One of the many kinds of monster found in the margins of illuminated MSS or in cathedrals. Blemmyae were creatures somewhat like human beings, except they lacked heads: their eyes and mouths were on the chest. The name is taken from a people of Nubia, known to the Romans in the 3c and later. Fable and ignorance transformed them into acephalous creatures.
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.