Filum terminale:

filum terminale.

an extension of the pia mater that extends from the terminal end of the spinal cord to the tailbone. The filum terminale helps to anchor the spinal cord in place.

Learn more: Know your brain - Spinal cord

Watch this 2-Minute Neuroscience video to learn more about the exterior of the spinal cord and this video to learn more about the interior of the spinal cord.