184 ON THE ANATOMY OF THE KOALA. 



lobes. These last are not large, and but little exposed ; in fact, in the 

 undisturbed state, they are covered, when viewed from above, by the 

 hemispheres. The temporal lobe is small. Superiorly the hemispheres, 

 save for a few slight vascular impressions, are altogether smooth ; 

 laterally, a well-defined sulcus, running from the temporal lobe forwards, 

 and curved, first upwards and then downwards, is visible. Anteriorly, 

 this separates off the olfactory tract from the side walls of the hemi- 

 spheres. A slight indentation, about halfway along its course, at the top 

 of its upward convexity, may represent a rudimentary Sylvian fissure. 

 Just behind this is a second similar, though smaller, impression. The 

 olfactory ganglion is large, as is the tract. Internally, the characteristic 

 features of the Marsupial brain * are distinct, the corpus callosum being 

 small and indistinct, and the anterior commissure very large. The 

 P. Z. S. 1381, hippocampal sulcus is distinct and deep, strongly curved, and continued 

 p. 192. forwards over the corpus callosum onto the interna] face of the hemi- 

 spheres 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 hemispheres. The corpus 

 Jlmbriatum and fascia dentata are both distinct. The middle (grey) 

 commissure is very large. Of the corpora quadriyemina, 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 theflocculi, 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 Pliascolomys, 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 flocculi, of the latter. PJialangista has nearly 

 as simple a brain as the Koala ; but iheflocculi 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 twof. "Writing as long ago as 1846, Mr. Gr. E. Waterhouse, in his 

 'Natural History of the Mammalia' (vol. i.), though in that work 

 keeping the Phascolomyidse separate from the Phalangistidae, evidently 



* Vide Flower, Phil. Trans. 1865, p. 647. 



t Cf. Owen, "Classification of the Marsupialia," P. Z. S. 1839, p. 19; Sclater, Key. 

 List of Vertebrate, 7th edition, 1879. 



