From Da Vinci Vitruvian Man.
The Vitruvian Man is a famous drawing with accompanying notes by Leonardo da Vinci made around the year 1490 in one of his journals. It depicts a naked male figure in two superimposed positions with his arms and legs apart and simultaneously inscribed in a circle and square and represents a cornerstone of Leonardo's attempts to relate man to nature. Symbolised the material existence by the square and spiritual existence by the circle. Thus he attempted to depict the correlation between these two aspects of human existence. He was able to relate a man to the two most supreme figures thus proving universal set of proportions for the human body.
Thus here the image represents the two aspects of human nature, spiritual and physical, a man and the beast in one! Leonardo also included therianthropy in his journals but this was never mentioned to the world as far as i know. This first came out in Harry Potter and the Prisoner of Ascaban. You can see a flash of this image during the scene where snape substitutes lupins lesson.
Full view for details.