u 9 6 HUMAN ANATOMY. 



cal dimension through the hemisphere is about 125 mm. (5 in.). The female brain 

 is commonly somewhat shorter than that of the male, and, therefore, relatively 

 broader and deeper. 



The weight of the brain has been the subject of repeated investigation with 

 results that fairly agree. The conclusions of Handmann 1 , based on recent examina- 

 tions of 1014 brains (546 male and 468 female) from persons ranging in age from 

 fifteen to eighty-nine years, are of interest since they confirm in the main the results 

 obtained from previous observations. The average weight of the adult brain (from 

 15-49 years), without the dura but surrounded by the arachnoid and pia, is 1370 

 grams (48.6 oz. ) for men and 1250 grams (44.4 oz. ) for women. The weight of 

 these membranes, including the enclosed arachnoid fluid, has been estimated at 56 

 gin. and 49 gm. in male and female brains respectively (Broca). The brain usually 

 attains its maximum weight about the eighteenth year, perhaps somewhat earlier 

 in women, no increase taking place after the twentieth year. Subsequent to the 

 sixtieth year in both sexes a progressive diminution occurs, by the age of eighty the 

 brain having lost approximately one-fifteenth of its entire weight (Boyd). Including 

 the brains of individuals between fifty and eighty-nine years in his series, Handmann 

 found the average weight to be 1355 gm. (47.8 oz. ) for men and 1223 gm. (40.3 oz. ) 

 for women. Approximately 81.5 percent, of adult male brains have a weight be- 

 tween 1200 and 1500 gm. ; 8.8 per cent, one of from 950-1200 gm. ; whilst 20.3 

 per cent, possess a weight over 1450 gm. Correspondingly, about 84 per cent, of 

 female brains weigh between 1100-1400 gm. ; 44 per cent, between 1200-1350 gm. ; 

 and 46 per cent, below 1200 gm. The average weight of the brain of the new-born 

 male child is 400 gm. (14 oz. ) and that of the female one is 380 gm. (13.4 oz. ). 

 During the early years of childhood the brain rapidly becomes heavier, its weight 

 being "doubled by the end of the first year and trebled by the completion of the sixth 

 year. At first the increase affects the brain equally in both sexes ; later the young 

 female brain fails to keep pace in its growth with the male one, the differences 

 becoming progressively more marked. 



Whilst the brain-weight and stature stand in direct ratio in the new-born and in 

 children up to 75 cm. in length, irrespective of age and sex, after attaining such stat- 

 ure the relation is irregular and uncertain. Likewise in the adult, Handmann found 

 no constant ratio between the stature and the brain-weight, although in general a 

 lower average weight of the brain is found in short individuals than in those of mod- 

 erate and of large height. The relative brain-weight, as expressed in the ratio 

 between each centimeter of height and the brain-mass, Handmann found to be 8.3 

 gm. for each centimeter of height in men and 7.9 gm. in women, a slightly higher 

 proportion in favor of the male subject being thus observed. The average ratio of 

 the weight of the adult brain to that of the entire body is approximately 1 150 (Ober- 

 steiner). In the new-born child this ratio is much greater, being, as determined by 

 Mies, i :5-9. Of the entire weight of the brain, the hemispheres contribute 78.5 per 

 cent., the brain-stem n per cent, and the cerebellum 10.5 percent., no material 

 difference being observed in the two sexes (Meynert). 



The extent of the superficial surface of the cortex has been determined, at least 

 approximately, by Wagner, who by completely covering the convolutions with gold 

 leaf concluded that the large brain of the mathematician Gauss (1492 gm. ) presented 

 an aggregate area of 221,000 sq. mm., or not quite one-half square meter. Of this 

 entire area about twin- as much lay along the sides and bottoms of the fissures, 

 therefore sunken, as upon the exposed surface. The estimate of the same observer 

 concerning the brain of a workman placed the area at 187,672 sq. mm. 



The significance of brain-weight as an index of intellectual capacity has long excited inter- 

 est. Accumulating data prove beyond question that, as applied to individuals, the weight of 

 the brain is an untrustworthy index of relative intelligence. For whilst in a number of conspic- 

 uous examples tin- \\ei-ht of the brains of men of acknowledged intellectual superiority has been 

 markedly above the average, it is equally true that some of the heaviest brains recorded have 

 been those of jwrsons of ordinary, and indeed in some cases of even decidedly inferior, intelli- 

 gence. Further, the brains of not a few men of remarkable achievement in the fields of Science, 



1 . \rchiv f. Anat. u. Kntwickelung., 1906. 



