Fig. 9.
a In plane embryogenetic movement forming the mouth. Anterior to the left, posterior to the right. Initially the blastodisc is approximately round with an anterior sector already present (partly visible here by its darker contrast). The top left image shows the description in terms of radial and orthoradial lines, and the situation of the presumptive mouth. This anterior sector undergoes a contraction, quite similar to avian gastrulation, by which the sector constricts orthoradially. The bottom plates show the mouth area filmed here on the chicken blastodisc, in time-lapse video-microscopy (Mag. 10X, Video 11)). The bottom left image shows a simple overlap of the plates in Video 5, revealing the actual trajectories of the cells. The bottom right image shows the PIV (Particle Imaging Velocimetry, using NIH software by Wayne Rasband, and Tracker Plugin by Olivier Cardoso and Bérengère Abou) extraction, showing the vector field, with a pattern of contraction oriented towards the mouth sector. So during this phase, the contraction is mainly orthoradial (it follows the ring purse-string). b Continuation of mouth formation when the embryo is no longer 2D. As the embryo flexes, the mouth continues to form by a contraction of the edges which were previously the in-plane boundaries of a sector (Mag. 4X, Video ). As these edges constrict, the presumptive gums start to bulge out. c Pattern generated with an “ear generating contraction”, and a “mouth generating contraction”. The mouth area bends inwardly and two gums form, meanwhile the ear territory constricts and the ear crenel forms a hair-pin (Video 13)