The filum terminale
is a delicate filament, about 20 cm. in length, prolonged downward from the apex of the conus medullaris
It consists of two parts, an upper and a lower.
- The upper part, or filum terminale internum, measures about 15 cm. in length and reaches as far as the lower border of the second sacral vertebra. It is contained within the tubular sheath of dura mater, and is surrounded by the nerves forming the cauda equina, from which it can be readily recognized by its bluish-white color.
- The lower part, or filum terminale externum, is closely invested by, and is adherent to, the dura mater; it extends downward from the apex of the tubular sheath and is attached to the back of the first segment of the coccyx.
The filum terminale consists mainly of fibrous tissue, continuous above with that of the pia mater.
Adhering to its outer surface, however, are a few strands of nerve fibers which probably represent rudimentary second and third coccygeal nerves; further, the central canal of the medulla spinalis extends downward into it for 5 or 6 cm.
- - "Vertebral Canal and Spinal Cord: Regions of the Spinal Cord"