246 HENRY H. DONALDSON 



Turning now to an examination of the tables 1 and charts it is 

 seen that the absolute increase in the weight of the skeleton (chart 

 1) is somewhat rapid at first; indeed, the data (table 2) show 

 that up to 15 grams of body weight the skeleton grows more rapidly 

 than the rest of the body (chart 2), and as a result its relative 

 weight increases; but after that the growth is slower, so that the 

 value of the skeleton weight (observed) on the body weight falls 

 (table 2) from 10.6 per cent at a body weight of 15 grams to 

 about 5 per cent at a body weight of 485 grams. If the weights 

 of the skeleton are corrected for the action of the macerating 

 fluid (table 34, Appendix 2) then the foregoing percentages 

 become, respectively, 12 per cent and 5.2 per cent. 



On looking at the graphs and tables for the axial and appen- 

 dicular skeletons, we see that the weight of the appendicular 

 is always smaller than that of the axial skeleton, but after a 

 body weight of 15 grams, the graphs for relative weights of the 

 two portions (chart 2) are nearly similar in their general course. 

 The mature relations between the two parts of the skeleton are 

 attained therefore at about twenty-two days, which is shortly 

 before the time of weaning. 



The striking feature in this last comparison is the approximate 

 constancy in the weight relations of the two divisions of the 

 skeleton from an early age, although the appendicular division 

 grows just a trifle more slowly than the axial; falling, with slight 

 fluctuations, from 62 per cent of the axial skeleton at 15 grams 

 to 57 per cent at 485 grams, as shown by the values in Table 2. 



1 Intervals used in tables. 



On body length: up to 95 mm. of body length values are given at intervals of 

 2.5 mm. From 95 mm. to 195 mm. at intervals of 5 mm. Above 195 mm. at 

 intervals of 10 mm. 



On body weight: up to 100 grams of body weight values are given at intervals 

 of 5 grams. From 100 grams to 250 grams at intervals of 10 grams. Above 250 

 grams at intervals of 20 grams. The last interval is 15 grams. 



On skeleton weight: up to 7 grams of skeleton weight values are given at 

 intervals of 0.25 gram. Above 7 grams at intervals of 1 gram. Special intervals 

 are used in tables 6 and 7 giving the proportional weights of parts of the limbs. 



Values falling between those entered in the tables may be obtained by simple 

 interpolation. 



