Herrick, Subdivision of the Brain. 407 



the third order are treated as palHum. The apphcation of this 

 principle, however, proves to be very difficult, for there are many 

 cases where olfactory tracts of the third order run to basal regions 

 which have none of the other characteristics of pallium, and on the 

 other hand the archipallium (hippocampus) of all higher verte- 

 brates, including man, is said on good authority to receive olfac- 

 tory fibers of the second order, as well as of higher orders. 



It is clear that in mammals the distinction between hyposphae- 

 rium and episphaerium is capable of tolerably precise anatomical 

 definition and is easily recognized. While accepting this as an 

 important anatomical fact, the writer is of the opinion that our 

 knowledge of both the histology and the phylogeny of the mam- 

 malian pallium is still too imperfect to permit of its final mor- 

 phological interpretation. The phylogeny of the pallium is 

 now under active investigation in a number of important neuro- 

 logical laboratories and until our knowledge of its early phylo- 

 genetic stages is more complete it is better to avoid dogmatism 

 and await fuller knowledge before attempting to elaborate in 

 detail the morphology of the telencephalon. The unsettled state 

 of opinion regarding the fundamental character of cerebral local- 

 ization further emphasizes the need of caution in fortbrain 

 morphology. 



We may, then, summarize our scheme of subdivision of the 

 vertebrate nervous system as follows:"^ 



Systema nervorum sympathicum (BNA). 

 Systema nervorum cerebro-spinale. 

 Systema nervorum periphericum (BNA). 

 Systema nervorum centrale (BNA). 



Medulla spinalis (BNA). 



Encephalon (BNA). 



Rhombencephalon (BNA). 



'" It should be borne in mind that the terms adopted in this table are not coordinate in morpholog- 

 ical value from any standpoint. They are offered simply as a practicable suggestion for a terminology 

 which shall be available for all vertebrates and which deviates as little as possible from the most widely 

 used standard of our time. 



The writer would add, moreover, that in recommending this subdivision and nomenclature he by no 

 means pleads for its final adoption as a whole. This scheme is manifestly defective in many places, and 

 it is hoped and expected that further discussion will clarify the more obscure points. These pages are 

 offered primarily as a contribution to method and it is earnestly maintained that the principles here 

 illustrated are vitally important and must be taken into account in all future morphological work in this 

 field. The exact limits of the regions and the names to be applied to them are subsidiary considerations 

 upon which unanimity of opinion can hardly be expected until our anatomical and physiological knowl- 

 edge is far more complete. 



