Dog 



Monkey 



Pigeon 



Man 



THE BRAINS OF VERTEBRATES 



In birds the cerebellum is relatively larger than in mammals. In mammals there is an 

 increase in the amount of convolution, or wrinkling, of the brain cortex — the "bark" 

 of the cerebrum. The extent of the wrinkling is connected with the number of cells 

 and the complexity of their connections 



Living without a Brain^ You have no doubt heard of someone run- 

 ning around Hke a hen with her head chopped off. A bird or frog can 

 survive for days without using its brain. If the base of a frog's brain is cut 

 through, the animal will still move a hind leg so as to brush away anything 

 that touches the skin on that side. Many experiments show that animals can 

 carry out rather complex movements involving many parts of the body 

 when practically all the brain has been removed. 



We explain such brainless activities by the fact that nerve paths to the 

 effectors may be stimulated by processes outside the brain. These brainless 

 animals still lack something of being fully "alive". They never start any- 

 thing on their own initiative, not even taking food when it is placed right 

 before them. They will swallow food placed in the mouth, digest food, and 

 carry on other so-called "vital" functions. They will move away when 

 pushed, but will not dodge a threat. 



Such a brainless animal is indeed not strictly dead, but its living is largely 



iSee No. 3, p. 299. 

 281 



