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?