Developmental history of the FT.

<p><b>a</b>) Illustration of two stages of a human embryo by Streeter (1919) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0065974#pone.0065974-Streeter1" target="_blank">[33]</a>, which demonstrates the de-differentiation of the caudal spinal cord into the filum terminale (FT) following the re-absorption of the vestigial tail. The numbers below the drawing indicate the length of the embryo. <b>b</b>) Drawings by Kunitomo (1918) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0065974#pone.0065974-Kunitomo1" target="_blank">[36]</a>of the process of re-absorption of the embryonic tail. The numbers below the illustrations indicate the age in weeks of the fetus, and the numbers above represent the length in millimeters.</p>