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With the aid of a dissecting microscope deciduas were teased apart under phosphate buffered saline (PBS) to expose embryos. The extraembryonic region (as defined in the organogenic image) was severed from the rest of the embryos using either mini-Vannas scissors or fine forceps. The embryonic region then was splited into anterior half and posterior half as depicted in the image. The anterior halves of the embryos were then collected into Trizol.