Franciscus dele Boë, or Sylvius, was born into a family of French Huguenots who had moved to the province of Hessen. He studied medicine in Sedan, Leiden and Basle. He was a private teacher in anatomy in Leiden for some years, and while teaching he drew the attention of his students to the long fissure on either side of the cerebral surface. He practised successfully as a physician in Amsterdam from 1641 onwards, until he was recalled to the chair of medicine in Leiden in 1658. He emphasized the role of chemical processes in the human body (iatrochemistry).

Conflict of interest: none declared. Financial support: both authors work part time for the Association of the Dutch Journal of Medicine (Vereniging Nederlands Tijdschrift voor Geneeskunde), Amsterdam.