THE EVOLUTION OF THE BIRD 



rhe wrist into a single element and a corresponding fusion of 

 the two bones of the forearm. 



But the adoption of a life in the air not only requires a 

 modification of the physical structure of the wings and body 

 but affects the relative importance and even the character 

 of the senses as well as of the brain that makes use of the 

 information they afford. The sense of smell becomes much 

 less useful to a flying animal than it was to a crawling ani- 

 mal, which carries its head so close to the ground that it 

 can recognise the presence of other animals by the odours 

 which they leave behind them. We therefore find that the 

 nose of a bird — its sense of smell — is in no way better than 

 that of a crocodile. 



In order to utilize fully the improved senses and to adjust 

 them delicately to the conditions on which flight depends 

 modifications must be made in the structure of the brain. 

 The brain of a bird consists of the same parts as that of a 

 crocodile and resembles it very closely in its fundamental 

 arrangement, but that part (the cerebellum) which coordi- 

 nates the muscular movements and adjusts them to the con- 

 ditions under which the bird finds itself is much larger and 

 is more complicated in structure. The part of the brain that 

 is concerned with vision is larger, and the part that is con- 

 cerned with smell is smaller. 



More important in some respects is an enlargement of the 

 front part of the brain to enable the bird to bring together 

 there all the information that comes to it from its senses and 

 to decide on its behaviour in the light of the memories of 

 past events that are stored there. It is to the development 

 of this part of their brains that birds owe all those compe- 

 tencies in building their nests and in caring for and pro- 

 tecting their young which have long endeared them to 

 moralists. 



[249] 



