I think the doghearted bit might stem from the belief in the existance of a race called the 'Dogheads'.
During medieval times church elders would go on pilgrimages to the edges of the earth, literally because they thought is was flat back then, and bring back tales of a race of beings who had human bodies and the heads of dogs. Nobody doubted men of such reverance but they were obviously talking total bulls**t for reasons unknown. There was furious debate on whether the dogheads should be classed as citizens but it was decided that as they wore clothes that they had a sense of shame and therefore were cool to stay.
Medieval folklore is really something else, even worse than my digressions from the point.