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Show 2 2 MR. F. E. BEDDARD ON THE [May 2, to the arteries of the brain, which are most satisfactorily injected in my specimen and which show all the Arctoid characters*. The rhomboidal area formed by the bifurcation of the anterior spinal and its junction with the basilar is of considerable calibre and uniform throughout, as in all Carnivora, which have been examined. The vertebral arteries are, however, peculiar in their mode of joining this rhomboidal vessel. Each vertebral artery in fact divides before joining the rhomboidal, and each branch opens separately into it, as is shown in the accompanying figure (text-fig. 8). The carotids join the circle of Willis just before the middle cerebral arteries are given oft'. Text-fig. 7.- Brain of Helictis personata, dorsal aspect. C'r. Crucial fissure; Lat. Lateral fissure; Orb. Orbital fissure; Pc.S. Precrucial fissure; S.S. Supra-Sylvian fissure. Text-fig. 8.- Brain of Helictis personata, ventral aspect, with the arterial system shown in thicker and thinner black lines. The dotted lines delimit regions of the brain. b.a. Basilar artery ; Ca. Carotids ; Call. Callosal arteries ; P.c. Posterior cerebellar; v.a. Vertebral arteries. Anteriorly the circle of W illis is completed by the fusion of the two callosal arteries, that of the right side being distinctly smaller than that of the left. Text-fig. 7. Text-fig. 8. * Beddard, P. Z. S. 1904, vol. i. p. 183. |