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Show 1904.] OF THE BRAINS OF MAMMALS. 195 the human arterial arrangement appear to be the long distance from tlxe middle cerebx-al artery of the anterior communicating artery, and tlxe fact that the two callosals fuse together immediately after their origin from the anterior cerebrals. Suricata tetradactyla and Arctictis have a cerebral arterial system which is constructed upon the same plan. It will be remembered * that the cerebral arterial system of M a n differs from that of, at any rate, some Apes and Lemurs in the fact that there is an anterior communicating artery and that, apart from this connection, the two callosal arteries remain separate. In tlxe Apes and Lemurs, on the other hand, the two callosal arteries are given off early and immediately fuse to form a single callosal artery which, later, divides. This condition seems to m e to be simply an exaggeration of the anterior communicating artery. N o w precisely the same thing occurs among Text-fig. 22. 0. 0. Anterior cerebral system of (A) Myopotamus coypu, (B) Lagostomu s trichodactyJus, (C) Tamandua tetradactyla. For d and/see text, p. 196. Other letters as in text-fig. 21. the Carnivora. Ixx the genera Ursus, Ictonyx, Galictis, and Mitstela the disposition of the callosal arteries is as in the Apes ; while, as already mentioned, certain ^Eluroid genera agree with Man. The classificatoxy significance of this cannot be passed over; and I would specially direct attention to tlxe fact that the * See for example Beddard, supra, p. 161. 13* |
