This represents the background to an instrument that was clearly never meant to be assembled in the book. 

This image appears on sig. B3r of Apian's Instrument Buch.  The various parts one would attach to this background in order to construct the instrument it represents are printed on sigs. B3v and B4r, following.  The images are integrated with the text in such a way as to make it clear, even to those of us who don't read c16th German, that they were never meant to be cut out and assembled elsewhere in the book.

Image used Courtesy of Smithsonian Institution Libraries