The categories of facial cleft (subterms) correspond to Tessier, P (1976) Classification of rare craniofacial clefts, Journal of Maxillofacial Surgery; 4:69-92. There exists a competing classification system by Van der Meulen that divides different types of clefts based on where the development arrest occurs in the embryogenesis. The HPO uses the Tessier classification because it is based on phenotype rather than pathophysiological considerations.