While Merleau-Ponty’s Phenomenology of Perception relies on the descriptive register of the body proper, his Sorbonne lectures on child psychology investigate the genesis of the experience of a body as one’s own. I demonstrate the uniqueness of Merleau-Ponty’s account of the narcissistic affect and sociality involved in this developmental process, distinguishing his account vis-à-vis Wallon’s and Lacan’s studies of the mirror stage. I conclude that in Merleau-Ponty’s account, (1) the experience of the body proper is not singular, but encompasses a range of phenomenological variation; and (2) the genesis of the body proper is not confined to the mirror stage. The production of bodily boundaries is an ongoing process identified not only with its advent in childhood, but also with adult emotional life. The boundaries between inner and outer domains of perception are not merely discovered, but must be negotiated and cultivated in the intercorporeal affective dramas of adult life.