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Show 1881.] MR. W. A. FORBES ON THE KOALA. 185 sented, drawn to scale of I the natural size, in the accompanying figures (1 and 2, pp. 186, 187). All four principal lobes are well developed ; but those on the right are far larger than those on the left, the left central being considerably the smallest of these. The umbilical fissure is distinct, extending about halfway across the liver. The right central lobe, which is broad transversely, and forms the largest lobe, is divided very deeply by the large cystic fissure, which extends on the thoracic surface nearly as far back as the umbilical one, and allows the very large and elongated gall-bladder to appear above. Both right and left lateral fissures are also (in this specimen) well developed. The right lateral lobe is large and somewhat oval in shape, but pointed below. The caudate is not present as a free "structure, but it is represented by a somewhat squared, diagonally ridged elevation, lying to the right of the inferior cava, and broadly attached to the substance of the right lateral lobe. The lower border of this elevation is slightly excavated to receive the corresponding kidney. The Spigelian is represented by a smaller thickening, ending in a pointed and free apex, and lying to the left of the vena cava ; it is united over this by hepatic tissue to the caudate. This liver is further remarkable for the great tendency it has to subdivision, numerous fissures, of varying sizes and depths, being developed along the margin of the chief lobes. Their position and relative size will be better understood from the figures than from any verbal description. They are more conspicuous on the visceral than the thoracic surface. The right half of the right central lobe has one such notch on its right external border ; the other half 3, on the right internal border ; the left central has 4, the left lateral 3, whilst the right lateral is still more cut up by about 10. Finally, the caudate has 3 of these supplementary fissures. The gall-bladder is remarkably long, projecting far beyond the anterior margin of the liver, and, as already described, appearing superficially. It is 2 | inches long from its apex to the commencement of its duct opposite the anterior margin of the left central lobe. The free part is connected by a peritoneal investment to the sides of the cystic fissure. In a second liver of Phascolarctos examined (which, however, having been extracted from a spirit-preserved animal, an adult § , is not so well preserved as might be wished) the same general features obtain. The left lateral fissure, however, is less distinct, as is the caudate ; and the left central lobe is smaller proportionally to the left lateral. The Spigelian wants the pointed apex ; and the development of secondary fissures seems to attain an even greater extent1. 1 In Phalangista vulpina the right central lobe is also, as in the Koala, the biggest, and very deeply divided by a cystic fissure. The gall-bladder, however, does not nearly reach the margin of the liver ; the left lateral lobe is much bigger than the right lateral, which is as large as the left central; the caudate is quite free and narrow. All the lobes are remarkably distinct; and their margins are quite simple, with no trace of any such fissures as obtain in the Koala. The liver of Cuscus maculatus is formed on a similar principle, though the right central lobe is not bigger than the left lateral, and the gall-bladder reaches to the liver-margin. All the lobes are simple. The caudate and Spigelian, |
