On the origin of the ciliary ganglion in birds studied by the method of interspecific transplantation of embryonic brain regions between quail and chick.

The development of the ciliary ganglion with reference to the site and cells of origin have been investigated by the method of quail-to-chick transplantation of embryonic fore-, mid-and hindbrain regions, and by the method of transplantation of cranial neural crest from specific brain levels. In chimaerical embryos, quail cells originating from the graft end up in the ciliary ganglion, only when the graft is from the midbrain level of quail embryo donors. In fore- and midbrain grafts the ciliary ganglia of chimaerical embryos are composed of chick cells only. The results indicate that the mesencephalon is the principal site for the precursor cells of the ciliary ganglia and clearly rules out any contribution to the ganglia from either the forebrain or hindbrain levels. In interspecific transplantation of cranial neural crest, quail cells originating from the graft are observed consistently in the ciliary ganglion of the operated side when the grafted neural crest material is derived from the mesencephalon of quail embryo donors. On the basis of the evidence provided, it is concluded that mesencephalon is the principal site and the cranial neural crest of this level the source from which the precursor neurons of the ciliary ganglia are derived.