THE SEAT OF INTELLIGENCE. 



285 



brain, and is composed mainly of blood vessels which run down 

 into the brain matter. 



The right side of the brain supplies the left side of the body 

 with nerves, and vice versa. This is why an injury to the motor 

 centres of the right side of the brain will paralyse the body on the 

 opposite side. 



The Seat of Intelligence 

 When all the membranes covering the brain are removed, its 

 surface is seen to be covered with deep depressions. This is due 



Fig. 116. — Section of the human brain showing one hemisphere of the Cere- 

 brum and Cerebellum. The part on the right is the forehead portion. 

 Note the foldings or convolutions. (From Blackie's Physiology.) 



to the foldings of the outer layers of brain matter. These foldings 

 are known as convolutions. The object of these depressions and 

 foldings is to provide as large a surface as possible, without unduly 

 enlarging the brain and skull. This extensive surface is covered 

 with a layer of nerve cells of a greyish colour. The thickness of 

 the grey matter is determined by the degree of mental evolution 

 of the individual. This layer of microscopically small cells of a 

 greyish colour, which is usually only about the eighth of an inch 

 thick, gives rise to every thought, every desire, and every emotion 



