A Summer spent visiting museums has left me a little hooked on historical natural illustration (amongst many, many other things).
The American Museum of Natural History are posting images from their archives on a few pinterest boards, the Vertebrate Zoology Anatomy Illustrations board is probably the pick of the bunch.
It looks like they rotate the images they have up on the board periodically. The Natural Histories board also has a few nice pics.
Also worth mentioning, you can pick up Art of Nature by the Natural History Museum (London) for £4 here. The illustrations are grouped by continent and it’s a good mix of people, plants and animals (certainly worth £4!).
Currently in my Amazon basket I’ve also got Curious Beasts, a collection of animal illustrations from the 15th-19th centuries produced by the British Museum. I missed the exhibition when it came to the Midlands though I was lucky enough to catch a similarly themed exhibition in Copenhagen a few years ago (complete with mermaid skeleton), I imagine I’ll know a few of the prints already but even if not I’m fairly sure it’ll be up my street.