Abstract: The article examines the views of Medieval Italian lexicographers on the structure of the speech apparatus and the principles of its functioning. The author analyses the origins of these ideas, the reasons for the focus on this issue in Medieval dictionaries, and the general and specific features of these ideas. The author considers the ideas concerning the structure of the speech apparatus within the framework of the history of the intellectual culture of Medieval Europe and the scientific (in particular, medical) ideas, which in turn acquired metaphorical parallels in the field of the sign theory of this period. Along with traditional research methods (the principle of historicism and the historical-comparative approach), the author uses special interdisciplinary methods, including above all the linguistic, semiotic, and art criticism methods. The novelty of this research lies in the author’s use of a source new to Russian Medieval Studies, namely, derivational dictionaries. The conclusions made in the article are notable for their novelty and interdisciplinary relevance: in the author’s opinion, the principal interest of Medieval intellectuals, in particular, lexicographers, in the structure of the speech apparatus was due to philosophical and semiotic discussions related to the arrangement of the speech signs and the ability of speech in humans and other living creatures.