A child with a lateral trunk replacing one side of the external nose is presented with a detailed X-ray study of the deformed head. In the explanation of the etiology and teratogenesis of this facial anomaly, the modern embryologic development of the head is reviewed and correlated with the findings of this anomaly. It is felt that the lesion responsible for a proboscis lateralis involves the organizer tissue for the naso-face. As a secondary phenomenon, the development of the maxillary process is retarded and a spectrum of defects, common to many mid-face derangements, is identified and explained.