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Show 192 MR. W. A. FORBES ON THE KOALA. [Jan. 18» deep, strongly curved, and continued forwards over the corpus callosum onto'the internal face of the hemispheres to a point about 0-15 inch in front of the anterior commissure. Behind is another rather deep,/-shaped sulcus, which appears at both ends on the prominent rounded margin of the hemispheres. ^ The corpus fim-briatum and fascia dentata are both distinct. The middle (grey) commissure is very large. Of the corpora quadrigemina, the nates are longer (from before backwards) than the testes. The posterior limb of the crucial impression is not as distinct as the fore one. In the cerebellum the vermis is well-developed, as are the lateral lobes and the flocculi, which have the form of projecting, rounded lobes. The pons Varolii is narrow, the anterior pyramids well-defined, and the corpora trapezoidea distinct. As compared with Phascolomys, the principal points of difference in the brain are the more richly convoluted hemispheres-a distinct calloso-marginaI sulcus being present, as well as others on the external surface-and the non-projectingyfoccwft, of the latter. Phalangista has nearly as simple a brain as the Koala; but the flocculi project more. A consideration of some of the facts on the visceral anatomy of the Koala here stated appears to me to throw considerable light on the classification of the Marsupials. Naturalists generally have placed the Koala in, or close to, the Phalangistidae ; whilst the Wombats have been retained as a separate family or section, of equal value with the former group, the Kangaroos being often, indeed, interposed between the two1. Writing as long ago as 1846, Mr. G. R. Waterhouse, in his 'Natural History of the Mammalia' (vol. i.), though in that work keeping the Phascolomyidae separate from the Phalangistidae, evidently did so with some hesitation. He says (/. c. p. 16) : - " Upon a careful examination of the Wombat, I find so many points in common with the Phalangista group, that it is so intimately connected with the Koala (which is more clearly an aberrant Phalanger), as indicated by the structure of the stomach and the deficiency in the number of the false molars, and the total absence of tail, that I am inclined to regard the genus Phascolomys as presenting an aberrant form only of the Phalangistidae. That the thumb should be reduced to a small size in this animal, which differs from others of its (supposed) family in living upon the ground, I am prepared for, since in the Dasyuridae the same thing takes place under similar circumstances. I am also prepared to find in an herbivorous group like the Phalangistidae a difference in the structure of the molar teeth, in having them rooted in one case and rootless in another, for such happens in other herbivorous groups of the Mammalia." Again, in a note on p. 257 : - " With regard to the position of the Wombat and the Koala (Phascolarclus) in a natural system, I may observe, in the first place, the Wombat (ca?teris paribus) shows some affinity to the Phalangistidae in the possession of a thumb, which, though short, is very broad and sufficiently distinct. Then, beyond this, we have to add that the 1 Cf Owen, " Classification of the Marsupialia," P. Z. S. 1839, p. 19 ; Sclater, Rev. List of Vertebrata, 7th edition, 1879. |