66 FREDERICK S. HAMMETT. 



might be noted that the growth capacity of the femur in length 

 generally tends to be slightly greater than that of the body, 

 while that of the humerus is less. 



Attention should be directed to the fact that in both sexes there 

 occurs at 65 days of age an approximation of the growth capacity 

 values in body weight and length to a common level, which is 

 quite the same in character as that exhibited by the bones and 

 their constituents, and which is similarly interpretable. 



The foregoing analysis demonstrates that the systemic factors 

 participating in the determination of bone growth are largely 

 productive of differences in the degree rather than in the course 

 of development. 



Turning now to the inter-sex comparison it is seen from Table I 

 that both bones are consistently slightly heavier and longer in 

 the male than in the female save at 23 days of age. The direction 

 of sex difference in the bones, however, is at all ages positively 

 correlated with the direction of sex difference in body size. 



A study of Chart I reveals the fact there is no consistent 

 direction of sex difference in growth capacity of the bones on age. 

 At 30 and at 75 days of age the growth capacity values are greater 

 in the female than in the male; at 23, 50, and 100 days the 

 reverse is the case, while at 65 days the differences are incon- 

 siderable. It is to be noted, however, that the differences in 

 growth capacity values induced by sex-specific factors affect the 

 bone as a whole and not differentially, in so far as the direction of 

 difference is concerned. 



Notwithstanding the inconsistency of sex difference on age, it is 

 a fact that the sex difference in growth capacity in length of both 

 bones is generally less than the sex difference in weight. As a 

 result the degree of sex difference of the bones in length is less 

 than that in weight at all ages. 



The general principle is derived from this and the similar 

 relation exhibited in systemic development, that the cliffer- 

 of the long bones during growth is due more to the 

 * of growth by increments in weight than to those con- 

 cerned in growth by increments in length. 



substantiated by the fact that the increase in sex 

 curs in both bones, is greater in the weight 

 than in the length relation. 



