Deficiencies of the ethmoid and embryologically related bones of the anterior cranium have been observed in patients with abnormalities in development or placement of the orbits and eyes, nose, upper lip, mouth, and palate. Although these facial anomalies are commonly associated with holoprosencephaly, they may occur in other syndromes or as isolated cases with normocephaly. Such facial alterations represent the consequences of aberrant migration of tissues into the region normally occupied by the ethmoid bone, beginning early in the sixth week of gestation. The subtle interplay of forces involved in the normal development of the median face appears to be mediated by the ethmoid bone. This interaction may be perceived by dividing the ethmoid bone into three functional components which correspond to and operate in each of the major anatomic planes.