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cal hippocampus, nor, on the other hand, are they grouped in 

 the manner characteristic of the neopallium. The region is in fact 

 really transitional and, so far as its structure is concerned, might 

 be included in either the hippocampus or the neopallium. This 

 transition-region is found fringing the hippocampus in the whole of 

 its extent, not only in the Marsupial brain but in that of all mam- 

 mals 7 ). The fact that the fibres from this transition - region behave 

 like those of the hippocampus (i. e. pass into the alveus) seems to 

 indicate (in the absence of any reason for the contrary opinion) that 

 it (the region x) really belongs to and forms a part of the hippo- 

 campus. The most careful examination of the whole region in the 

 neighbourhood of the hippocampo - neopallial junction in the critical 

 area (i. e. the area where the primitive corpus callosum might be ex- 

 pected) has failed to reveal any fibres proceeding from the undoubted 

 neopallium (beyond this transition-region) into the alveus. 



Moreover in specimens stained by the GoLGi-method I have been 

 unable to find any fibres coming even from the region x which extend 

 so far as the dorsal commissure. 



So far as the evidence at my disposal enables me to express an 

 opinion on this subject, lam utterly unable to find any trace 

 of a neopallial commissural bundle (i. e. a corpus callo- 

 sum) traversing the alveus to reach the dorsal com- 

 missure in Perameles or any other Marsupial. On the contrary 

 the most careful examination amply demonstrates that the root-fibres 

 of the dorsal commissure exhibit the same relation to the cortex as 

 the fornix does in all mammals. Even Zuckerkandl, if I read his 

 memoirs aright, subscribes to this opinion. He cannot therefore ob- 

 ject to the application of the term "fornix - commissure" to the whole 

 of the dorsal commissure in the Marsupialia, seeing that this name is 

 applied to the mammalian psalterium. But if he calls the dorsal com- 

 missure of the Marsupial the "corpus callosum", he ought, if he be 

 logical, to call the psalterium of other mammals "corpus callosum" 

 also. In other words there is no more justification for regarding the 

 dorsal commissure of Marsupials as including neopallial elements than 

 there is for considering the psalterium to be a mixture of hippo- 

 campal and neopallial fibres. 



Although the corpus callosum (in the form of a neopallial 



7) Compare Koelliker's Handbuch der Gewebelehre des Menschen, 

 Bd. 2, 6. Aufl., 1896, Fig. 785 (p. 754) representing a section through 

 the hippocampus of Lepus. 



