The Digestive System. 



157 



keep the food between the teeth. When the morsel of 

 food is sufficiently masticated, the tongue pushes it back 

 into the pharynx to be swallowed. 



The Teeth. The teacher can usually obtain a supply of teeth from 

 the dentist for the asking. These should be cleaned before using them 

 in the class. Use pearline or any washing soda. Let each pupil make 

 a drawing of one of each of the four kinds of teeth ; draw both a front 

 (outer surface) and a side view (surface adjacent to another tooth) of 

 all but a molar. 



Longitudinal Section 



Side View 



Face View 



Enamel 



Crown 



Neck 



Root 



for Blood Tubes and Nerves , 



Fig. 67. Parts of a Tooth. (Incisor.) 



External Features of a Tooth. Examine one of the 

 front teeth. It has the following parts : 



1. The crown, the part that is above the gum. 



2. The root, the part that was buried beneath the gum. 



3. The neck, dividing the crown from the root. 



4. A hole at the tip of the root. 



To make a Section of a Tooth. Let each pupil prepare a longitudi- 

 nal section of a tooth as follows : Embed a tooth in a little sealing wax 

 on the end of a spool, cork, or block of wood. With a grindstone grind 

 away one half, showing the pulp cavity to the tip of the root, as in 

 Fig. 67. Make a drawing of the surface thus exposed, naming the 



