[jac241]

That is known as the perforator drill bit - https://www.reddit.com/r/toolgifs/comments/z2zikm/cranial_pe...

Used to make burr holes so that the dura can be stripped away from the skull using the Penfield 3 instrument.

Then what's used is what's known as the B1 with footplate to create the bone flap - https://www.researchgate.net/publication/323134344_Exposure_...

Here is an example of the drill system - Midas Rex MR8 - https://www.ebay.com/itm/125960633809

Here's a video of a surgeon performing the pterional craniotomy, probably the most common craniotomy for things like aneurysms, - https://www.neurosurgicalatlas.com/volumes/cranial-approache...