![Woodcut showing corpse draped over a table with half of its head removed to expose brain](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg7miRogaAKRnkQREKlJXzDiwCWNobiOQdGCSrnnoE4KZBAQ3AdiNCcKrveJ_l2FjWcKQs46gp3syYm0aV8hTcMEsyoBYJD3LFi5n7_5x8NvSXxzUW4abCwef5meViuo2KO2UhhNPjUudk/s320/DSCN0632.jpg)
If you look a little closer, you'll notice an odd square around the top of the head. The effect is more pronounced in other illustrations in the book. You can really see it here:
It turns out that Estienne was dissatisfied with the woodblocks for the book, and had portions of them recut to emphasize crucial anatomical detail. The result is a woodcut inside of a woodcut. He clearly saw the original as a failure of execution--on the part of the woodcut artist.
We are lucky enough to have first editions of both of Estienne and Vesalius. To see them ask for Rare QM21.E82 and Rare QM25.V4.