BONE GROWTH. 69 



The weight of the femur per unit bone length is greater than 

 that of the humerus at all ages. The weight of both bones per 

 unit length is greater in the male than in the female in all cases 

 save the femur at 23 days of age. The systemic difference is 

 consistently greater than the sex difference. These differences 

 are structural differences, and indicate, as would be expected, 

 that there is a wider divergency in the nature of the genetic 

 factors concerned in structural differentiation of serially homolo- 

 gous bones, than there is between the sex-differential factors 

 concerned in the development of isotropic bones. 



In the comparison of bone growth in length with bone growth 

 in weight ('25^) it was shown that there is a high degree of 

 positive linear correlation in both weight and length in both 

 sexes, with body weight and length respectively, and that 

 systemic correlation in both length and weight was also positive, 

 linear and high. The values recorded represented the inter- 

 structural association values with the age factor unstabilized. 



TABLE II. 



FIRST ORDER CORRELATION COEFFICIENTS. 



Male. Female. 



Humerus weight and femur weight 



(body weight constant) 0.844 0.0042 0.727 0.0030 



Humerus length and femur length 



(body length constant) 0.647 0.0012 0.402 0.0016 



When the general factors for size are eliminated by stabilizing 

 ('26^) for body weight in the case of the systemic weight re- 

 lations, and for body length in the case of the systemic length 

 relations, by the method for partial correlation, the values in 

 Table II. are obtained. 



It is evident that in both sexes the systemic correlation in 

 weight is greater than the systemic correlation in length. That 

 is to say the reduction from the zero order value is greater in the 

 length than in the weight relations. This signifies that in the 

 growing animal systemic association in length is more dependent 

 on the general size factors for length, than is the systemic 

 association for weight dependent on the general size factors for 

 weight. This is consistent with the fact that the growth capacity 

 of the bones in weight differs more in type and degree from the 



