450 C. JUDSON HERRICK 



The details of this dramatic history cannot be recounted here. 

 In a general view of the process it may be said that in cyclostomes 

 the entire endbrain and a large part of the betweenbrain are 

 dominated by the olfactory system, the non-olfactory components 

 entering this territory from the midbrain being relatively small 

 and incompletely known. As we ascend the vertebrate scale 

 the non-olfactory systems assume progressively greater impor- 

 tance. In urodeles a considerable part of the thalamus is 

 devoted exclusively to non-olfactory correlations, but no part 

 of the cerebral hemispheres is wholly free from olfactory con- 

 nections. In reptiles the ascending systems are greatly enlarged 

 and a portion of the corpus striatum complex appears to be 

 devoted exclusively to them. Here there is well-defined cerebral 

 cortex, most of which is clearly dominated by its olfactory con- 

 nections (hippocampus and pyriform lobe), though in another 

 part (the general cortex) somatic systems predominate (Elliot 

 Smith, '10, '19). In mammals somatic systems with no admix- 

 ture of olfactory elements come to dominate the architecture 

 and functions of the cerebral hemispheres, until in man, whose 

 olfactory organs are greatly reduced, the olfactory centers are 

 crowded down into relatively obscure crannies of the hemisphere 

 by the overgrown somatic systems. 



CONCLUSION 



In summary, it may be regarded as established that the 

 terminal portion of the neural tube early in vertebrate evolution 

 gave rise to two pairs of lateral evaginations in correlation with 

 the differentiation of the two sense organs which serve as the 

 most important distance receptors, namely, the optic vesicles 

 and the olfactory bulbs. In the most primitive living verte- 

 brates almost all of the brain in front of the midbrain is dominated 

 by the olfactory system and the differentiation of this region in 

 all higher forms appears to have taken place largely under the 

 influence of various systems of non-olfactory fibers which have 

 grown forward into this olfactory territory. Increasingly com- 

 plex correlations of the various other senses with smell have 



