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Show 144 ON THE POUCH ETC. OF THE MALE THYLACINE. [Feb. 3, quarter of an inch in front of it. On the right hemisphere this fissure is slightly different, as will be seen from a comparison of figs. 2 and 3, and the indentations on the posterior lobe are a little better marked. The second furrow is continuous with the rhinal furrow just in front of the Sylvian fissure ; its course is much the same on both sides of the body. The anterior lobe of the brain cut off by this fissure is U-shaped, a longitudinally running furrow nearly dividing it into two. Sir William Turner* remarks that " the configuration of the brain and the pattern of the convolutions have followed in each order a process of evolution characteristic of the order, the arrangement of the convolutions does not follow the same plan in the various orders. Hence, in the comparison of the brains of mammals with each other, diversities often are recognized which make it impossible to determine the presence of precisely homologous fissures and convolutions in the whole series of the Gyrencephala." It appears to m e that this statement might also be extended in the case of the Marsupials to a single order ; it is extremely difficult to compare the convolutions of the brain of Thylacinus with those of the brain of Macropus. The points which they have in common are :-(1) The strongly marked and continuous rhinal fissure ; but this is found in most mammals. (2) The separation of an anterior lobe (cf fig. 2, p. 141) by a transverse fissure; such a lobe is not for example to be seen in the brain of Dolichotis, nor is it of course to be seen in the " lissencephalous " Koala &c. Judging from Gervais's figures this lobe was particularly conspicuous in the extinct Thylacoleo. M. Gervais's observations upon the cast of the brain of this latter Marsupial are of particular interest in relation to a well-known controversy. I may remark, however, that the brain of Thylacoleo appears to have differed from those of the Wombat and Kangaroo no less than from that of the Thylacine by the outward direction of the longitudinal furrow dividing the anterior lobe. However, in Halmaturus bennetti the furrows in question are intermediate between the two extremes, being straight. It appears to me that Halmaturus and Hypsiprymnus come much nearer to Thylacoleo than the Wombat does in the form of their cerebral convolutions. M . Gervais himself considers that the Wombat is the closest ally of Thylacoleo in these points of structure. (3) In common with many other lower mammals, the lobus hippocampi is not marked by furrows, and is not covered by an extension downwards of the pallium. Finally, of course, there are the important differences in the commissures. With the exception of the Sylvian fissure and the sulcus which divides off the anterior lobe of the brain and the rhinal furrow, it seems to me to be very difficult to compare the furrows and convolutions of Thylacinus with those of the Diprotodont Marsupials. The Sylvian fissure is directed at first slightly forwards, and then 1 Loc. cit. p. 152. |
