I have bought animal skulls on eBay, i.e. beaver, for my
classes. I also bought 2 pidgeon, 1 frog and one snake.
These skulls and skeletons make excellent drawing
references. I noticed years ago that at portfolio reviews
at colleges, the recruiters were most impressed with the
'bone' drawings. I push composition and values, using a
viewfinder and the results are always impressive.