54 THE GROWTH OF THE BRAIN. 



increase in weight just noted. On comparing the curve 

 for the females with that for the males, by far the most 

 striking feature is the similarity of the two. This is the 

 more to be emphasised as in the further discussion it is 

 the points of difference which will be specially described. 

 The curve for the weight of the females follows that for 

 the males very closely up to the sixteenth year ; at that 

 time there commences a divergence which is most 

 important, and which leaves the females during the 

 remaining years of life some 25 Ibs. or more behind 

 the males. This divergence is brought about by a 

 period of more vigorous growth in the males between 

 the fifteenth and eighteenth years. 



But before reaching this point of final separation, 

 there are in these curves at least three features of great 

 interest. Both curves start at birth from almost the 

 same point, that for the male, however, being slightly 

 higher, thus indicating that at birth the male infant is 

 heavier. Up to the end of the first year the curves 

 diverge rapidly, and since the steeper curve indicates 

 the greater absolute increment, we see at once that the 

 male has grown more during this time. From this point 

 to the tenth year the two curves diverge much more 

 slowly, running at times quite parallel to one another. 

 About the eleventh year the curve for the female becomes 

 more perpendicular. The curve for the male still con- 

 tinues at the same angle as before, and the result is, 

 that at the twelfth year, or a little later, the curves 

 converge, and, being close together, that for the females 

 crosses that for the males. From this point to the 

 sixteenth year the girls are heavier than the boys. 

 This second period is closed, as the curve for the female 

 becomes more horizontal and that for the male more 

 perpendicular, so that they again cross. Beyond this 

 is the wide divergence already described. In both the 



