804 



THE TEETH. 



It is just before the shedding of the temporary incisors, i. e. , about the 

 sixth year, that there is the greatest number of teeth in the jaws. At that 

 period there are all the milk-teeth, and all the permanent set except the 

 wisdom teeth, making forty-eight. 



Fig. 562. 



Fig. 562. THE TEETH OP A CHILD OP Six YEARS, WITH THE CALCIFIED PARTS OP THE 

 PERMANENT TEETH EXPOSED (after Henle aud from nature). 



The whole of the teeth of the right side are shown, together with the three front teeth 

 of the left side : in the upper and lower jaws the teeth are indicated as follows, viz. : 

 1, milk-teeth i, inner or first incisor ; i', outer or second incisor ; c, canine ; m, first 

 molar ; m! second molar. 2, permanent teeth I, inner or first incisor ; 1', outer or 

 second incisor; C, canine; B, first bicuspid; B' second bicuspid; M 1 , the first molar, 

 which has passed through the gums ; M 2 , the second molar, which has not yet risen above 

 the gums : the third molar is not yet formed. 



During the growth of the teeth the jaw increases in depth and length, 

 and undergoes changes in form. In the child it is shallow, but it becomes 

 much deeper in the adult. In the young subject the alveolar arch describes 

 almost the segment of a circle ; but in the adult the curve is semi-elliptical. 

 The increase which takes place in the length of the jaw arises from a growth 

 behind the position of the milk-teeth, so as to provide room for the three 

 additional teeth on each side belonging to the permanent set. At certain 

 periods in the growth of the jaws there is not sufficient room in the alveolar 

 arch for the growing sacs of the permanent molars ; and hence those parts 

 are found at certain stages of their development to be enclosed in the base 

 of the coronoid process of the lower jaw, and in the maxillary tuberosity in 

 the upper jaw, but they afterwards successively assume their ultimate 

 position as the bone increases in length. The space taken up by the ten 



