164 BRAINS OF RATS AND MEN 



parable with that of primates is present, and prob- 

 ably motor and somesthetic cortical fields are at least 

 in part coextensive. 



The olfactory cortical fields of the archipallium of 

 the opossum and the rodents are easily compared, and 

 they are essentially similar except for the much larger 

 pyriform lobe and underlying amygdala in marsu- 

 pials. The remaining cortical areas are more variable 

 from species to species than are the projection centers 

 already considered, and it is not profitable in this con- 

 nection to review them comparatively. 



The cortical areas of the rabbit, mouse, and rat 

 have been charted independently by several investi- 

 gators.^ When the reports of their examinations of the 

 same species are compared the result is disquieting. 

 All agree that in these lowly forms the boundaries be- 

 tween the various areas are indefinite and that the 

 structural features by which the areas are distin- 

 guished are far less well defined than in higher brains. 

 It follows that any chart of the anatomical localiza- 

 tion within the cortex is necessarily more or less 

 arbitrary, and the number of areas recognized, as 

 well as their boundaries, will depend upon the cri- 

 teria employed, the acuity of observation, the ex- 

 perience and discriminative skill, and other subjective 

 factors of the several investigators. When it comes to 

 comparison of one species with another, the pitfalls 



^ Brodmann (1909), Dollken (1907), Fortuyn (1914), Isenschmid 

 (191 1), De Vries (191 1), Winkler and Potter (191 1). 



