[Etienne Geoffroy Saint-Hilaire (1772-1844) and anencephaly: Contribution of one naturalist to medical knowledge].

Anencephaly, frequent and severe congenital malformation (around 1% childbirth) is know since highest antiquity, but often confused with acephaly. Its existence during Egyptian Antiquity is demonstrated by observation, by E. Geoffroy Saint-Hilaire, of an anencephalous foetus mummy. The first detailed anatomical observations are those of Morgagni, from 1742 to 1762, that is to E.G.S-H., as naturalist but as a doctor, we owe the crucial progress during the 19th century. As anatomist, by fine and meticulous observation of cranio-spinal skeleton, he shows persistency of all osseous pieces, distorted but preserving all their connexions: this brings him to create a fist nomenclature and a first classification. As embryologist, he establishes the principle of development arrest or delay at a given stage of embryonic life, and he affirms that the type of anomaly depends on her occurring date. Collecting his own observations and those of his predecessors, he describes several clinical characters. Observing amniotic flanges, he elaborates a physiopathological concept, identifies the accidental origin of this malformation, and tries to prove it by teratological experimentation.His works will be continued by his son, Isidore, doctor, who is considered as the Teratology science founder.