DEVELOPMENT OF THE BODY AFTER BIRTH. 811 



ossification of the tooth-pulp. The fully-formed teeth emerge from the 

 gums in the following order. The central incisors in the seventh month 

 after birth ; the lateral incisors in the eighth month ; the anterior molars 

 at the end of the first year; the canines at a year and a half; and the 

 second molars at two years (Kblliker). The eruption of the teeth in 

 the lower jaw generally precedes by a short time that of the correspond- 

 ing teeth in the upper jaw. 



During the seventh year a change begins to take place by which the 

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

 set, which are different in number, size, and shape from the preceding. 

 The anterior permanent molar tooth 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 bicuspid 

 teeth. In the twelfth year, the canine teeth are changed. In the thir- 

 teenth year the second permanent molars show themselves ; and from 

 the seventeenth 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 ; namely, on each side, above and below, two 

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



The generative apparatus, which is still 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 at this 

 period, and the distinction between the sexes becomes more marked. 

 The beard is developed in the male ; and in the female the breasts as- 

 sume 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 expression. After 

 this period, the muscular 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 develop- 

 ment is then complete. 



