490 C. JUDSON HEERICK 



In this last point I presume Elliot Smith would concur, for in 

 discussing the rudimentary cerebral cortex which occurs in dip- 

 noans he remarks ('08, p. 529), "How much of the pallial formation 

 in Lepidosiren is hippocampus and how much is pyriform lobe 

 or whether, as in the Mammalia, there is any representative of 

 the neopallium interposed between them are all questions which 

 it is impossible to answer. We ought rather to look upon the pal- 

 lium of Lepidosiren as an area, which is yet unspecialized, the 

 rudiment of that more extensive cortical field which in the Mam- 

 malia becomes differentiated into distinct formations." Cf. also 

 his discussion, 1910. The non-olfactory associations of the 

 hippocampus are clearly of great importance even in the mammals, 

 as is proved by the fact that in anosmatic animals, such as 

 the Cetacea, the hippocampus is still extensively and typically 

 developed save for the absence or extreme reduction of its fascia 

 dentata (Hill, '93; Zuckerkandl, '87). 



We have as yet no satisfactory definition of cerebral cortex 

 and possibly the attempt to formulate such a definition at this 

 time is premature. 



Several recent writers (Johnston, Kappers, Edinger) have at- 

 tempted to define the cortex hippocampi exclusively in terms of 

 its relation to the olfactory system, viz., as a tertiary olfactory 

 center. But this is a quite insufficient criterion. Johnston in 

 his last contribution to the subject ('09) has emphasized some of 

 these objections and shown that the cerebral cortex, like the 

 other suprasegmental mechanisms, is essentially an organ of 

 correlation. Now, the path of conduction for afferent impulses 

 of a single type may have as many synapses interpolated and as 

 many avenues of collateral discharge as you please, without 

 thereby necessarily itself acquiring any significance as a center of 

 correlation. The fundamental architectural motive underlying 

 the evolution of the cerebral cortex is the demand for a center 

 into which two or more different afferent types may meet and dis- 

 charge into a single common final path. Of couse, this is not 

 an exclusive property of the cerebral cortex. What I mean to 

 say is that it is this type of subcortical correlation center which 

 has been elaborated to form the cortex. 



