just as the human body shows a common anatomy over and above all racial differences, so, too, the human psyche possesses a common substratum transcending all differences in culture and consciousness. I have called this substratum the collective unconscious.
Jung establishes the foundational analogy between physical and psychic anatomy, grounding the concept of a universal psychic structure in the parallel of shared bodily form across the species.
, Alchemical Studies, 1967thesis