Standardized anteroposterior measurements of the cranium and the maxilla represented in the median sagittal plane.Na = nasion; Pr = prosthion; Ba = basion; N-Alv = distance between Alveolar (Alv) plane and nasion; Pr-Alv = distance between prosthion and Alv plane; Alv-Ba = distance between basion and Alv plane; CAP = cranium anterio-posterior length = N-Alv + Alv-Ba. MAP = maxilla anterio-posterior length = Pr-Alv.