286 



HENRY H. DONALDSON 



has been in progress since the fetal period, at which time these 

 bones are characteristically short, thick, and clumsy. 



In order to illustrate these changes, figure 1 is given in which 

 is shown at A, B, and C the left femur at three ages, as described 

 in the legend to the figure. 



B 



C 



D 



E 



Fig. 1 Showing the form of the oven-dried femur at several different ages. 

 A, B, and C represent the relative lengths and the shapes of the bones desig- 

 nated, while D represents B photographically enlarged to the length of C and E 

 represents A similarly enlarged. 



The data for the albino rats from which these oven-dried bones were taken 

 are as follows: 



A. 

 B. 

 C. 



One notes the relative overdevelopment of the extremities of 

 the bones in the younger animals. At D is shown the bone B 

 enlarged to the length of ( 1 , and at E the bone A similarly en- 

 When these enlarged younger bones are compared with 



larged. 



