I have finished the full skeleton. It took me a few months here and there using a few reference sources. For the main shapes and understanding of orthographic views, I bought Paul Richer Artistic Anatomy which I recommend for the images and information in the book. For a more in depth anatomy understanding, I took KenHub susbcription online. It is a great tool to have for any artist who needs information on anatomy. Last, I used Anatomy Standard for the 3D references and details. I greatly recommend that you check out their website for references on bones.