Anatomically Correct Multi-Faced Demons

Question

Demons in medieval art were often depicted with many extra faces over their body. Specifically:

• The shoulders, knees, and elbows may be replaced with complete mammalian heads, with eyes, nose, and a mouth through which the rest of the limb grows
• The pelvis may be replaced with a downcast mammalian skull, with eyes, nose, and a mouth from which both legs grow
• The chest and belly may have a face, with eyes, nose, mouth, and skeletal structure, growing at the front
• The genitals may be replaced with a forward-facing humanoid head/face, with eyes, nose, and mouth

All of these parts should work as well as the original (i.e. head-joints are as strong and have a similar range of motion), and each facial replacement is more-or-less independent from the others, and can combine in any permutation

What sort of anatomy could these extra heads have to allow such structures to exist?

Answer 1

There are no modern criteria for demons

I find it doubtful whether a demon could be labeled "Anatomically Correct", because there exists no reference of "correct" for any biological purpose. We don't know enough. Has a demon spawned from an animal, e.g. a bat, or a goat, at some point in evolution ? Would a demon require food ? How do demons move ?

Topics like "anatomy" were no issue in medieval art. If you look at medieval bestiaries, picture books describing animals, there were loads of beasts from mythology that got mixed in, creatures with multiple heads, both hooves and claws, depending on the nature of the demon and the intent (story) of the artist depicting it.

Demons are symbolic entities of evil, they served to show evil in medieval times. They exist in the depictions and these depictions don't require a modern biological description, they serve culture and religion.

The painted demon does not require a viable shape, it just has to look bad. Two faces comes out handy, but designing a proper (or "correct") anatomy would require witchcraft,

Some demon shapes are more plausible.. but still, with modern scientific insights, biologists would never designate an ape-like creature with goat horns, bat wings and 6 limbs as anatomically correct.. For instance, below demons could have evolved on some planet.. suppose a goat-like creature would develop flight, then stop flying and (for some reason) develop horns, ape-like limbs and bipedalism, you get these,

As for the multi-facial aspect of this question, I cannot resist to put below one, a quite modern demon, whose head may at least be "creature-designable" ! This one has three faces and one brain,

The artist is acidpicasso on Deviant Art

Answer 2

Here is a frame challenge.

What is a demon?

If a demon is a devil, which is a common usage of the word "demon", then a demon/devil cannot be anatomically correct. A devil is not supposed to be a living being.

In Christian theology, a devil is a spirit. It is an angel - a fallen, evil angel. An angel doesn't have or need a body. But an angel that comes to the physical world can take particals of matter from the physical world and arrange them to make an imitation of a bological body, and make that body move as though it was alive. So angels can more or less make robot bodies for themselves, bodies which can look like nonliving forms or like life forms, or like glowing balls of light, or like whatever they want.

And the same goes for devils. In fact grimiores - spell books - claim that specific important devils take on specific forms for dealings with witches and sorcerors, so that each one might look like an alien from a different planet and belonging to a different species than any other. And I'm not talking about aliens who look as human as Vulcans do either. Not at all!

If a demon is not considered to be the equivalent of a Christian devil, but more like a daemon or an ancient Greek diamon, I am not so certain that it will be totally a spiritual being. But I rather doubt it would be any sort of biological being.

I suspect that any type of demon could change the shape of its nonliving body as easy as a human can change clothing.

If, like E.R. Eddison, you plan to write a fantasy story where there are beings called demons who have living biological bodies which are set in one specific form and cannot be changed, and in short are biological animals like humans or aliens from other space, then your will have the problem of designing anatomically correct forms for your so-called "demons", which will be be real demons just about as much as you and I are. If you want your so-called "demons" to have multiple faces you will have to try to make having multiple faces plausible for living biological beings.

And perhaps you might want to find out if any animals or humans have ever survived with multiple full or partial faces and/or heads. I personally would find such research rather creepy.