Fig. 3

The flow chart and illustrations of our method to obtain the standard chick embryonic brain slices corresponding to the atlas in vivo. The amplificatory illustrations are shown in the bottom for clearly showing the positioning method. a, b and c are three orthotropic planes of the egg after first positioning scan; d and e are two serial slices in the plane with the largest area of two eyes’ projection. One set of positioning lines (blue) is adjusted to pass through the two eyeballs (green circle) and the corresponding orthotropic set of positioning lines (yellow) is put to pass through the beak; f, g and h are three serial slices in the plane with the second largest area of two eyes’ projection. Another set of positioning lines (red) should also be adjusted to pass through two eyeballs (green circle); i, j and k are three orthotropic planes of chick embryonic brain after second positioning scan; l, m and n show the positioning method to get the standard sagittal planes of brain with the positioning lines passing through the mid-line of the brain; o is the mid-sagittal plane with positioning lines corresponding to the section direction of atlas in p. The positioning lines to get coronal slices are perpendicular to the line which is tangent to the dorsal surface of parietal and frontal bones (red line in o and p). q is one of the standard coronal slices and r is corresponding established atlas [20]