NATUEAL SUBDIVISION OF THE CEREBRAL HEMISPHERE. 445 



have exposed in the above notes ; and Hochstetter ^ has recently 

 shown how fallacious must be the conclusions drawn from a 

 belief in the genuineness of " Bogenwindungen." 



Arguing from the comparative standpoint, I attempted in 

 1897 to expose the futility of such efforts,^ and this criticism 

 called forth an instructive rejoinder,^ to which the reader is 

 referred. 



It is now necessary to discuss the relationship which the 

 hippocampal formation presents to the main subdivisions of the 

 hemisphere. Both Turner and His exclude it from the rhinen- 

 cephalon, and, ipso facto, regard it as part of the pallium. 

 Schwalbe includes it in his falciform lobe. His includes part of 

 the paraterminal body (Broca's area and Zuckerkandl's gyrus 

 subcallosus) in the rhinencephalon, and excludes the rest 

 (septum lucidum), whereas Turner mentions none of these 

 bodies, and presumably includes them in his pallium. 



An examination of the brain in the Monotremata and the 

 lower Vertebrata shows that the paraterminal body is merely a 

 connecting link between the olfactory bulb and the hippocampus. 

 This body is intimately connected on the one side with the 

 hippocampus and on the other with the olfactory peduncle, into 

 which it merges anteriorly. A study of the progressive evolu- 

 tion of this region in the lowlier Vertebrates, and especially the 

 Amphibia, shows that the hippocampus and the paraterminal 

 body are essentially specialised parts of one ganglionic mass ; 

 and that the latter retains its primitive structure and its original 

 relations to the olfactory peduncle and bulb, and forms the 

 connecting link to the progressively-specialised hippocampus. 

 Therefore any method of subdividing the cerebral hemisphere 

 which ignores this interdependence and separates these two 

 histological formations must, ipso facto, be arbitrary and 

 vmnatural. 



Although these two structures appear to become separated 



1 F. Hochstetter, " Beitnige zur Entwick. d. Gehirns," Bibliotheca Mcdica, 

 Stuttgart, 1898. 



2 "The Relation of the Fornix to the Margin of the Cerebral Cortex," Joiu\ 

 of Anat. and Phi/s., vol. x\xii. pp. 56-57. 



^ G. Retzius, " Zur Morphologie der Fascia Dentata und Hirer Uingebungeri," 

 Biologisch. Untersuchungen, Bd. viii., 1898, No. 3. Compare also "Zur Aus- 

 seren Morphologie des Riechhirns," etc. Op. cit., No. 2, p. 25, regarding the 

 terms ^' pallium" a.n<\. ^'rhinencephalon.^' 



