I'm amazed at how little printed information exists about the anatomy of wild animals and how hard it is to find it. Any university bookstore has books with anatomy schemes of cows, dogs and other domesticated animals, but schemes of muscles or bones of any wild species are rare, often only found scattered in specialized reviews. Over the years I've collected on internet several gigabytes of anatomy schemes, skeleton photos, dissection photos etc., and I've bought the best books I could find on the topics. I've found stuff about some really exotic species but not as much as I'd like to. In order to find information on penguin fin muscles I had to dig them out of the Challenger Reports, the logs of an XIX century explorer ship, which also contain a few thylacine dissection drawings - very few of them, possibly the only existing study of this kind, of a species which nobody will be able to study again...
The rest of the Challenger drawings is here (links to chapters are towards the bottom of the pages).
Puffins are regularly eaten in some countries but good luck finding a scheme of their wing muscles. I could only find very crude schemes from a cute study about their swimming motion. I see it's not very useful information for most people, but it's kinda... embarassing? To discover we are so abysmally ignorant about many animals we like a lot, like penguins. We kill them by the milions and treat most of the corpses as trash, yet it seems nobody bothers to take a closer look at the little wonders.