The Tenth Galaxy was the largest of the Outer Galaxies, represented by Trantis on the Galactic Council. (TV: The Daleks' Master Plan)

The Fourth Doctor read The Origin of the Tenth Galaxy, a book written by a Time Lord historian. One item featured in the book was Magla, a life form mistaken for a planet. (PROSE: Doctor Who and the Destiny of the Daleks)

It is uncertain if the Tenth Galaxy is part of the Ten Galaxies
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