52 THE HUMAN BODY 



fourth year, and the lower end in the twenty-first. The separate 

 vertebrae of the sacrum (p. 59) are only united to form one bone 

 in the twenty-fifth year of life; and the ilium, ischium, and pubis 

 unite to form the os innominatum about the same period. Up to 

 about twenty-five then the skeleton is not firmly "knit," and is 

 incapable, without risk of injury, of bearing strains which it might 

 afterwards meet with impunity. To let lads of sixteen or seven- 

 teen row and take other exercise in plenty is one thing, and a good 

 one; but to allow them to undergo the severe and prolonged strain 

 of training for and rowing a long race is quite another, and not 

 devoid of risk. 





