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Show 190 MR. W. A. FORBES ON THE KOALA. [Jan. 18, some of the parts, due, no doubt, to age. The clitoris, however, is free at the apex and slightly bilobed l. , '. " i' ,, The brain of the Koala is represented of the natural size in the accompanying figures (figs. 3-6), of which that representing its superior aspect was taken from the brain before being removed from the cranial cavity, and therefore unaltered by displacement or hardening in spirit. The other three figures are drawn from the brain after hardening in alcohol for some months. The cerebral hemispheres are remarkable for their simple surface, which is broken up by no convolutions. Broadest behind, they taper forwardly, and so are somewhat pyriform in outline when viewed from above. They leave the corpora quadrigemina largely exposed behind ; and in consequence the cerebellum is left entirely uncovered : indeed, when the parts are undisturbed (fig. 3) it is not even in contact with the cerebral hemispheres. The greatest length of the cerebral hemispheres is about 1-2 inch ; their greatest depth about 0'7 inch. Viewed from the side, their superior contour is seen to be but little arched behind, whilst anteriorly it slopes downwards away rather suddenly towards the olfactory 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 hemispheres. 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 2 are distinct, the corpus callosum being small and indistinct, and the anterior commissure very large. The hippocampal sulcus is distinct and 1 In Phascolomys wombat, in a two-thirds grown female, I can detect no differences of importance whatever from the type here described. The Fallopian tubes are apparently longer, and their fimbriated extremities better developed. The form of the ovaries, and the disposition of the uteri, vaginae, and urino-genital sinus seem to be nearly precisely similar in the two genera. In Phalangista vulpina. on the other hand, considerable differences occur. The Fallopian tubes are shorter in proportion to the uteri, and are more convoluted. The uteri are more distinct from the Fallopian tubes, are more capacious, and strongly curved outwards. Each os tinea projects as a prominent and quite free papilla into a common vaginal chamber, formed by the coalescence and fusion of the two diverticula present in Phascolomys and Phascolarctos. This chamber is capacious, and has only a very slight indication of a median septum left. In Belideus sciureus the Fallopian tubes and uteri resemble those of Phalangista. The vagina?, however, are much longer and curved on themselves, much as in the Kangaroos. There are apparently two small culs-de-sac; but the specimen examined does not allow me to say whether or no they unite. In Petaurus ( = Belideus?), according to Owen (Anat. Vert. iii. p. 682), where the vagina? are also long and curved, the culs-de-sac remain separate. 2 Vide Flower, Phil. Trans. 1865, p. 647. |