In Jungian psychology, the animus can be identified as the totality of the unconscious masculine psychological qualities that a female possesses. It is an archetype of the collective unconscious and not an aggregate of father, brothers, uncles, or teachers, though these aspects of the personal unconscious can influence for good or ill the person. Jung postulated that women have a host of animus images,[15] with each stage of a woman's animus development being represented by a different image.
Adam and the cowboy represent two animus figures for Diane, but I'm not sure at this point whether each man represents a different stage of Diane's animus development, or if the two images exist concurrently and that therefore Diane has some kind of 'split animus', so to speak. The cowboy represents the more masculine of the two images, and he also represents that part of the animus that serves as mediator between Diane's unconscious and conscious mind. Adam is the more 'intellectual' of the pair of men, and he also represents the part of Diane's animus that has been cross-contaminated with unconscious contents from her shadow, the shadow being associated with repressed weaknesses and repressed primitive instincts: recall Adam beating up the Castigliane brothers' car with a golf club. (The fact that Adam is mostly shown wearing dark clothing throughout the movie, is one hint to us from Lynch that Adam is tied in with the shadow.)
Jung believed that over-awareness of the animus could provide a premature conclusion to the individuation process - "a kind of psychological short-circuit, to identify the animus at least provisionally with wholeness".[a] Instead of being "content with an intermediate position", the animus seeks to usurp "the self, with which the patient's animus identifies. This identification is a regular occurrence when the shadow, the dark side, has not been sufficiently realized".[b]
a. C. G. Jung, Alchemical Studies (London 1978) p. 268
b. Jung, Alchemical p. 268
