In 1568, the anatomist Bartolomeo Eustachi asked the mathematician Federico Commandino to obtain a proportional compass for him. This was an instrument which had been created in the field of geometrical reflection and which was used commonly in cartographical practice at the time. Such a request - and the motivations which lay beneath it - constitute an interesting point of departure from which to look at the circulation of practices and knowledge in the scientific culture of the Early Modern era. In the course of the article, Bartolomeo Eustachi's desire to get hold of the compass is put into relation with his particular conception of anatomy. First, his anatomical method is examined together with the role which images had in it and with the scientific and conceptual instruments which he employed to carry them out. Second, the social and cultural circumstances in which the request for the compass took shape is analysed by means of exploring the profiles of the different players - from patrons to craftsmen -, of their relations among each other and of the places which were the theatre of their interaction.