Relationship of the Tela Choroidea and Inferior Medullary Velum to the Fourth Ventricle. B, The cerebellar tonsils have been gently retracted to expose the uvula, which is located behind and hides the nodule of the vermis. The uvula hangs downward between the cerebellar tonsils, thus mimicking the situation in the oropharynx. The tela choroidea, in which the choroid plexus arises, encloses the lower portion of the roof of the fourth ventricle and has an opening, the foramen of Magendie, located at the caudal end of the fourth ventricle. C, Enlarged view. Both cerebellar tonsils have been removed to expose the inferior medullary velum and the tela choroidea, which form the lower half of the roof of the fourth ventricle. The velum arises on the surface of the nodule, which is located deep with respect to the uvula. The telovelar junction is the line of attachment connecting the tela choroidea to the inferior medullary velum. The taeniae are small ridges along the lateral edge of the floor of the fourth ventricle to which the tela choroidea is attached. The tela choroidea forms the lower wall of the lateral recess. The inferior medullary velum, at the level of the lateral recess, narrows to a small band, the peduncle of the flocculus, to which the flocculus attaches. The choroid plexus attaches to the inner surface of the tela choroidea and protrudes through the foramen of Magendie in the midline and through the foramina of Luschka into the CPAs behind the glossopharyngeal and vagus nerves. D, The tela choroidea in the right half of the roof has been removed to expose the interior of the fourth ventricle. The inferior cerebellar peduncle forms the upper and anterior walls of the lateral recess. E, Removal of the tela choroidea on both sides exposes the whole lower half and almost all of the upper half of the fourth ventricle. Removal of the lateral portion of the tela choroidea exposes the anterior and upper walls of the lateral recess, both of which are formed by the inferior cerebellar peduncle. The inferior medullary velum, which is paper thin, has been preserved. The superolateral recess (dashed line) is located immediately above the lateral portion of the inferior medullary velum. (Images courtesy of AL Rhoton, Jr.)