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 

 0-1.5 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 Jim- 

 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 Phascolomijs, the principal points of difference 

 in the brain are the more richly convoluted hemispheres — a distinct 

 calloso-marginal sulcus being present, as well as others on the external 

 surface — and the non-projecting/ocfw/z, of the latter. Phalangista 

 has nearly as simple a brain as the Koala; but the Jlocculi 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 Phalangistidse ; 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 two\ 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 Phascolomyidce separate 

 from the Phalangistidte, evidently did so with some hesitation. He 

 says (I. c. p. Ki) : — " 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 Phalangistidse. 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 Dasyuridse the same thing 

 takes place under similar circumstances. I am also prepared to find 

 in an herbivorous group like the Phalangistidse 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 (Phascolarctus) in a 

 natural system, I may observe, in the first place, the Wombat 

 (cceteris paribus) shows some affinity to the Phalangistidse in the 

 possession of a thumb, which, th;)ugh short, is very broad and 

 sufficiently distinct. Then, beyond this, we have to add that the 



1 C!f'. Owen, " Classification of the Marsupialia," P. Z. S. 1839, p. 1 9 ; Sclater, 

 Eev. List of Vertebrata, 7tli edition, 1879. 



