66 Heredity and Child Culture 



ence of the head averages from thirteen to four- 

 teen inches ; at the end of the second year, about 

 eighteen inches; at the seventh year, about 

 twenty and a half inches, and at the completion 

 of growth twenty-two or more inches. 



The spinal column is curved but very flexi- 

 ble. In early infancy, the so-called normal 

 curves are not developed above the pelvis but 

 there is one long curve in the shape of a general 

 convexity. As the child grows older, the spine 

 becomes less flexible and more rigid with in- 

 creased power in the spinal muscles. There is, 

 however, much more flexibility all through early 

 life than obtains in later years. 



In the musculature, the gi*eatest relative 

 strength is shown in the hands and arms for a 

 time after birth. At about three months, the 

 muscles of the neck have developed sufficiently 

 to allow the infant to hold up its head in an un- 

 certain way. At the seventh or eighth months, 

 the muscles of the back have become strength- 

 ened so that the baby can sit up, and shortly 

 after this it may be allowed to creep. Free play 

 should be sdven to the muscles of the arms and 



