part of part of has potential to develop into simple columnar epithelium embryo endoderm mesoderm primitive streak (...) the blastopore equivalent of chordates (germ ring in fish, marginal zone/blastopore lip in frog and node/primitive streak in chick and mouse) (...) (reference 1); Indeed, the primitive streak has been considered the homologue of the blastopore since the 1870s (reference 2).[well established][VHOG] EHDAA2:0001525 EHDAA:185 EMAPA:16072 FMA:293110 The primitive streak is a structure that forms during the early stages of avian, reptilian and mammalian embryonic development[WP]. the midline ridge of the embryonic epiblast that later develops into mesoderm and endoderm[MP] UBERON:0004341 UMLS:C0033153 VHOG includes a very broad grouping here based on http://www.ncbi.nlm.nih.gov/pubmed/9609826 VHOG:0001202 primitive streak - blastopore - germ ring uberon embryonic tissue presumptive structure