The original "labyrinth" was the home of the fierce monster
of Greek mythology, the Minotaur. It was a cave with endless tortuous
pathways. Anyone who was foolish enough to venture into it would be lost forever, or
until eaten by the Minotaur, whichever came first...usually the latter.
From this comes the English word "labyrinthine," meaning endlessly convoluted
and complex (like my prose!). The use of the term in anatomic sense means
any coiled and convoluted structure.
The mosaic at left shows the slaying of the Minotaur by Theseus. Theseus was vary clever: he knew he'd have to find his way out of the labyrinth, so as he went deeper in search of the monster he unspooled a thread behind him, and after the deed was accomplished, he simply wound it up and followed it home.