90 CLASS MAMMALIA. 



Physical and moral development of Man. 



The number of offspring at each parturition of the 

 human species is usually limited to one. The birth 

 of twins does not occur in more than a single in- 

 stance out of five hundred, and very rarely indeed 

 is a greater number produced. The period of ges- 

 tation is nine months. A foetus of a month old is 

 usually about an inch in length ; of two months, two 

 inches and a quarter ; of three months, five inches ; 

 six or seven inches at five months old; eleven, at 

 seven; at eight months fourteen inches, and at 

 nine eighteen. Those which are born under seven 

 months, seldom continue to live. The milk teeth 

 begin to shoot out in a few months after the birth ; 

 at two years old these are twenty in number, and 

 they fall successively towards the seventh year to 

 be replaced by others. Of the twelve back cheek 

 teeth which do not drop out, four appear at about 

 four years and a half old, four at nine years old, the 

 four last do not sometimes make their appearance 

 until the twentieth year. 



The foetus increases more and more in proportion 

 as it approaches the moment of birth, the growth of 

 the child, on the contrary, is in a directly opposite 

 ratio. At its birth it possesses more than one 

 fourth of its destined stature ; one half is attained 

 at two years and a half old ; three fourths at the 

 age of nine or ten. The growth, in height, not un- 

 usually ceases at eighteen. The male of the human 

 species is seldom more than six feet high, and very 



