466 APPLIED BIOLOGY 



and forward until you feel the shape, position, and texture of the 

 hard and soft palates. Press down upon the tongue with a clean 

 (sterile) glass rod, or the handle of a spoon, and examine the small 

 prolongation of the soft palate which touches the tongue when that 

 is not depressed. This is the uvula. 



386. The Teeth. (L) Examine your teeth, again using the hand- 

 mirror, taking the following description as a guide : Beginning at the 

 middle line at the front of each jaw, there are in order the following 

 kinds of teeth in half of either the upper or the lower jaw : First, two 

 chisel-shape cutting teeth (incisors, meaning to cut into). Next, a 

 tooth with a more pointed edge, which corresponds to the great fangs 

 of dogs and cats and other animals which must hold their prey ; hence 

 the name canine or dog-teeth. The tusks of boars and walruses are 

 enormously enlarged canine teeth. Elephants' tusks are upper in- 

 cisors. Next back of the canine tooth on each side there are an the 

 first or "milk-set" of teeth two grinding teeth (molars). This makes 

 a total of twenty teeth in the first or milk-set, which are deciduous. 

 In adults there are in each half of a jaw two teeth called bicuspids 

 (meaning two cusps or points) in place of the two molars of child- 

 hood; and back of these are three molars, often called "wisdom 

 teeth." There are, therefore, twelve molars in adults in addition 

 to teeth in the places occupied by the twenty teeth of the first or 

 deciduous set, making a total of thirty-two for the adult. 



The incisor teeth begin to appear in children at six or 

 eight months of age, and the full milk-set is present after 

 eighteen to twenty-four months. The loss or shedding of 

 these, caused by growth of new teeth below, occurs at various 

 times between seven and twelve years of age. The perma- 

 nent teeth begin with the incisors at seven or eight years 

 and are completed with the appearance of the molars or 

 wisdom teeth at between sixteen and twenty years of age. 

 The growth of the teeth through the fleshy tissue (gums) 

 is often called " cutting teeth/' 



The structure may be studied by breaking open an ex- 

 tracted tooth, or better by studying a thin section prepared for 

 microscopic use. There is a central cavity which, during the 

 life of the tooth, is filled with a soft mass composed of con- 



