Fig. 2. Supernumerary EZ-I graft in the cephalic region induces an ectopic mesethmoid. (A) Dorsal schematic view of 5-somite quail and chick embryos showing the dissection of EZ-I from a quail embryo and its transplantation into the lateral anterior mesenchyme of a chick embryo. (B) Ventral view at HH35 of the chondrochranium of an operated embryo. A supernumerary mesethmoid develops within the nasofrontal region perpendicularly to the host nasal capsule, which develops normally. (B') Drawing corresponding to B, with the same colour code as in Fig. 1. (C) Transplantation of a quail EZ-I into the mesenchyme of the presumptive first PA of a recipient chick embryo. (D) Lateral view of a skeletal preparation from a 12-day (HH38) operated embryo. A supernumerary mesethmoid can be seen developing within the maxillary arch under the native Meckel's cartilage. ect, ectethmoid; I and II, endoderm zones I and II; Mc, Meckel's cartilage; mes, mesethmoid; mes^*, supernumerary mesethmoid.