GROWTH OF THE SKELETON 



277 



The symmetrical bones usually give similar values within the 

 limits of the error of observation. All the values reported are 

 means of the measurements of the right and left bones. As at 

 birth all the bones are incompletely calcified, they shrink in 

 drying enormously in the younger rats, the fresh bones losing 

 27 to 32 per cent of their length in the youngest group when 

 dried at 96°C. 



With the increase in age and in calcification this loss on dry- 

 ing diminishes so that at a body weight of 100 grams (about 

 ninety days of age) the amount of loss is less than 2 per cent in 

 the case of all of the bones, and at a body weight of 140 grams 



Chart 17 Length of fresh limb bones in millimeters, on body weight (albino 

 rat). Table 20. 



O Tibia, x Femur, a Ulna. • Humerus. + Radius. 



(about 120 days) it has become less than 1 per cent; the stable 

 condition being attained a little less rapidly in the femur and 

 humerus than in the tibia and ulna. The lengths of the fresh 

 bones in millimeters are given on body weight in table 20, but 

 instead of printing the full tables for the room-dried and oven- 

 dried bones we have merely added a small table (21) of correc- 

 tions which apply to rats above 100 grams in body weight, and 

 by the aid of which one may obtain the room-dried or oven-dried 

 length of any of the bones when the fresh length is given, or indeed 

 may recover the length in any other state of moisture, provided 

 the length in one state is known. 



