part of develops from ends during starts during ectoderm stomodeal-hypophyseal primordium An anterior thickening of the sensorial layer of ectoderm, just above the cement gland. The hypophyseal layer separates from the stomodeal layer at NF stage 29 and 30, and when contacted by a protrusion of the foregut, the stomodeal layer will rupture to form the mouth opening at NF stage 39 and 40. XAO:0000032 xenopus_anatomy sensorial layer of neurectoderm primordium NF stage 18 NF stage 40