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.
About Gary Larson. The Far Side was syndicated in more than 1,900 daily newspapers from 1980 to 1995, when Gary Larson retired. During its run, the cartoon spawned 22 books from AMP, which were translated into a total of 17 different languages.