Median facio-cerebral anomalies in chick embryos resulting from local destruction of the anteriormost parts of the early neural plate and neural crest.

With the aid of micro-laser irradiation, in a total of 123 chick embryos varying in age from 24-26 hours of incubation (2- to 6-somite stages), the anteriormost parts of the neural crest and the neural plate were eliminated. As a result of this treatment, 15 out of 59 embryos, studied 24 hours after irradiation, showed manifest signs of maldevelopment of the telencephalon, eyes and olfactory placodes. At the age of 7 days (6 days after irradiation), the surviving 25 embryos all proved to have developed median facio-cerebral anomalies. These anomalies included arhinencephaly, holoprosencephaly, anophthalmia, synophthalmia, microphthalmia, absence or reduction of the nasal structures, sometimes combined with the presence of a proboscis, and incidentally occurring facial cleft conditions. The 2 surviving 12 days' embryos studied showed similar facio-cerebral anomalies. These results show that median facio-cerebral deformities may devlop as a result of damage inflicted to the anteriormost parts of the early neural plate and neural crest.