The Doyen instrument and its use
I’ve posted similar tools used for making trephine holes in the skull (in modern medicine, used for relieving cranial pressure in emergency situations), but none of the illustrations have demonstrated the use of the tool.
On the right, you can see the Doyen instrument being used on the bony vault of the skull, with the brain underneath.
Diagnosis and Treatment of Brain Injuries, With and Without a Fracture of the Skull. William Sharpe, 1920.