The filum terminale ("terminal thread") is a delicate strand of fibrous tissue, about 20 cm in length, extending inferiorly from the apex of the conus medullaris to attach onto the coccyx.

[3] The upper portion of the filum terminale is formed by spinal pia mater within a dilated dural sac, while the lower portion is formed by both pia and dura mater (with the outer dural layer closely adhering to the inner pial component).

[3] It is contained within a tubular sheath of the dura mater and is surrounded by the nerves of the cauda equina (from which it can be easily recognized by its blueish-white color).

[5] The central canal of the spinal cord extends inferiorly into the superior part of the filum terminale.

[3] This article incorporates text in the public domain from page 750 of the 20th edition of Gray's Anatomy (1918)