The Nervous System 



322. Weight of the Brain. The 



average weight of the adult human 

 brain is about fifty ounces for men 

 and forty-five ounces for women. 

 Other things being equal, the size 

 and weight of the brain bear a general 

 relation to the mental power of the 

 individual. As a rule, a large, healthy 

 brain stands for a vigorous and supe- 

 rior intellect. 



The brains of many eminent men 

 have been found to be eight to twelve 

 ounces above the average weight, but 

 there are notable exceptions. The 

 brains of idiots are usually small and 

 badly developed. The brain and head 

 of a child are very large in proportion 

 to the rest of the body. 

 *323, The Cerebrum. The three 

 principal masses which make up the 



brain when .viewed as a whole are : 

 ,/ 



1. The cerebrum, or brain proper. 



2. The cerebellum, or lesser brain. 



3. The medulla oblongata. 



The cerebrum comprises nearly 

 seven-eighths of the entire mass and 

 fills the upper part of the skull. It 

 consists of two halves, the right and 

 left cerebral hemispheres. These are 

 almost separated from each other by 

 a deep median fissure. Each of the 

 hemispheres is subdivided into three 



21 I 



FIG. 115. Diagram of a 



Motor Nerve Cell. 

 (Showing its long, unbranched 

 process (with two little lateral 

 offshoots), with motor endings 

 in striated, voluntary muscle 

 tissue. By comparison with 

 Figs. 113 and 114 the several 

 unmarked parts in this dia- 

 gram may be readily under- 

 stood.) 



