(Chapter 9) Footnote 22:

Lat. discernens; like its synonymns dirimens in the legend for t, u and seiungens in the legend for x, this was changed to communis (with the appropriate syntactic revisions) in the 1555 figure legend, where Vesalius uses the same word consistently for sutures which in separating one bone from another are “common” to the two bones named. In using the same word eight times in eleven lines of text, Vesalius abandons the usual rule of variation in favor of a consistent vox propria.