In this work Stensen, in collaboration with the mathematician Vincenzio Viviani (1622-1703), a pupil of Galileo, developed a geometrical description of muscular contraction, and attempted to show theoretically that muscles did not increase in volume during contraction. The appendix contains his anatomical descriptions of the head of two sharks. In discussing the relationship of the shark teeth to similar-shaped fossil stones found in the Mediterranean, Stensen developed theories of how geological structures and fossils might be formed. This was translated by A. Garboe as The earliest geological treatise (1667), London, 1958.