CORPUS STRIATUM OF MAMMALS 125 



logical patterns and functional specificity. On the 

 other hand, the pyriform cortex, as has already been 

 pointed out (p. 26), is always much more closely 

 related with the large and very ancient olfactory 

 reflex paths from the lateral olfactory nucleus, and 

 this cortex never attains the grade of structural dif- 

 ferentiation seen in the hippocampal and neopallial 

 fields. Moreover, in lower mammals within the pyri- 

 form lobe itself the complexity of cortical pattern is 

 progressively simplified as we pass from its posterior 

 end (which closely resembles neopallial cortex) to- 

 ward the olfactory bulb, and this simplification goes 

 hand-in-hand with increase in the number of fibers 

 received directly from the olfactory bulb through the 

 lateral olfactory tract (Herrick, 1924^). 



When these conditions of anatomical and physio- 

 logical detachment from the simpler reflex circuits 

 are fulfilled, differentiated cortex appears simultane- 

 ously in each of the several correlation centers so 

 related, and the intrinsic connections of these centers 

 among themselves permit types of association be- 

 tween the more elementary behavior patterns which 

 otherwise are impossible. In the simple cortex of 

 reptiles there is no clear-cut separation of projection 

 centers from association centers.^ The projection cen- 

 ters are foreshadowed in the pattern of subcortical 

 connections of the three separate cortical sheets, for 

 this pattern is different in hippocampus, general 

 cortex and pyriform lobe; but the associations appear 



