Fig. 13. Antibodies to quail endothelial cells were used to obtain this fluorescent photograph of the hindbrain of a quail embryo (comparable in age to that shown in Figure 5). Rhombomeres are numbered. Note that the blood vessels form with respect to the rhombomere boundaries and show a pattern of organization that resembles the segmentation of the neural tube. This is a transient phenomenon, disappearing within a day as both blood vessels and neural tube continue to develop and proliferate.