DECIDUOUS TEETH. 107 



appearance. In some cases the denies sapiential take an 

 irret^ular direction, and shoot against the adjoining teeth. 



Infants have a set of deciduous teeth, which differ in several 

 respects from those of adults. They are but twenty in number ; 

 tlie five on each side of each jaw, consist of two incisores, one 

 cuspidatus,and two molares or large grinders. The first of them 

 generally protrudes through the gums between the fourth and 

 eighth months of age ; the last about the end of the second year. 

 They commonly appear in pairs,* which succeed each other at 

 irregular intervals. Those of the lower jaw are, in most cases, 

 the first. The order of their appearance is this : the central 

 incisors appear first, then the external incisors on each side ; 

 after these the first molaris, then the cus-pidatus, and finally 

 the last molaris on each side. There are many deviations 

 from this order of succession, but it takes place in a majority of 

 cases. 



These deciduous teeth become loose, and are succeeded by 

 those which are more permanent, nearly in the same order in 

 which they appeared, but with a progress much more slow. 

 The incisores generally become loose between the sixth and 

 seventh year ; the first molares about the ninth, the cuspidati 

 and the second molares not until the tenth or twelfth, or even 

 fourteenth year. The bicuspides take the places of the infant 

 molares. 



The three permanent molares appear in the following order : 

 the first of them protrudes a short time before the front teeth are 

 shed ; it is the first of the permanent teeth which appears, 

 and is seen between the sixth and seventh year. The second 

 molaris appears soon after the cuspidati and the second bicus- 

 pides are seen. There is then a long interval ; for the last 

 molaris or dens sapiential is seldom seen before the twentieth 

 year, and sometimes not until the twenty-fifth. 



The teeth are formed upon pulpy substances, which are 

 situated in the alveoli, and are contained in capsules. A shell 

 of bone is first formed upon the surface of the pulp, which 



* The two teeth of a pair do not appear at the same precise time, but very 

 near to each other. 



