PROBLEM 2. Why Co?f/pIex Behavior Is FossihJc 



273 



Fish Amphibian Reptile Bird Mammal 



(Trouf) (Frog) (Alligafor) (Sparrow) (Dog) 



Fig. 257 Which parts do you find in all five brains? Which part is not visible in the 

 dog's brain? Is there any siinilarity in the general plan of these brains? Compare the 

 dog's brai7i with that of the sheep shown in Figure 2^5. 



man, is evidently a very busy portion of 

 the brain. 



Activities of the cerebellum and me- 

 dulla. If both cerebrum and cerebellum 

 are removed, the pigeon can still move 

 the muscles of its legs and wings but per- 

 fect control of these parts seems to have 

 been lost. The bird stumbles and staggers 

 and falls over on its side. Each muscle 

 can contract but it can no longer work 

 in cooperation with the others. This and 

 similar experiments provide evidence 

 that the cerebellum is needed for proper 

 teamwork or coordtnatio?}, as it is called, 

 between the muscles of the body. With- 

 out the cerebellum the animal cannot be- 

 have as a unit. Since there are more than 

 two hundred muscles in a vertebrate's 

 body, the coordinating of muscular 

 movements is important. 



But even in the absence of a cerebel- 

 lum the pigeon can continue to live if it 



is fed and protected. Its heart beats regu- 

 larly, it breathes, it still digests its food, 

 and if you touch its foot it still responds 

 by contractingr the muscles of the leg. 

 Evidently neither cerebrum nor cerebel- 

 lum controls these activities. But when 

 now the lowest portion of the brain, the 

 medulla, is removed, the results are dif- 

 ferent. The heart stops beating, breath- 

 ing ceases, and the pigeon dies. There 

 can be little doubt that circulation, 

 breathing, and other internal activities 

 depend on the medulla. 



The brains of other animals. While 

 experimentation with birds gives us con- 

 siderable insight into brain activities you 

 must not get the impression that the 

 bird's brain is just like man's brain in 

 structure. Study Figure 257 in which 

 there are drawings of the brain of a fish, 

 a frog, an alligator, a sparrow, and a dog. 

 These animals represent the five classes 



