446 PKOFESSOK G. ELLIOT SMITH. 



the one from the other in the Eutheria, they are still closely 

 linked together, not only by the fornix and septum lucidum, 

 but also by the vestiges of the anterior part of the hippocampal 

 arc, which remain as a testimony to the intimacy of the 

 relationship between these two bodies. If physiological reasons 

 had any weight in this argument, the hippocampus should, 

 beyond all question, be regarded as part of the rhinencephalon 

 or "smell-brain," But the question at issue is not a problem 

 of function, but one that must be settled upon purely morpho- 

 logical grounds. The relations which a study of the brain in 

 the Sauropsida and Monotremata shows to exist between the 

 olfactory peduncle, the corpus paraterminale, and the hippo- 

 campus, establish a claim for the two latter bodies at least equal 

 to that of the pyriform lobe and tuberculum olfactorium in the 

 constitution of a rhinencephalon. The point at issue is this : — 

 that the term " rhinencephalon " can logically be applied only to 

 the olfactory bulb and its peduncle (i.e., in its original applica- 

 tion by Owen), or it should also include all those specially 

 modified parts of the cerebral hemisphere the fate of which is 

 linked inseparably with that of the olfactory bulb. If the latter 

 course is followed, we must include the whole pyriform lobe, as 

 well as the paraterminal body and the whole hippocampal 

 formation. For if we exclude the latter, where can we ration- 

 ally draw the line between the hippocampus and the olfactory 

 peduncle ? Even His and the German Nomenclature Commis- 

 sion include the gyrus subcallosus, i.e., part of the paraterminal 

 body. But to be logical we must also include the rest of this 

 body, i.e., the septum lucidum. And we cannot draw the line of 

 division between the paraterminal body and the hippocampus, 

 between two structures the fate of each of which is so intimately 

 bound up in that of the other.'^ 



Upon these grounds alone, even if there were no other reasons,, 

 the hippocampus has an unquestionable right to be grouped 

 along with the paraterminal body and olfactory apparatus in the 

 " smell-brain," whether we call such a complex " rhinencephalon" 

 or not. But there are more potent reasons than these for such 

 a grouping. 



^ For f'uitlier information concerniiif^ the intimacy of the connections of these 

 bodies see " The Relation of the Fornix," etc., this Journal, vol. xxxii. 



