Developmental anomalies of the lower face and the hyoid cartilage due to partial elimination of the posterior mesencephalic and anterior rhombencephalic neural crest in chick embryos.

In an effort to verify the supposition that a normal development of the lower face and the hyoid apparatus is dependent on the availability of a sufficient number of cells derived from the posterior mesencephalic and anterior rhombencephalic parts of the neural crest, in a total of 52 six-somite stage chick embryos (about 26 hours of incubation) these parts of the neural crest were partially eliminated by tangential micro-laser irradiation. Among the 17 irradiated embryos sacrificed after 24 hours, several ones showed an underdevelopment of the mesenchyme in the ventral part of the first branchial arch; in 2 of these cases, additionally the second branchial arch was underdeveloped. At the age of 7-8 days, 4 out of 15 surviving embryos showed an underdevelopment of the lower beak and a reduction in size of Meckel's cartilage; in 3 of these cases, in addition, a median cleft in the lower beak and/or reduction or absence of the hyoid cartilage were observed. From these observations the conclusion is drawn that for a normal development and growth of the mandibular part of the face and the hyoid cartilage sufficient numbers of posterior mesencephalic and anterior rhombencephalic neural crest cells are indispensable, indeed.