THE BRAIN 



183 



the hemispheres of the brain. Its grey matter occupies the 

 interior. 



We have noticed that the functions of the cerebrum and the 

 cerebellum are not of vital importance, so that death does not 

 instantly follow the removal or destruction of these parts of the 

 brain. But the functions of the medulla oblongata are of such 

 a nature that instant death is the result of its destruction. It 

 governs those involuntary movements which constitute the acts of 



Fig. 1 68. The Under Surface of the Brain, showing the Origins of 

 the Twelve Pairs of Nerves. 



A, cerebrum ; B, cerebellum ; c, medulla oblongata ; D, pons Varolii. The Roman 

 numerals distinguish certain of the cranial nerves. 



breathing and swallowing. Hence, when it is destroyed the 

 breathing instantly ceases. It is the only means of communication 

 between the brain and the cord, and is therefore important as a 

 conducting medium. It also possesses properties similar to those 

 of the spinal cord, which will be explained in our next lesson. 



From the under surface of the brain twelve pairs of nerves are given off. 

 These are called the cranial nerves, and are numbered from before backwards. 



