Developmental deficiencies of the upper facial skeleton due to partial elimination of mesencephalic neural crest cells in the chick embryo.

: With the aim to test the hypothesis that cells derived from the mesencephalic portion of the neural crest, are involved in the process of differentiation of various upper facial bones, in 41 chick embryos of the 6-somite stage (approx. 26 hours of incubation) the anterior and middle thirds of this part of the neural crest were partially eliminated by micro-laser irradiation, either unilaterally or bilaterally. Of the 14 embryos sacrificed at the age of 12 days, a number of 6 proved to have developed harelip and/or cleft palate conditions. In these embryos, in addition a reduction or absence of the maxillary, palatal, jugale and quadrato-jugale was observed. On the contrary, other facial bones as well as the first and second branchial arch cartilages proved to have developed normally. From these results the conclusion may be drawn that (a sufficient number of) cells from the anterior and middle thirds of the mesencephalic neural crest are indispensable for a normal differentiation of the maxillary, palatal, jugale and quadrato-jugale.