Three Heads, One Hat

A three-faced figure is depicted to look like a jester’s bauble, complete with a jester hat and collar, this latter ending in quill’s nibs suspended over an ink bottle.
This illustration, which appears on the title page of the book, was known by all contributors as “Three heads under a single hat.” It represents the authors of the written pieces.

The caption reads in the original French: Trois têtes sous un même bonnet.