The dura mater has two layers, or lamellae: The superficial layer (also called the periosteal layer), which serves as the skull's inner periosteum, called the endocranium; and a deep layer called the meningeal layer; the actual dura mater.
The term thagomizer was coined by Gary Larson in humor, in a 1982 Far Side comic strip, in which a group of cavemen in a faux-modern lecture hall are taught by their caveman professor that the spikes on a Stegosaur's tail are so named after the late Thag Simmons.
Just as The Times pulled the plug, though, Larson took a trip to California to interest The San Francisco Chronicle in his work. The Chronicle offered Larson a daily panel, re-named it The Far Side, and began syndicating it to other newspapers.