Harelip and cleft palate conditions in chick embryos following local destruction of the cephalic neural crest. A preliminary note.

With the aid of micro-laser irradiation, in a total of 156 chick embryos unilaterally (a part of) the cephalic neural crest paralleling the posterior portion of the prosencephalon and mesencephalon, was eliminated. As a result of this treatment, 2 out of 22 embryos, studied 24 hours after irradiation, showed a considerable degree of underdevelopment of the mesenchyme in the homolateral first branchial arch. At the age of 7 days (6 days after irradiation) 11 of the 44 surviving embryos proved to have developed a homolateral harelip condition. In 2 of these embryos, a wide palatal cleft was observed as well. These results demonstrate that facial clefts may develop as a result of a local deficiency of neural crest cells.