A glaciated planet where the Eymorg women live underground and the Morg men survive on the frozen surface, the destination of Spock's stolen brain.
Sigma Draconis VI is one of several inhabited planets in the Sigma Draconis system. Its surface is locked in an ice age and is home to the Morgs, primitive men, while the Eymorgs, the women, live in an advanced underground complex left by an earlier civilization.
In Spock's Brain, the Enterprise traces the ion trail of Kara's ship to this world and finds that Spock's brain is running the Controller. Kirk's party recovers it, and with the Controller gone, the two halves of the planet's population must learn to live together on the surface.