DIGESTION AND ABSORPTION 



301 



that the food may slip down easily. The roof of the mouth is 

 formed in front by a plate of bone called the hard palate, and a 

 softer continuation to the back of the mouth, the soft palate. These 

 separate the nose cavity from that of the mouth proper. The part 

 of the space back of the soft palate is called the pharynx, or throat 

 cavity. From the pharynx lead off the gullet and windpipe, 

 the former back of the latter. The lower part of the mouth 

 cavity is occupied by a muscular tongue. Examination of its 

 surface with a looking-glass shows it to be almost covered in places 

 by tiny projections called papillce. These papillse contain organs 

 known as taste buds, the sensory endings of which determine the 

 taste of substances. The tongue is used in moving food about in 

 the mouth, and in 

 starting it on its way 

 to the gullet ; it also 

 plays an important 

 part in speaking. 



The Teeth. In 

 man the teeth, unlike 

 those of the frog, are 

 used in the mechanical 

 preparation of the food 

 for digestion. Instead 

 of holding prey, they 

 crush, grind, or tear 

 food so that more sur- 

 face may be given for 

 the action of the diges- 

 tive fluids. The teeth 

 of man are divided, ac- 

 cording to their func- 

 tions, into four groups. 

 In the center of both the upper and lower jaw in front are found 

 eight teeth with chisel-like edges, four in each jaw; these are 

 the incisors, or cutting teeth. Next is found a single tooth on 

 each side (four in all) ; these have rather sharp points and are 

 called the canines. Then come two teeth on each side, eight in 



Teeth of the upper jaw, from below. 1, 2, in- 

 cisors; 3, canine; 4. -5, premolars ; 6, 7, 8, molars. 

 II. longitudinal section of a tooth. E, enamel ; 

 D, dentine ; C, cement ; P, pulp cavity. 



