166 A MANUAL OF ANATOMY. 



At the base exercise the greatest caution, so as to leave behind the cranial 

 nerves and the other important structures there. About the nerves it may be 

 well to leave the pia, as they usually are torn off with it. 



Anteriorly the lamina cinerea will be torn through if any force is attempted 

 in taking up the pia. Do not attempt in any place to remove the blood-ves- 

 sels entire, but with the scissors clip them wherever there is any resistance 

 and turn to another place close by to continue their removal. 



The Brain. Figs. 23, 29. 



The brain is all that part of the cerebrospinal system 

 contained within the cranial cavity. It varies in weight 

 according to sex, age, race, and intelligence (see qualifica- 

 tions later). At birth the brain bears a larger proportion to 

 the body weight than at any later time ; it is for males as 

 I : 5.85, and for females as I : 6. 5. The brain grows very 

 fast up to the seventh year, but not so fast as the body 

 weight increases, the ratio being brain to body as I : 1 3 or 

 14. The increase is more slowly up to the. twentieth year, 

 when the ratio to the body is as I : 30. From thirty to 

 forty the brain grows very slowly, reaching its maximum 

 weight between forty and fifty years of age. After the 

 maximum is reached the brain begins to lose weight very 

 slowly, at the rate of about an ounce for every ten years of 

 life. 



The ratio of the cerebrum to the cerebellum is 8^- : I 

 for males, and 8^ : I for females. 



Race. The largest brains belong to the civilized races, 

 Europeans (English, Germans, Scotch, etc.) and the 

 Chinese. The smallest to the savage races, as the native 

 Africans and Australians. 



Intelligence. While there is some ratio between the 

 degree of intelligence and the brain weight, it is at most 

 very unreliable for comparison between individuals of the 

 same race. As Dana states ("Text Book of Nervous 

 Diseases "), among 100 intelligent persons the proportion of 



