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 University of Cambridge in the UK. Found in a dusty part of the University's collection, analysis of the cut reveals that it was done with reasonable precision. Unlike some of the samples that Dittmar has studied -- such as samples 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]
Picture: Jenna Dittmar