Filum terminale

The filum terminale ("terminal thread") is a delicate strand of fibrous tissue, about 20 cm in length, proceeding downward from the apex of the conus medullaris. It is one of the modifications of pia mater. It gives longitudinal support to the spinal cord and consists of two parts:

  • The upper part, or filum terminale internum, is about 15 cm long and reaches as far as the lower border of the second sacral vertebra. It is continuous above with the pia mater and contained within a tubular sheath of the dura mater. In addition, it is surrounded by the nerves forming the cauda equina, from which it can be easily recognized by its bluish-white color.
  • The lower part, or filum terminale externum, closely adheres 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 in a structure sometimes referred to as the coccygeal ligament.
Filum terminale
Cauda equina and filum terminale seen from behind. The dura mater has been opened and spread out, and the arachnoid has been removed. (Filum terminale labeled at center right.)
Sagittal section of vertebral canal to show the lower end of the medulla spinalis and the filum terminale.
Li, Lv. First and fifth lumbar vertebra.
SII Second sacral vertebra.
1. Dura mater.
2. Lower part of subarachnoid cavity.
3. Lower extremity of medulla spinalis.
4. Filum terminale internum.
5. Filum terminale externum.
6. Attachment of filum terminale to first segment of coccyx.
Identifiers
TA98A14.1.01.401
TA25384, 5414
FMA83977
Anatomical terminology

The most inferior of the spinal nerves, the coccygeal nerve leaves the spinal cord at the level of the conus medullaris via respective vertebrae through their intervertebral foramina, superior to the filum terminale. However, adhering to the outer surface of the filum terminale are a few strands of nerve fibres which probably represent rudimentary second and third coccygeal nerves.[1] Furthermore, the central canal of the spinal cord extends 5 to 6 cm beyond the conus medullaris, downward into the filum terminale.

Additional Images
  • Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view.
  • Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view.
  • Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view.
  • Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view.
  • Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view.
  • Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view.
  • Spinal cord. Spinal membranes and nerve roots.Deep dissection. Posterior view.

References
  1. Susan Standring (7 August 2015). Gray's Anatomy E-Book: The Anatomical Basis of Clinical Practice. Elsevier Health Sciences. p. 762. ISBN 978-0-7020-6851-5.

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

  • Martini, F. Timmons, M. and Tallitsch, R. Human Anatomy. 5th ed. San Francisco: Pearson/Benjamin Cummings, 2006.
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