Franklin P. Mall. 



sulcus communicates with the fissure of Sylvius in 3 per cent of the 

 cases it is called a variation in 3 per cent of the cases, while in the 

 remaining 97 per cent it is normal. In this way I obtained a column 

 of 73 records, representing the norm as well as the variations for each 

 hemisphere both of the male and the female. The average of these 

 figures is as follows. 



This table indicates that the brain of woman is not nearer the norm 

 but varies less than does that of man. Could all the variations 

 found be groujx^d together in single brains, leaving the rest a§ per- 

 fectly normal, then 76 brains of men and 81 of women out of our 100 

 would be exactly normal in the arrangement of the gyri and sulci. 



Retzius has done us a great service in pointing out the way by 

 which this problem can be attacked by the statistical methods. A few 

 remarks regarding his conclusion may be made, but before they can 

 be criticised properly it will be necessary to tabulate many other 

 brains, as he has done, of both men and women. 



In the first column of figiires in Retzius' table regarding the fissure 

 of Sylvius both the norm and the variation is given, but the missing 

 figures can easily be obtained by subtracting the given percentage from 

 100. In case the average of a given record is more than 50 in both 

 male and female, it is called normal, while when it is less it is called 

 a variation. Thus the central sulcus anastomoses with the sulcus 

 precentralis superior in 18 per cent of the cases and therefore these 

 do not anastomose in 72 per cent. It may be remarked that the 

 number of brains of men studied by Retzius is somewhat small, while 

 that of women is decidedly too small, for in the latter each single 

 record equals 8 per cent when reduced to the scale of 100. 



The data given by Retzius regarding differences in the gyri and 

 sulci due to sex may be criticized from tAvo standpoints. Those in 



