Tela Choroidea and Inferior Medullary Velum of Fourth Ventricle. The right cerebellar tonsil has been retracted to permit visualization of the inferior aspect of the fourth ventricle. The tela choroidea is a thin membrane that lies between the cerebellum and the lower part of the roof of the fourth ventricle.  It is formed of two tightly adherent histologic layers: a surface covering of pia mater, and a deeper, underlying layer of ependyma of the fourth ventricle. During a telovelar approach to the fourth ventricle, it is necessary to dissect through the tela choroidea to permit visualization of the fourth ventricular floor. (Image courtesy of AL Rhoton, Jr.)