The picture shows a neurosurgical set used for trepanning. The signed instruments are made from polished steel, horn and ebony in a fitted velvet lined embossed leather case.
The craniotomy scalpel (middle bottom) would first be used to divide the scalp.
The hand trephine perforator (top right) would then have been used to start the drilling process and make an indentation to centre the pins for the other drill bits.
The central trepanning brace was for bimanual use whereas the single trephines (left and middle right) were held in one hand. The bits are all parallel (the theoretically safer cone shaped bits popular in the 17th and 18th century had fallen from favour) and the two steel trephines have centre pins which can be removed with a key (to the upper left of the brace).
The brass shafted trephine in the bottom left corner has castellation to accommodate the shavings of bone tissue which would accumulate and it also has an adjustable centre pin. The combination of removable and adjustable centre pins dates the set to circa 1820. The Hey saw (William Hey 1736 – 1819) in the lower middle section has serrations over both the curved and flat surface and this was another method for removing bone in squares formed by the intersection of straight line cuts.
The other methods use for craniotomy referred to above as ‘scraping’ and ‘grooving’ (2) would have been done with simple tools rarely used in Europe and more commonly employed in by the Incas in Peru or Mexico. Similar instruments are in use today in Africa.