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The Circulation of the Rhombencephalon

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THE CIRCULATION OF THE RHOMBENCEPHALON The medulla oblongata is supplied with blood by the following branches of the vertebral artery: The posterior and the anterior spinal, the posterior inferior cerebellar and several short bulbar arteries (Fig. 9). The posterior inferior cerebellar (a. cerebelli inferior posterior) winds from before backward around the medulla, runs between the vagus and accessory nerves, enters the vallecula cerebelli and gives branches to the medulla and to the chorioid tela of the fourth ventricle. The anterior spinal artery (a. spinalis anterior) formed by the y-like union of a branch from each vertebral artery, descends along the anterior median fissure; and the posterior spinal artery (a. spinalis posterior) of either side, rising from the vertebral near the lower end of the medulla, descends in front of the posterior lateral sulcus. Both distribute branches along their course. The branches for the most part enter the median raphe or follow the roots of the bulbar nerves, suggesting the centrifugal and centripetal arteries of the spinal cord (Fig. 13). The veins pursue much the same course as the arteries. The anterior median vein joins the ventral veins of the pons and is drained into the cerebellar veins or directly into the superior petrosal sinus. The posterior median vein bifurcates y-like at the middle of the medulla and the two branches wind around the medulla to its anterior surface and empty into the inferior petrosal sinus or the basilar plexus. Issuing from the medulla with the roots of the ninth to the twelfth cerebral nerves are three or four small veins, the radicular veins, which run into the occipital and inferior petrosal sinuses (Cunningham). Both arteries and veins possess perivascular lymph spaces, but there are in the medulla no lymphatic vessels.

The pons Varolii is supplied by the pontal, the superior cerebellar and the posterior cerebral branches of the basilar artery (Fig. 9). The short and transverse branches of the basilar artery, the pontal arteries (aa. pontales). furnish the greater portion of blood to the basilar part of the pons, while the superior cerebellar artery supplies the superior medullary velum and the brachia conjunctiva cerebelli. The branches enter the median raphe, also the substance of the pons elsewhere, especially along the nerve roots, and run at right angles to the surface into it. The deep veins of the pons run forward and form

a plexus on its surface which, according to Cunningham, is drained by a superior efferent into the basilar vein and by an inferior efferent into the cerebellar veins or the superior petrosal sinus. There are no lymphatic vessels in the pons; but, as else where in the central nervous system, there are lymph spaces about the blood-vessels.

The blood supply of the cerebellum is furnished by three pairs of arteries (Fig. 9). The superior cerebellar, from the basilar, supplies all the superior surface except a narrow zone at the posterior border; the anterior inferior cerebellar, also from the basilar, and the posterior inferior cerebellar, from the vertebral, supply the inferior surface and the posterior part of the superior surface.

The Superior Cerebellar Artery (A. cerebelli superior).— Rising from the basilar just behind the posterior cerebral, from which it is separated by the oculomotor nerve, it winds dorsally around the mid-brain to the sulcus lateralis, Nthere it bifurcates into a medial and a lateral branch (Fig. 9). The medial branch continues along the trochlear nerve in the groove between the cerebellum and the mid-brain almost to the median line; and then, bending backward, runs along the superior worm of the cerebellum to its posterior extremity. It distributes branches to the geniculate bodies, corpora quadrigemina, tela chorioidea ventriculi tertii and posterior surface of the pons, besides the vermis superior cerebelli and the medial part of the superior surface of the hemisphere. The lateral branch of the superior cerebellar artery passes from its point of origin near the sulcus lateralis of the mid-brain onto the superior surface of the cere bellum. It runs backward a half-inch from the border of that surface, giving off collaterals along its course. The lateral branch, together with the medial, supplies the superior cerebellar surface almost as far back as the horizontal sulcus of the cere bellum, along which the superior cerebellar artery anastomoses with both the inferior cerebellar arteries.

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