Caudal aperture of the central canal at the filum terminale in primates.

An aperture has been observed in the central canal at the filum terminale in some lower vertebrates and some mammals but not in the human. We examined 8 human spinal cords and 2 macaque monkey spinal cords and detected a caudal aperture in both human and monkey filum terminale. The ependymal lining of the human terminal ventricle was found to begin direct contact dorsally with the pia mater at 12.8 +/- 5.3 mm caudal from the most cranial root of the 5th sacral nerve (S5). In the human spinal cords the central canal was found to open into pia-arachnoid space at about 16.5 +/- 5.0 mm caudal from S5. Typical size of the caudal aperture was about 150 microns long x 130 microns wide. In the monkey filum terminale the caudal aperture appeared at about 45 mm caudal from S5. The opening was about 100 microns long x 65 microns wide. The cytoplasmic process of the pial fibroblast was contiguous to the ependymal cell at the site of opening.