I love Marc Davis anatomical studies, because they dissect not only the construction of the body but also its motion range. Marc made these illustrations for a planned book, called The Anatomy of Motion. Unfortunately he did not finish the project. There were more drawings to be added as well as text. The main reason why Marc paused was the fact there was no interest in the publishing world for this book, if you can believe such a thing...
He mentioned that he was aiming toward artists and art students, but also physicians. "I wanted to show how things are put together and how they WORK!"
When you combine all that knowledge with a superb sense for design and artistic flair, you are looking at an artist who became invaluable to a place like Disney.
The images are from the 2014 book: Marc Davis, Walt Disney's Renaissance Man
https://www.amazon.com/Marc-Davis-Disneys-Renaissance-Editions/dp/1423184181/ref=pd_ys_sf_s_283155_a2_1_p?ie=UTF8&refRID=1ZH9ZFRS4Y5N2GHK4YZJ
