CORTEX AND CORPUS STRIATUM 93 



mentally have so far yielded meager and confusing 

 results. Most of the behavior of lower vertebrates is 

 not plastic but stereotyped — either innate or habitual 

 — and the laboratory experiments so far devised have 

 not revealed all that we need to know regarding the 

 relations of the cerebral cortex to behavior patterns. 

 In fact, we have very little adequately controlled 

 knowledge of the details of the behavior of lower 

 vertebrates except in connection with sense physi- 

 ology and trial-and-error learning. To this subject 

 we shall return. 



The beginnings of the corpus striatum can be 

 recognized in fishes and amphibians, though very in- 

 completely separated from adjoining parts of the fore- 

 brain. In all reptiles the corpus striatum complex is 

 greatly enlarged and complicated. In birds it is still 

 larger and more complex, more so than in any other 

 vertebrates. In view of the deficiency of cerebral 

 cortex in birds, these are the most favorable species 

 in which to study the functions of the corpus striatum 

 itself. 



BIRDS 



For a century past the behavior of birds with 

 cerebral hemispheres injured or destroyed has been 

 assiduously studied. Upon complete removal of the 

 hemispheres the bird is in a state of idiocy, but if 

 the thalamus is undisturbed there is little change in 

 the simpler reflexes. The animal at times stands 



