THE CEREBRAL HEMISPHERES 



56 7 



taken as the average limits. In females the minimum was 31 ounces 

 (878.8 grams), and the maximum, 56 ounces (1587.6 grams). In 125 

 cases out of the 191, the weights ranged between 41 and 47 ounces 

 (1162.3 and 1332.4 grams). 



Quain assumed, from various researches, that in new-born infants 

 the brain weighs 11.65 ounces (327.8 grams), for the m^le, and 10 

 ounces (283.5 g ram s), for the female. In both sexes, "the weight of 

 the brain generally increases rapidly up to the seventh year, then more 

 slowly to between sixteen and twenty, and again more slowly to between 

 thirty-one and forty, at which time it reaches its maximum point. Beyond 

 that period, there appears a slow but progressive diminution in weight 

 of about one ounce (28.3 grams) during each subsequent decennial period ; 

 thus confirming the opinion, that the brain diminishes in advanced life." 



The comparative weights of the several parts of the encephalon, 

 calculated by Reid from observations on the brains of fifty-three males 

 and thirty-four females, between the ages of twenty-five and fifty-five, are 

 as follows : 



' The proportionate weight of the cerebellum to that of the cerebrum, 

 in the male, is as I to 8|, and in the female, as I to 8| (Quain). 



The specific gravity of the whole encephalon is about 1036, that of 

 the gray matter being 1034, and of the white, 1040 (Quain). 



THE CEREBRAL HEMISPHERES 



Cortical Substance. The surface of the cerebral hemispheres is 

 marked with fissures, sulci and convolutions, which serve to increase 

 the extent of the gray substance. The sulci between the convolutions 

 vary in depth in different parts, the average being about an inch (25.4 

 millimeters). The gray matter, which is external and follows the con- 

 volutions, is -|- to \ of an inch (2.1 to 3.2 millimeters) in thickness. 

 Anatomists have described this substance as existing in several layers, 

 but these divisions are largely artificial. In certain parts, however, par- 

 ticularly in the posterior portion of the cerebrum, the gray substance 



