690 DEVELOPMENT OF THE BODY AFTER BIRTH. 



the first set of teeth are thrown off and replaced by a second or 

 permanent set, differing in number, size, and shape from those 

 which preceded. The anterior permanent molar first shows itself 

 just behind the posterior temporary molar, on each side. This 

 happens at about six and a half years after birth. At the end of 

 the seventh year the middle incisors are thrown off and replaced 

 by corresponding permanent teeth, of larger size. At the eighth 

 year a similar exchange takes place in the lateral incisors. In the 

 ninth and tenth years, the anterior and second molars are replaced 

 by the anterior and second permanent bicuspids. In the twelfth 

 year, the canine teeth are changed. In the thirteenth year, the 

 second permanent molars show themselves ; and from the seven- 

 teenth to the twenty-first year, the third molars, or " wisdom teeth," 

 emerge from the gums, at the posterior extremities of the dental 

 arch. (Wilson.) The jaw, therefore, in the adult condition, contains 

 three teeth on each side more than in childhood, making in all 

 thirty-two permanent teeth ; viz., on each side, above and below, 

 two incisors, one canine, two bicuspids, and three permanent 

 molars. 



The entire generative apparatus, which is still altogether inactive 

 at birth, begins to enter upon a condition of functional activity 

 from the fifteenth to the twentieth year. The entire configuration 

 of the body alters in a striking manner at this period, and the dis- 

 tinction between the sexes becomes more complete and well 

 marked. The beard is developed in the male ; and in the female 

 the breasts assume the size and form characteristic of the condition 

 of puberty. The voice, which is shrill and sharp in infancy and 

 childhood, becomes deeper in tone, and the countenance assumes a 

 more sedate and serious expression. After this period, the mus- 

 cular system increases still further in size and strength, and the 

 consolidation of the skeleton also continues ; the bony union of its 

 various parts not being entirely accomplished until the twenty-fifth 

 or thirtieth year. Finally, all the different organs of the body 

 arrive at the adult condition, and the entire process of development 

 is then complete. 



