What ancient practice involved using a circular instrument to cut sections of the skull?

The practice referred to is trephining, which is an ancient surgical technique in which a circular instrument is used to remove a section of the skull. This method dates back to prehistoric times and was often performed with the belief that it could treat various conditions such as head injuries, mental illness, or to release evil spirits believed to cause ailments. The act of creating an opening in the skull was thought to relieve pressure or allow for the expulsion of harmful entities.

In this context, trephining specifically denotes the practice that involved cutting out a piece of the skull, which is critical to distinguishing it from related terms. While trepanation is often used synonymously with trephining, it is important to recognize that the choice of "trephining" closely aligns with the traditional terminology associated with this ancient medical procedure.