OCR Text |
Show 1905.] ARTERIES OF THE BRAIN IN BIRL'S. 115 text-fig. 20) in which the encephalic arterial system of this bird difiers from that of other birds. The anterior spinal is double for a considerable distance behind the origin of the cerebellar arteries ; but I am unable to be precise as to the extent of this double region. The anterior spinal artery is not exactly in the same straight line with the basilar artery, but joins directly the left cerebellar artery. There is thus, as is so often the case, an asymmetry in the cerebellar arteries; but the most remarkable peculiarity concerning these arteries is that they rise very near to the circle of Willis, and therefore well in front of the origin of the sixth pair of nerves. Text-fig. 20. Lettering as in text-fig. 15. The basilar artery joins the right side of the circle of V' illis only. The latter is more elongated in an antero-posterior direction than it is in many birds. The posterior cerebral artery among birds usually hides itself |