. Cunningham's Text-book of anatomy. Anatomy. INTEKNAL STEUCTUEE OF MEDULLA OBLONGATA AXD PONS. 553 exPAvs plexuses, which are situated at the three corners of the epithelial roof of the ventricle, oval or elliptical perforations develop in the roof at about the fifth month of foetal life. These are known as the apertura medialis ventriculi quarti ( foramen of Magendie). which opens between the clavse on the posterior sur- face and the aperturae laterales upon the anterior (Eig. 527), behind the insertion of the glossopharyngeal nerve on each side. Through each of these lateral openings th
. Cunningham's Text-book of anatomy. Anatomy. INTEKNAL STEUCTUEE OF MEDULLA OBLONGATA AXD PONS. 553 exPAvs plexuses, which are situated at the three corners of the epithelial roof of the ventricle, oval or elliptical perforations develop in the roof at about the fifth month of foetal life. These are known as the apertura medialis ventriculi quarti ( foramen of Magendie). which opens between the clavse on the posterior sur- face and the aperturae laterales upon the anterior (Eig. 527), behind the insertion of the glossopharyngeal nerve on each side. Through each of these lateral openings the great swollen cauliflower-like extremity of the chorioid plexus becomes extruded from the ventricle. The inferior extremities of the two plexuses lying side by side present an analogous relationship to the apertura medialis, but they are exceed- ingly attenuated and the epithelial lamella from which they spring becomes dragged backwards into contact with the cerebel- lum (Fig. 477), so that, when seen from below, the apertura medialis is a great funnel-shaped tube leading into the fourth ventricle and the chorioid plexuses look like two delicate vascular fringes on the cerebellum. These three apertures are the only means provided for the escape of the fluid contained in the ventricles of the central- nervous system. The fluid is poured into a space, enclosed by the arachnoid, which is called the subarachnoid space. As a result of the pontine flexure the lateral walls of the neural tube in the neighbourhood of the bend fall away the one from the other and eventually come to be placed in the same transverse plane,. Fig. / 483, — Transverse Sections across the Medulla Oblongata is two Human Embryos, representing Different Stages in the Ex- pansion of the Roof and the falling later- ally of the Lateral W7alls. (From His, slightly modified.) Cerebrum .Mesencephalon ^Early cerebellum one with the other and also with the floor-plate. At the time this process is in operat
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1914
