Don't worry: that vertical cut was made after the subject died. In fact, it's an incredibly rare example of vertical skull dissection, most likely performed at the end of the 1800s as a teaching aid.
The skull was discovered by Jenna Dittmar from the Cambridge University. Found in a dusty part of the uni's collection, analysis of the cut reveals that it was done with reasonable precision.
This was quite unlike some of the other samples that Dittmar has studied, apparently – such as those from the 1700s, where she noticed medical practitioners had "sawed off the top of a skull horizontally, like a boiled egg", reports New Scientist. Nice. [New Scientist]
Image by Jenna Dittmar