8o 



HUMAN PHYSIOLOGY 



CHAP. 



tion is nourished. A dead tooth is one in which the 

 dentist has taken out the nerve and blood vessels and 

 has filled the root with something else. 



FIG. 41. Showing how the blood vessels and nerves reach the teeth, i, 2, in- 

 cisors ; 3, canine; 4, 5, bicuspids; 6, 7, 8, molars; a, vein; b, artery; 

 c, nerve ; d, vein, artery, and nerve. (From Johonnot and Bouton.) 



70. Mouth Digestion. The large, strong muscles of 

 the cheeks enable us to use the teeth for biting, tearing, 

 crushing, and grinding the solid foods. Cooking has 

 helped to soften the foods, yet in order to dissolve them 

 it is necessary to chew every mouthful thoroughly. It 

 is said of W. E. Gladstone, the great English statesman, 



