640 CEREBRAL COMMISSURES OF THE MAMMALIA, 



may be remarked, however, in passing, that Hill's statement* 

 that "all such fornix as exists in Orniihorliynchus crosses in the 

 middle line " and that the descending fornix fibres come from the 

 hippocampal commissure is absolutely erroneous, since the great 

 majority of such fibres come directly from the alveus and never 

 cross the middle line. His further description of their destination 

 and of the formation of the taenia thalami is equally inaccurate. 



On separating the cerebral hemispheres of any Marsupial or 

 Monotreme from above, a large white transverse band will be 

 noticed passing between the two hemispheres and hiding from 

 view the anterior extremity of the third ventricle and the 

 foramina of Monro. The question of the homology of this band 

 has been the subject of much controversy. 



A full account of the earlier discussion of this question will be 

 found in the paper of Flower,! and the more recent bibliography 

 will be found in the papers of Symingtonl and Hill.§ Ever 

 since Meckel's monograph] | there have been supporters of his view 

 that the superior commissure was corpus callosum. Thus Flower 

 in Echidna and a series of Marsupials,11 Pappenheim in Didelphis,*'^ 

 Sander in Macr ojms a.nd Didelphis,-\j Osborn in ftetal Macropus,ll 

 Zuckerkandl in Platypus, §§ and Herrick in IJideljjhiSyWW ^s well 

 .as in numerous papers elsewhere, have, among others, supported 



* Loc. cit. 



t " On the Commissures of the Cerebral Hemispheres of the Marsupialia 

 and Monotremata," Phil. Trans. 1865, p. 633. 



X " The Cerebral Commissures in the Mammalia and Monotremata," 

 Journ. of Anat. Vol. xxvii. p. 69. 



§ "Cerebrum of Ornithorhynchus," Phil. Trans. B. 1893. 

 il Descr. Anat. Ornithor. parodoxi, 1827. 



H Loc. cit. 

 ** Compt. Kendus, Vol. xxiv. p. 186, 1847. 

 tt " Ueber das Quercommissurensystem des Gehirns bei den Beutel- 

 thieren," Arch. f. Anat. 1868. 



t+ "The Origin of the Corpus Callosum," Morph. Jahrbuch, Vol. xii. 



§§ " Ueber des Riechcentrum," 1887. 

 nil " Callosum and Hippocampus in Marsupial and lower brains," Journ. 

 of Comp. Neurology, Vol. iii. p. 179. 



