As we have discussed in the previous post, Tom Buijtendorp e Maja d'Hollosy used also a coin for their awful rendering of the head of Julius Caesar, besides the busts of Leiden and Tusculum. In their rendering, the head had been deformed to become very large on a very thin neck. The eyes are small, to increase the deformity.
Now, the coin used is a Denarius with head of Julius Caesar, struck under M. Mettius, Roman Republican Period, 44 B.C. Here in the image the coin.