Hieroglyphics of Horapollo, tr. Alexander Turner Cory, , at sacred-texts.com
When they would denote an amulet, they pourtray TWO
[paragraph continues] HUMAN HEADS, one of a male looking inwards, the other of a female looking outwards, (for they say that no demon will interfere with any person thus guarded); for without inscriptions they protect themselves with the two heads.
46:1 Mr. Birch has suggested, that φυλακτήριον has been substituted by Horapollo for φύλακα, a Guard or Protector; which is extremely happy.