A cranial drill, also known as a craniotome, is a tool for drilling simple burr holes (trepanation) or for creating larger openings in the skull. This exposes the brain and allows operations like craniotomy and craniectomy to be done. The drill itself can be manually or electrically driven, and primarily consists of a hand piece and a drill bit which is a sharp tool that has the form similar to Archimedes' screw, this instrument must be inserted into the drill chuck to perform holes and remove materials. The trepanation tool is generally equipped with a clutch which automatically disengages once it touches a softer tissue, thus preventing tears in the dura mater. For larger openings, the craniotome is an instrument that has replaced manually pulled saw wires in craniotomies from the 1980s. History Cranial drill The oldest evidence of a hole being applied on a human's brain with a drill dates from c. 4,000 B.C. The oldest cranial drilling instrument was found in France, and subsequent use evidenced by the Ancient Romans, Egyptians, and in Trepanation in Mesoamerica. The practice of trepanning is also evidenced from Ancient Greece, North and South America, Africa, Polynesia and the Far East. The conceivable reasons why ancient humans developed the technique of drilling the head could be religious, ritual or medical factors. The first trepanning procedure consisted of different types or tools and techniques: at the beginning the only material that was available for use was a sharp and carved rock. The development of The Hippocratic Corpus, written in the fifth century B.C., is the first written source that can be found about trepanning. The aim of the procedure described in "On Wounds in the Head" was to allow the stagnant blood to escape from the head through a hole. The drill that was used at the time is similar to modern ones, but was operated by hand rotation. In the 15th century, people began to believe that drilling was a cure for mental problems due to a magical stone of madness or stone of folly in the head, which had to be removed. Paintings that portray this practice exist, the most significant ones include The Extraction of the Stone of Madness c. 1488-1516 by Hieronymus Bosch and A Surgeon Extracting the Stone of Folly by Pieter Huys. From the Renaissance ages, cranial drilling continued to evolve and surgical practice was used less due