290 



II I'.NKY II. DONALDSON 



The second large relation is between the growth in length of 

 the proximal and the distal bones of the limbs. In both the fore 

 and the hind limb the growth of the proximal bones is at first less 

 rapid than that of the distal bones, giving the peculiar form 

 of graph shown in chart 22. After a body weight of 20 to 35 

 grams the relative growth of all the distal bones becomes less 

 rapid, falling off steadily in the case of the tibia and the ulna, 

 and showing a slight fluctuation in the case of the radius. 



50 



30 



50 



100 



Growth of Skeleton— Albino Rat 

 Fresh 



150 



Ratios of Bone lengths 



2C0 



250 



300 



350 



BODY WEICHT IN CRAMS 



lii m iii i i i n i i iiB 



400 



450 



Chart 23 Ratios of fresh lengths of homologous limb bones, on body weight 

 (albino rat) Table 28. 



Humerus Ulna Radius 



Femur 



x 



Tibia 



o 



Tibia 



When the ratios of the lengths of the humerus plus radius, 

 humerus plus ulna, and femur plus tibia are taken on the body 

 lengths, as in table 29, there appears rather a high degree of 

 constancy in all cases after a body length of 125 mm., equivalent 

 to about 50 grams in body weight. 



