486 C. JUDSON HERRICK 



nuclei, it is probably the explanation of the great development of 

 the lateral nucleus in reptiles and lower mammals. The close 

 association of cells of the nucleus medianus septi with both the 

 anterior and posterior pallial commissures of reptiles, and the 

 migration of other elements upward into the fimbria as pars 

 fimbrialis septi of amphibians are doubtless similarly explained, 

 this being a case of neurobiotaxis (Kappers) or the movement of 

 cell bodies toward the source from which their stimulus is received. 

 Two other structures in this region of reptiles and lower mam- 

 mals require a word of comment. The corpus striatum extends 

 around the ventral border of the lateral ventricle into the median 

 wall to form the nucleus accumbens septi (see fig. 43 and Kappers, 

 '08). This is differentiated parallel with the tuberculum olfac- 

 torium farther ventrally. These two centers are both concerned 

 with the correlation of the medial and lateral elen ents of the 

 hemisphere. The tuberculum olfactorium puts the olfactory 

 bulb, septum and hippocampal cortex on the one hand into 

 relation with the striatum on the other hand, the olfactory 

 function predominating; the nucleus accumbens similarly puts 

 the septum into relation with the striatum with the striatal func- 

 tion dominant. 



THE MORPHOLOGY OF THE CEREBRAL CORTEX 



The simple natural subdivision of the cerebral hemisphere of 

 the frog summarized above (p. 478) is so evident anatomically as 

 to have been commented upon by all students of the subject. In 

 my opinion it gives the key to the functional interpretation, not 

 only of this brain, but of all higher brains. The four chief parts 

 of the hemisphere converge in front into the olfactory bulb. The 

 two ventral parts (pars subpallialis, Gaupp) connect directly with 

 the hypothalamus and pars ventralis thalami respectively. The 

 two dorsal parts (pars pallialis, Gaupp), though morphologically 

 related, as we have seen, to the pars dorsalis thalami and epi- 

 thalamus respectively, are cut off in forms above the fishes from 

 direct massive connection with the diencephalon by the di-telen- 

 cephalic fissure. Thus the dorsal parts, which originally belonged 



