OCR Text |
Show 104 Mil. F. E, HEDDAKD OX THE [Feb. 7, handed over to the Museum of the Royal College of Surgeons, where will also be found some of the other brains described here. The basilar artery and the anterior spinal artery are quite continuous. The junction of the two appears to be marked by the exit of what I presume to be the homologue of the mammalian vertebral arteries. These arteries join the longitudinal vessel on either side in a rather remarkable way. The point of entrance is not lateral, but ventral and median, that of the left side entering posteriorly to the right-hand vessel. These latter, moreover, give off a forwardly-running branch, which diminishes in calibre and effects a second junction with the basilar artery just at the point where the latter receives the right cerebellar artery ; this entrance into the basilar is also ventral and median. The minute details being perhaps individual are not shown in the figure. The anterior spinal artery is double for a considerable distance behind the entry of the vertebral arteries; the two tubes, however, reunite. Both the anterior spinals give off a large number of small trunks to the adjacent regions of the medulla and spinal cord. The cerebellar arteries (text-fig. 15, (7., p. 103) are large and conspicuous ; the right-hand artery arises in front of that of the left side; this asymmetry, it will be noticed, exactly corresponds to that of the vertebral arteries-i. e., the left vertebral artery, like the left cerebellar, is posterior to the right. Each cerebellar artery, before reaching the cerebellum, gives off a strong branch which forms the posterior spinal artery. Of these, at least four run side by side down the posterior face of the spinal cord, contrasting thus with the single or, at least only for a short space, double anterior spinal. The cerebellar arteries pass over the summit of the flocculus and supply all parts of the cerebellum. This region of the brain is, however, also supplied from other sources, which will be dealt with in due course. The basilar artery divides into two just in front of the third nerves ; but the left-hand branch is much the larger, and indeed the right-hand branch might easily escape attention. The carotid arteries (text-fig. 15, Ca., p. 103) lie at the side of the pituitary body, and of course behind the optic nerves ; each artery divides into two branches. The posterior branch runs between the corpus bigeminum and the cerebellum, and receives immediately after its origin the basilar artery. It supplies both corpus bigeminum and cerebellum. The anterior branch curves round the optic chiasma and ends in the ophthalmic artery (text-fig. 15, Opth.) of its own side : there is thus no completed circle of Willis. This main anterior trunk of the carotid has three branches. The first runs between the corpus bigeminum and the cerebral hemisphere, and along the inter-hemispheral sulcus, giving off branches also to the cerebellum. The middle cerebral artery is l ather larger than the posterior. It runs along the depression which has been compared to the Sylvian fissure, giving off branches right and left. It bifurcates, just at the junction of the lower surface of the brain with the upper, into two main branches, of |