Why is the Frankenstein's head squared-off?

[Ranchoth]

(Referring to the monster, of course, and the 1931-onward Universal Studios version, specifically)

Ever since I was a kid, I’ve been familiar with the explanation by Frankenstein makeup artist Jack Pierce:

“I did three months of research in anatomy, surgery, criminology, ancient and modern burial customs, and electrodynamics. My anatomical studies taught me that there are six ways a surgeon can cut the skull in order to take out or put in a brain. I figured that Frankenstein, who was a scientist but no practising surgeon, would take the simplest surgical way. He would cut the top of the skull off straight across like a pot lid, hinge it, pop the brain in, and then clamp it on tight. That’s the reason I decided to make the Monster’s head square and flat like a shoe box and dig that big scar across his forehead with the metal clamps holding it together.”

The thing is, I’ve never understood how that translates to a monster with a square skull, rather than just like, say, the monster from Young Frankenstein, with a dome-ish cranium. Am I missing something in the proper visualization of the skull-hinges, or is there some additional information that Pierce was glossing over?

Can anyone help me out with this question of such prime importance?

(And yes, I probably should have saved this for Halloween. Ah, well.)