The functional anatomy of the arachnoid granulations of the upper sagittal sinus was studied by means of micromesoscopic techniques in order to contribute to elucidating aspects of drainage pathways of the cerebrospinal fluid through their fibrous components. The arrangement of fibrous elements was analysed at the base of the peduncle, peduncle, middle and apex of granulation. The analysis of seriate sections shows collagen bundles at the base of the peduncle with a predominantly circular morphology, longitudinally directed towards the peduncle's longest axis. These bundles arise in the middle of the granulation, them branch off towards its apex and periphery. The elastic bundles present an arrangement similar to that described for collagen bundles, delimiting with such bundles intercommunication channels from the base of the peduncle up to the apex of the granulation. Bundles of reticular fibers arranged in between the collagen meshes were found at the base of the peduncle. The fibrous capsule of granulation is ccmposed of collagen bundles and a small number of elastic fibers.