This is an impressive undertaking, but good lord, what an unfortunate name.
There are sphincters in your eyes.
There is a sphincter in your esophagus.
Your body is full of sphincters.
The anal sphincter is just one of many sphincters.
And now you really do know.
As an example, if people lived on Venus, they would be called "Venerials" by the proper genitive form. Alas, doctors got to it first (Venus, Roman goddess of love...) so it was changed to "Venutians". (Source: Neil DeGrasse Tyson's podcast, StarTalk radio).
Still true though.
I'm going to keep telling myself that your use of 'genitive' right next to 'Venerials' was entirely conscious and deliberate.
I'm sorry, but this cracked me up. It brought out my inner Beavis and Butthead. I apologize. But, I mean, come on. Most people do associate the word sphincter with the butthole, and surely the creator should have known that. (Unless the, umm, cheeky association is intentional?)