the mule takes the place, as it were, of an anima... the anima is someone to be reckoned with. She is an instinctual force. She is a guide... the mule, which can climb very well, represents the anima who serves him, so to speak, in the form of a laborer.
Jung argues that Cardanus's dream-mule is a degraded anima figure, the entire force of the unconscious conscripted into the service of ego-ambition rather than allowed its full relational and transformative range.
, Dream Interpretation Ancient and Modern: Notes from the Seminar Given in 1936-1941, 2014thesis