OP THE MAESUPI ALI A AND MONOTEEMATA. 
641 
corpus callosum; but this determination does not invalidate the fact that the great 
commissure which unites the supraventricular masses of the hemispheres in the Beaver 
and all other placentally developed Mammalia, and which exists in addition to the 
hippocampal commissure, is wanting in the brain of the Wombat: and as the same 
deficiency exists in the brain of the Great and Bush Kangaroos, the Vulpine Phalanger, 
the Ursine, and Mauge’s Dasyures, and the Virginian Opossum, it is most probably the 
characteristic of the marsupial division of Mammalia.” The relatively large size of the 
anterior commissure in the marsupials is referred to in the paper as worthy of notice, 
as also is the proportionally very large size of the hippocampi majores. 
The description given in this important memoir was subsequently reproduced in the 
Cyclopaedia of Anatomy and Physiology, art. Marsupialia, and it was shown that the 
same peculiarity also existed in the Monotremata, and therefore was characteristic of the 
whole implacental division. In the paper by the same author “ On the Characters, 
Principles of Division and Primary Groups of the Class Mammalia”*, the Subclass 
Ly encephala (“ loose” or “ disconnected” brain), equivalent to the Implacentalia, are 
characterized as having “ the cerebral hemispheres but feebly and partially connected 
together by the ‘ fornix’ and 4 anterior commissure,’ while in the rest of the class a part 
called ‘corpus callosum’ is added, which completes the connecting or commissural 
apparatus’^. The views of Professor Owen have been adopted without hesitation or 
qualification, in this country at least, and have been incorporated in almost every text- 
book on Anatomy and Physiology subsequently published. The same has been the case 
to a great extent upon the continent, and what is more important, they have received 
confirmation apparently from original dissections of several of the marsupials by the 
editors of the third edition of Cuvier’s ‘ Anatomie Comparee,’ MM. F. Cuvier and 
Laurillard (1844), and in the case of the Echidna by MM. Eydout and Laurent 
(Voyage de la Favorite, 1839). 
But expressions of dissent have also been raised. Leuret, speaking of the brain of 
* Proc. Linn. Soc. 1858. 
t [The necessity of doing full justice to the labours of one who has made this subject so peculiarly his own, 
will excuse my quoting the following succinct account of the distinctive characteristics of the views of this 
eminent anatomist, as set forth in his most recent publication bearing upon the question. 
“ In investigating and studying the value and application of the cerebral characters of Man in the classifica- 
tion of the Mammalia, I have been led to note the relations of equivalent modifications of cerebral structure to 
the extent of the groups of mammals respectively characterized by such conditions of brain. The Monotremes 
and Marsupials, which offer numerous extreme modifications of the limbs, all agree in possessing a brain in 
which there is no connecting or commissural mass of fibres overarching the lateral ventricles of the cerebrum. 
The surface of this part shows, however, a few symmetrical convolutions in Echidna and Macropus, especially 
the largest species ; but in the majority of marsupials the hemispheres are smooth. The £ corpus callosum,’ or 
great commissure, makes its appearance abruptly in the Eats, Shrews, Bats, and Sloths, which in general 
organization and powers are next the ‘ loose-brained ’ marsupials or Ly encephala : but this commissure is 
associated with a similarly smooth unconvolute cerebrum, and with so small a size of the cerebrum as leaves 
uncovered the cerebellum and in most the optic lobes.” — Contributions to the Natural History of the 
Anthropoid Apes, No. VIII., by Professor Owen, Trans. Zool. Soc. vol. v. part 4, 1865, p. 270. — April 1865.] 
MDCCCLXV. 4 T 
