Vintage Russian model life-size human skull teaching aid.
This is certainly an unusual item. It is an old Russian medical training model that came from a collection of Russian items that appear to have come from a biology class / laboratory.
It is made from plaster, probably overlaying wire mesh or something underneath to give it structure and strength. The plaster has then had a coat of paint to give it a bone colour. On top of this there are various annotations to point out specific features and an old label which was probably the item number in the collection.
Over the years, the mandible has become separated although the springs to articulate it are still present. As you can see in the photos, some of the plaster has also been damaged over time. Not surprising if it was a teaching aid and heavy-handed students.