has potential to develop into has potential to develop into anatomical entity simple columnar epithelium 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 NCIT:C28402 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