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 
Fic. 114.—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 
