385 



it seems desirable to once more categorically state the reasons for 

 this view. Many eminent anatomists, who have read the whole of the 

 literature relating to this much -discussed topic, still utterly fail to 

 appreciate the true nature of the point at issue; and misleading 

 statements are still common eveD in the most recent handbooks 3 ). 

 The importance of the subject is quite a sufficient justification for 

 calling attention once more to well-known evidence ; because the same 

 arguments which Zuckerkandl adduces might with equal justification 

 be applied to the cases presented by the Monotremata and the Reptilia. 



Perameles is the type adopted by Zuckerkandl (op. cit. N. lc) 

 as affording the clearest demonstration of "die Einstrahlung von 

 Palliumfasern in den Alveus" (p. 53). I have therefore adopted the 

 same genus to supply the evidence in refutation of his conclusions. 

 If a corpus callosum is present it must be sought at the anterior ex- 

 tremity of the commissura dorsalis 4 ). The accompanying figure re- 

 presents the connections of the fibres of the commissura dorsalis in 

 this crucial anterior region. In a previous work (op. cit., The Origin 

 of the Corpus callosum) I have described in detail the general topo- 

 graphy and minute structure of this part of the brain of Perameles. 



It is obvious at a glance that the vast majority of the fibres of 

 the dorsal commissure come from the hippocampus via the alveus; 

 and also that the bulk of the fibres coming from the neopallium pro- 

 ceed away from the hippocampus. Such of these neopallial 

 fibres as are destined to pass into the other cerebral hemisphere pro- 

 ceed from the corona radiata into the Capsula externa and thence into 

 the commissura ventralis. The problem to be determined thus resolves 

 itself into the question whether or not any fibres coming from the 

 neopallium pass into the commissura dorsalis via the alveus instead 

 of accompanying the vast majority of the commissural neopallial fibres 

 into the Capsula externa and the commissura ventralis. 



It is obvious that two, or perhaps even three, facts must be in- 

 dubitably established before the existence of a true alveus - invading 

 corpus callosum in Perameles can be admitted as proven. 



3) For example, see G-egenbaur, Vergleichende Anatomie der 

 Wirbelthiere, Bd. 1, 1898, p. 758, and Beddakd, Mammalia, London 

 1902, p. 126. 



4) Vide Zuckerkandl, opera cit. supra. Also my memoirs: The 

 Origin of the Corpus callosum. Transact, of the Linnean Soc. of London, 

 1897. — The Relation of the Fornix to the Margin of the Cerebral 

 Cortex. Journ. of Anat. and Physiol., Vol. 32. 



Anat. Anz. XXIII. Aufsätze. 25 



