>>3736919>>3736929It's a reference book endorsed by several artists I follow on Twitter, all of them Japanese.
Hi_ton_ton is one of them
It more or less describes the animal's anatomy, and suggest how it would inner skull or muscle would be like for beast men.
I certainly isn't a shortcut to how to draw better, but I think it's a good book due to how it makes designing beastmen character easier as it helps you understand how their anatomy works