134 THE GROWTH OF THE BRAIN. 



cally they are just as abnormal. Pathological hyper- 

 plasia of brain substance suggests itself to explain some 

 of these cases. The brain is sometimes described as 

 expanding on the removal of the skull cap, suggesting 

 that it had been compressed during life, and in some of 

 these cases part of the excessive growth is due to an 

 increase in the supporting tissues, but further data are 

 wanting. 



From this survey we finally come back to the very 

 general idea that in the case of the brain, as among all 

 organisms and organs called similar, there may be wide 

 individual variations, and as it is midway between the 

 extremes that the greatest number of cases occur, there- 

 fore we must consider the most numerous forms to be 

 those best adapted to surrounding conditions, and con- 

 sequently also look to them for the most perfect physio- 

 logical reactions. If such reasoning is correct, we should 

 hardly expect to find the best intelligence usually asso- 

 ciated with excessive brain-weight. At the same time, 

 as soon as small or macrocephalic brains are examined, 

 deficiencies in the intelligence appear, and, although 

 there is no exact correspondence between the two forms 

 of loss, yet at the lower end of the series the connection 

 between vanishing intelligence and minimal brain-weight 

 is close. 



In the foregoing paragraphs the variations of the 

 brain-weight among sane persons have alone been 

 described ; it remains for us to examine these rela- 

 tions among the insane, and from the facts in this, 

 quarter select such as will bear upon the problem. The 

 great series of records by Dr. Boyd contains observations 

 on the insane as well as the sane. There were 400 

 observations on insane males and 325 on insane females. 

 Tabulated in the same manner as those for the sane, 

 they stand as follows : 



