Illustration study

[Fishbaum]

I'm new to all things Voynich, so forgive a naive question.

In all the papers I've seen on the Voynich manuscript, the investigations are all about the text. Has there been an extensive study of the style of the illustrations? It strikes me that the somewhat crude, cartoonish style might be correlated to the late 19th century, perhaps even to a self-taught artist. Any definitive studies on the style, placing it within the 15th century?