Within the depth-psychology corpus, ‘Reptilian’ operates primarily as a neuro-anatomical and evolutionary designation anchored in Paul MacLean’s triune brain model, though its resonances extend into somatic trauma theory, Jungian symbolic imagination, and polyvagal neuroscience. Trauma-oriented clinicians — Ogden, Levine, and van der Kolk — assign the reptilian brain (brainstem and cerebellum) decisive authority over survival reflexes: fight, flight, freeze, feigned death, and autonomic self-regulation. Levine argues with particular force that the neo-cortex’s interference with reptilian-initiated discharge cycles is the proximate cause of human traumatization, a claim that makes the reptilian stratum both the site of pathology and the source of cure. Panksepp situates the reptilian core within a layered neuroanatomical architecture as the elaborator of ‘basic instinctual action plans’ for primitive emotive processes. Ogden develops the clinical utility of MacLean’s model pedagogically, using the triune framework to help clients map dysregulation. Porges, approaching the material from polyvagal theory, draws on reptilian cardiac physiology — bradycardia, absence of RSA — to ground his evolutionary hierarchy of autonomic response. Conspicuously, Jungian and mythological writers treat the reptilian register obliquely, through serpent and saurian symbolism, foregrounding its role as carrier of primordial instinct, ancestral connection, and unconscious depth rather than neuroanatomical substrate. The central tension in the corpus is thus between a somatic-functional reading of the reptilian as survival substrate and a symbolic-archetypal reading as the psyche’s chthonic, pre-human ground.