Sources : Amphisbaena

Lucan [1st century CE] (Pharsalia, book 9, verse 800): Dread Amphisbaena with his double head / Tapering... - [Ridley, 1919 translation]

Pliny the Elder [1st century CE] (Natural History, Book 8, 35; 30, 25): [Book 8,35] ...that the amphisbaena has a twin head, that is one at the tail-end as well, as though it were not enough for poison to be poured out of one mouth... [Book 30, 25] For feverish chills Xicander gives as a remedy a dead serpent, the amphisbaena, worn as an amulet, or even its skin; nay, he says that, if it is fastened to a tree that is being felled, the fellers feel no cold and do their business more easily. So much does this, alone of serpents, stand up to the cold, being the first of all serpents to make its appearance, even before the cry of the cuckoo. - [Rackham translation]

Aelianus [170-230 CE] (On the Characteristics of Animals, Book 9, chapter 23): The Amphisbaena however is a snake with two heads, one at the top and one in the direction of the tail. When it advances, as need for a forward movement impels it, it leaves one end behind to serve as tail, while the other it uses as a head. Then again if it wants to move backwards, it uses the two heads in exactly the opposite manner from what it did before. - [Scholfield translation]

Gaius Julius Solinus [3rd century CE] (De mirabilibus mundi / Polyhistor, Chapter 27.29): The amphisbaena grows twin heads, one in the proper place, and the other where the tail should be. For this reason the snake glides in a circular shape, as the heads, contrary to what is right, strain from both ends. - [Arwen Apps translation, 2011]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 4:20): The amphisbaena is named because it has two heads, one in the proper place and one on the tail, and it advances with both heads leading, its body trailing in a loop. This alone of the snakes trusts itself to the cold, and comes out first of all the serpents. Concerning it Lucan says (Civil War 9.719): Grievous is the amphisbaena, turning toward its two heads. Its eyes glow like lamps.- [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Serpents 8.3): Ansibena is a serpent having two heads, one in its usual place, the other on its tail. This causes the serpent to run in circles with both heads; in his book Solinus calls it amphine. Aristotle reports about the serpents of the East which have two heads; but he says that this happened because of the monstrosity of their birth. But the serpents themselves have two heads and one body. Both heads take fish and pass them into one body; with both heads they also creep into their adversaries. However, Aristotle relates the cause of this monstrosity, that if two spermatozoa join in one womb and no wall separates them, then a monstrous snake will be generated. However, this rarely happens in snakes, since the womb of snakes is very well arranged according to the different offspring. Ansibena, as Pliny says, is the only serpent to commit itself to the cold, appearing first of all, and before the song of the cuckoo. Its eyes shine like fire, as Isidore says. - [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book18.9): Also Serpentes and adders be diverse in disposition, figure, and shape, for some have two heads, as the adder Amphisibena. Of him Isidore speaketh in libro. 12. and sayth, that Amphisibena hath that name, for he hath two heads, one in the one ende, and another in the other ende, and runneth and glideth and wrigleth with wrinkles, corcels, & draughts of the body after either head: and among Serpents, onelye this Serpent putteth out himselfe in cold, and putteth himselfe and goeth before all other. Also lib. 8. cap. 14. Plinius sayth the same, and sayth, that Amphisibena hath a double head, as though one mouth were too little to cast venimme. - [Batman]