Is it permissible to bring a skull into the house for medical study, and does that prevent the angels from entering?

In summary, bringing a skull into the house for the purpose of study, if it is from an animal that was ritually slaughtered, is permissible without dispute. If it is from an animal that was not ritually slaughtered, there is a difference of opinion among scholars regarding the utilization of bones from a carcass, but the preponderant view is that it is permissible for the purpose of learning. However, if the skull is human, it is not permissible to keep it, as it violates the sanctity of the human being, even though some contemporary scholars have permitted human dissection for the purpose of medical study. If the skull is made of plastic materials, there is no harm in keeping it, as it is not a complete, full-bodied image, and thus does not prevent angels from entering the house.