Two surgical instruments

The only instruments for opening the cranium considered in this chapter are drills, and in some cases facilitated with a special chisel called a lenticular. There were two kinds of trepan. The modiolus was the Latin name for a crown trepan which had a circular base with teeth which sawed a hole. Then there were the non-penetrating trepans which had a bit shaped to prevent unwanted penetration. They made small openings which could be joined by chisels to remove altogether larger areas of bone than were accessible to modioli. They were the favored instrument from the ancient world up to the Renaissance. At the beginning of the Renaissance, there was a move toward greater use of crown trepans and various methods were applied to stop them sinking too far inward. These included wings in the outer wall and changing the shape of the bit from cylindrical to conic. In time preferences returned to the cylindrical shape and larger diameters. There was also two instruments called lenticulars, the illustrations of which have been confused in the literature. It is now clear that the Roman instrument was shaped to cut the cranium and minimize the need for trepanation. The Renaissance instrument had a different shape and was used to smooth rough bone edges and excise spicules penetrating the meninges. They were simply two different instruments to which the same name was applied.