386 



1) The passage of nerve fibres from undoubted neopallium into 

 the alveus of the dorsal hippocampus must be demonstrated. 2) It 

 must also be shown that these same fibres, after passing through the 

 alveus, actually pass into the dorsal commissure. 3) And even if 

 these two points can be demonstrated (which I believe to be im- 

 possible) it yet remains to be shown that these fibres really spring 

 from a wider cortical area than that which contributes to the formation 

 of the alveus of the ventral limb of the hippocampus : in other words, 

 that the questionable fibres have some right to be regarded as other 

 than fornix. 



In regard to the second element of proof (which is of fundamental 

 importance as a justification of Zuckerkandl's contention) no attempt 

 has been made to establish it as a fact. And, with reference to the 

 third element, the total result of Zuckerkandl's researches (compare 

 opera cit. N. la and c) is to demonstrate that both limbs of the dorsal 

 commissure in the Marsupialia present similar relations to the pallium 

 and that the ventral limb of the commissure in the Marsupial arises 

 in the same manner as the psalterium of the Eutheria: in other 

 words the dorsal commissure in the Marsupial is merely a two-limbed 

 psalterium or fornix -commissure. This, of course, is the view for 

 which Symington and I have been contending 5 ). 



The only evidence, which Zuckerkandl brings forward in support 

 of his statement that a true corpus callosum is present in the Mar- 

 supialia belongs to the first of the three essential categories enumer- 

 ated above. It is worthy of notice that Zuckerkanl bases his ob- 

 servations on the relation of the alveus to the corona radiata on a 

 series of horizontal sections: moreover his descriptions are chiefly, if 

 not wholly, concerned with the caudal parts of the dorsal limb (op. 

 cit. N. lc, p. 54 and 55, Fig. 1 and 2) and the ventral limb (p. 56 

 and 57, Fig. 3) of the hippocampus. In other words the major part 

 of his account deals with those parts of the hippocampal arc which 

 are quite unaffected by the development (and especially the early de- 

 velopment) of the corpus callosum. Moreover, horizontal sections such 

 as he represents [and also sagittal sections, such as I have figured 6 )] 

 exaggerate the extent of the apparently neopallial area from which 



5) Symington, The cerebral commissures in the Marsupialia and 

 Monotremata. Journ. of Anat. and Physiol., Vol. 27, 1893. — Elliot 

 Smith, opera cit. supra; also: Preliminary Communication on the Cere- 

 bral commissures. Proc. Linn. Soc. of New South Wales, 1894. 



6) The Fornix superior. Journ. of Anat. and Physiol., Vol. 31, 

 1896, Fig. 3, p. 86. 



