THE DIGESTIVE SYSTEM. 



163 



or any washing soda. If there be enough time, let each 

 pupil make a drawing of one of each of the four kinds of 

 teeth ; and it would be well to draw both a front (outer 

 surface) and a side view (surface adjacent to another 

 tooth) of each of the four kinds. 



Longitudinal Section 



Side View 



Face View 



Hole for Blood Tubes and Nerves 

 Fig. 55. 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, a more or less constricted part, dividing 

 the crown from the root ; it is normally at about the sur- 

 face of the gum. 



4. A hole at the tip of the root. 



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

 tudinal section of a tooth as follows : Imbed 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. 55. Make a drawing of the surface thus exposed, naming the 

 parts. If human teeth cannot be obtained, almost any kind will serve. 

 Let each pupil keep his preparation. 



