CORTEX AND CORPUS STRIATUM loi 



a broader connection between the thalamus and the 

 hemisphere. This means in terms of behavior that 

 reptiles make far more efficient use of their extero- 

 ceptive sense organs than do fishes or amphibians; 

 they are more adaptable to changes in their environ- 

 ments. These adaptations are mostly effected by 

 relatively fixed reflex, instinctive, and habitual be- 

 havior, but not wholly so. 



In turtles the greatly thickened lateral wall of the 

 cerebral hemisphere contains three structures which 

 are intimately related, corpus striatum, amygdala, 

 and pyriform cortex. The first two are subcortical 

 structures. The pyriform cortex clothes the amygdala 

 and seems to have differentiated out of it, at least in 

 part. The general cortex of reptiles (forerunner of 

 mammalian neopallium) is similarly related to the 

 non-olfactory part of the corpus striatum. The analy- 

 sis of the reptilian strio-amygdaloid complex must 

 therefore precede a complete understanding of the 

 rise of the cerebral cortex. 



The brains of reptiles have been intensively 

 studied by several competent neurologists and the 

 analysis of their cerebral hemispheres is well ad- 

 vanced. The following discussion (pp. io2~iii) must 

 necessarily include some technical details which may 

 not be of interest to all readers. To such the friendly 

 hint may be given that the omission of these pages will 

 not seriously impair the continuity of the remainder 

 of the text. 



