ORIGINS OF THE CEREBRAL CORTEX 71 



THE ICHTHYOPSID TYPE 



In fishes and amphibians the cortical primordia 

 are reflex centers which do not differ in principle from 



olfactorq N^ 

 bulb 



endbroin 



cptic nerve 



between brain 



midbrain 



nosebrain 



meduilQ 

 oblongat 



spinal cord 



Fig. 6. — Brain of the dogfish, Squalus acanthlas, natural size. The 

 olfactory field, or nosebrain, is marked with coarse dots, the eyebrain 

 with crosses, the earbrain with oblique cross-hatching, the skinbrain with 

 vertical hatching, the tastebrain with horizontal hatching. The mem- 

 branous roof of the fourth ventricle has been removed. 



those of the rest of the brain stem. The brain of the 

 common marine dogfish (a small shark) is illustrated 

 in Figure 6. Its most striking feature from our stand- 



