size. 

 Digestive action of the teeth. — The teeth grind and 



Fig. 28 — The tongue. 



break the food into small particles, and thus prepare it for 

 the solvent action of the digestive juices. If the food is 

 not properly chewed its solution is necessarily delayed just 



