The futakuchi-onna is a creature with a unique anatomy. They outwardly appear human, with one critical difference: in addition to the normal human mouth, they have a second, slightly more monstrous mouth in the back of their heads with a pair of long, serpentine palps beside it. The mouth has lips, teeth, and a tongue, and is capable of eating food and functioning normally. The mouth opens vertically like a tetrapod and is just small enough to be hidden under the hair, with the palps being around a meter long.

What is the most plausible internal head anatomy, with regards to the joints and how things link together?

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    $\begingroup$ What is a tetrapodal-looking mouth? $\endgroup$
    – L.Dutch
    Sep 26, 2021 at 14:48
  • $\begingroup$ @L.Dutch A mouth that resembles that of a basic tetrapod, with teeth, lips, tongue, etc $\endgroup$ Sep 26, 2021 at 14:53
  • $\begingroup$ @L.Dutch you know how some people just put one foot in their mouth? Well... $\endgroup$ Sep 26, 2021 at 18:06
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    $\begingroup$ (also, for the downvoters: I can understand why you might not like this kind of question, but downvoting without commenting as to why, or how things might be improved, is unlikely to improve matters) $\endgroup$ Sep 26, 2021 at 18:08
  • $\begingroup$ If you feel like my edit isn't satisfactory feel free to just remove it. I just feel like it's better to just describe the mouth, since tetrapod mouth can mean a number of different things (are the teeth specialized like In mammals or non-specialized like in reptiels and fish? Are they like those of a carnivore, omnivore or herbivore? Is the mouth just like that of a human but with sharp teeth instead, like in some of the many depictions of this yokai?). $\endgroup$ Sep 26, 2021 at 19:00

1 Answer 1


Basically a Mirrormaid

The strategy to considering the form and function of a futakuchi onna is to mirror the ventral oral anatomy onto the posterior aspect of the cranium.

You'll need the same buccal, maxillary & mandibular structures: bones and muscles and nerves of the lower face. You'll need the same oro-pharyngeal structures: tonsils, tongue, and gullet.

You won't need the upper face or the larynx. Just an esophagus. The esophagus could either be pierced by the spine and thus temporarily split into two before entering the thoracic cavity and merging with the main esophagus. Or alternatively, one of the branches might atrophy and be resorbed during the fetal stage.

Most images of such people don't take anatomy into account:

enter image description here

This image of a futakuchi onna basically shows a mouth stuck right onto the occiput. Even though the posterior mouth is shown to be eating, not enough room is given for all the functional bits.

This image of Quirrell~Riddle is beautifully made, but demonstrates the same problem.

enter image description here

Give me a bit and I'll compose an image.


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