In the time of dinosaurs: When Ms. Frizzle takes her class to a dinosaur dig to look for Maiasaura nests, the Magic School Bus turns into a time machine and transports them back into prehistoric times--when dinosaurs roamed the Earth. Inside the human body: When the school bus, Ms. Frizzle, and the entire class magically shrink and accidentally enter Arnold's mouth, the ensuing anatomical adventure proves educational as well as exciting.