Differential growth and tissue shifts in the developing neck of the chick embryo. An experimental study

The differential growth of the neck was studied by means of linear marks in the chick embryo. The marks were inserted into 3 different zones: Zone I, between the level of 1st and 2nd branchial cleft, zone II, between the level of the 2nd and 3rd branchial cleft, and zone III, between the level of the 3rd branchial cleft and the Cuvier duct. The deformation and dispersion of marks after further incubation of labelled embryos indicate: 1. A caudocranially oriented growth of axial and paraaxial structures causing the displacement of branchial to axial and paraxial structures, 2. an extent growth in the region of the 3rd branchial arch in contrast to other branchial arches with 2 exceptions: the extent craniocaudal growth of the operculum (2nd branchial arch) and the extent caudocranially oriented growth of the hypobranchial region. On the base of our findings the differences in the topography of some neck organs of birds and mammals could be explained.