74 



BRAINS OF RATS AND MEN 



animals. The dorsolateral sector (primordial pyriform 

 lobe) shows no tendency toward cortical formation, 

 but the cells of the dorsomedial sector (primordial 

 hippocampus) have begun to move away from the 



pijriform 

 lobe 



ppocompus 



septum 



Fig. 9. — Cross-section through the left cerebral hemisphere of the 

 frog to illustrate the arrangement of nerve cells in the different sectors. 

 The parts above the line A-B axe. regarded as regions within which cortex 

 appears in higher vertebrates. Redrawn from Johnston, 



ventricular surface and are uniformly distributed 

 throughout the thickness of the wall. This is a tend- 

 ency toward cortical arrangement though it cannot 

 be called true cortex. 



We have little evidence that the reflex functions 

 of the forebrain of fishes differ in principle from those 

 of the midbrain and medulla oblongata, though the 



