CKOWTH OF THE SKELETON 



283 



GROWTH OF THE LONG BONES IN TRANSVERSE DIAMETER 



It is of interest for us to get an idea of the shape of the long 

 bones at different ages and to determine whether there is any 

 progressive change in shape between birth and maturity. It is 

 not possible, however, to do this precisely without a more elab- 

 orate study than we can make now, but it is possible by some 

 simple computations to obtain a rough idea of what is taking- 

 place. 



From the data on the lengths of the fresh bones (table 20) 

 and those on the weights of the fresh bones (table 12) we can 

 compute the weight of a running millimeter, treating the bones 



TABLE 24 

 The relative lengths of the several long bones on body length in rats over 160 mm. in 

 body length {i.e., over 100 grams in body weight). Averages given in three body 

 length groups 



as if they were solid cylinders having their axes equal to the bone 

 lengths. 3 



3 In making the computations which are required, the values just as they 

 appear in tables 12 and 20 have been used. Concerning these a word of com- 

 ment is necessary. The lengths used are those for the single bones — humerus, 

 ulna, femur, and tibia, respectively. The weights, however, are in each instance 

 for both bones — right plus left. Furthermore, the length for the ulna is used 

 as a divisor for the weight of the ulna plus radius (2), and the length for the 

 tibia as a divisor for the weight of the tibia plus fibula (2), so that the signifi- 

 cance of the values for a running millimeter is not exactly the same for the 

 humerus and femur as for the other bones with which they are compared. As, 

 however, it is the change in the weight of the running millimeter rather than its 

 absolute value which is here important, it has seemed best to use the table values 

 as they stand rather than develop new tables for this special purpose. 



