The condition of cynocephaly, having the head of a dog ? or of a jackal? is familiar to anyone who has looked at Egyptian inscriptions. Cynocephalus is a Greek word, literally meaning "dog-head", for a sacred Egyptian baboon with the face of a dog. (The binomial name for the Yellow Baboon is Papio cynocephalus, while Cynocephalus has also been adopted as the genus name for an Asian arboreal gliding mammal also known as a Colugo.)
In the Eastern Orthodox Church, which has not downgraded Saint Christopher, certain icons covertly identify him with the head of a dog. The background to the dog-headed Christopher myth is laid in the reign of the Emperor Diocletian, when a man named Reprebus Rebrebus or Reprobus (the "scoundrel") was captured in combat against tribes to the west of Egypt in Cyrenaica, and was assigned to the numerus Marmaritarum or "Unit of the Marmaritae", which suggests an otherwise-unidentified "Marmaritae" perhaps the same as the Marmaricae berber tribe of Cyrenaica. He was reported to be of enormous size, with the head of a dog instead of a man, apparently characteristic of the Marmaritae.
More on this topic at cryptomundo.