86 



HUMAN BIOLOGY 



2. Chew or grind a piece of apple or bread. 



a. Describe the motion of the jaws in grinding food. 



b. In what part of each jaw are found the teeth that are 



used in grinding or chewing food (Fig- 28) ? 



c. Describe the shape and grinding surface of these 



teeth. incisors 



3. There are two kinds of ,'•: na„i„« 



cutting or biting 

 teeth (Fig. 28), the 

 incisors (Latin, in- 



cisum, from incidere /^SyHKH^K'Tlfc^ ~v-" bicuspids 

 = to cut into), and 

 the canines (Latin, 

 canis =dog, so- 

 called because they 

 often resemble the 

 pointed teeth of a 

 dog). 



There are also two kinds of grinding teeth, the bicuspids 

 (Latin, bi = two + cuspis = point), and the molars 

 (Latin, molaris = a millstone). 



a. (Optional.) Human teeth may be obtained from a dentist. 



They should be cleaned by boiling them in strong caustic 

 soda solution, then in water. If possible, each student 

 should examine and draw one of each of the kinds of 

 teeth named above. 



b. Determine by the use of a mirror the number of teeth 



of each kind that you have and record the numbers 

 in a table in your notebook as follows : — 



- ^ molars 



Fio. 28. — Teeth in upper jaw. 



