DURING POST-NATAL DEVELOPMENT. 



age respectively of 7.92, 8.96, 9.87, and 10.9 years. The relative sitting-height of 

 these groups is respectively 53.5 per cent, 53.4 per cent, 53.2 per cent, and 54.3 

 per cent. The nearest general age-group stature given by Boas and Wissler is that 

 of 127.8 5.5 cm. for the age of 9. For this age the sitting-height is given as 68.5 

 3.0. The relative sitting-height is therefore 53.6 per cent of the stature, the same 

 as that found as the average for the whole group of boys of 126 to 126.9 cm. stature. 



For head-girth Hastings gives 52.49 cm. as the mean for the 9-year group 

 (stature 125.86 cm.). The relative head-girth is therefore 41.7 per cent. For the 

 125 cm. group, age 8, the relative head-girth is 42 per cent; for the 127 cm. group, 

 age 8, it is 41.8 per cent; for the 126 cm. group, age 9, it is 41.4 per cent; for the 126 

 cm. group, age 10, it is 41.3 per cent. Ernst (1906) gives individual data on head- 

 girths of Swiss school children, 8 to 15 years of age, which make possible a com- 

 parison between groups based on stature and on age. For age 8 to 9 Ernst found the 

 mean stature of boys to be 126.1 cm., the mean head-girth 52.0 cm., the relative 

 head-girth 41.3 per cent. For age 9 to 10 the mean stature was likewise 126.1 cm., 

 the mean head-girth 52.0 cm., and the relative head-girth 41.3 cm. Between the 

 ages of 8 and 11 she gives data on 10 boys with a stature between 126.0 and 126.8 

 cm. (average 126.35). The average relative head-girth for this group is 41.06. 



When stature-groups are used the variability of the different measurements is 

 much less than when age-groups are used. Ernst has given data which make it 

 possible to compare the mean variability of certain measurements according to 

 stature and age-groups. The following data illustrate the greater variability in the 

 age-groups : 



TABLE 10. 



The data of Boas and Wissler (1904) likewise make it possible to compare the 

 variability of measurements in age-groups with those in stature-groups : 



TABLE 11. 



This table shows greater variability in the age-groups than in the stature- 

 group in all measurements except that of width of head in girls. 



