Figure 3

Typical PIV calculation of the displacement field for a force applied along the midline. In this example, we applied a force F = 190 nN in the caudal direction at the AP position of the last-formed somite pair (large arrow). Small arrows represent the local average displacements for square subregions of the embryo. The displacement scale is magnified compared to the image scale; the displacements in the center are on the order of 5 μm. The actual data set is a lattice of 40 by 32 displacement vectors; for clarity only a 20 by 16 sublattice is displayed. The images are 640 by 512 pixels.