Even though I paint quite a bit of highly rendered bones/skulls—I often do timed sketches and studies to improve on selective abstraction (adding weight to aspects of constancy.) Glad to see you are doing this Bert!
There are many great resources online for reference as well if you are doing anatomy studies. I added this one a little while ago:
http://www.smartermarx.com/t/resource-zygote-body-online-anatomy-program/212