part of develops from embryonic proventriculus embryonic proventriculus intermediate layer fly_anatomy.ontology Intermediate layer of the proventriculus of the embryo. It corresponds to the invaginated foregut with alveolar cells. It contains imaginal cells at the level of the intermediate layer at the anterior end of the proventriculus. FBbt:00005609 portion of tissue proventriculus intermediate layer primordium anterior ectoderm derivative