part of part of transformation of prechordal plate A horseshoe-shaped thickening of the endoderm at the cranial (rostral) end of the primitive streak formed by the involution of Spemann's organizer cells which, together with the notochord, induces the formation of the neural plate from the overlying ectodermal cells and contributes mesodermal type cells to the surrounding tissue AAO:0011085 Axial hypoblast located anterior to the chorda mesoderm; the polster is its most anterior region. Kimmel et al, 1995.[TAO] Axial mesoderm that lies anterior to the notochord and that underlies the forebrain. [Amphioxus_goosecoid_and_the_evolution_of_the_head_organizer_and_prechordal_plate._Evolution_and_Development_(2008)_2(6):303-310, Neidert_AH, Panopoulou_G_and_Langeland_JA][VHOG] EHDAA2:0001493 EHDAA:181 FMA:295532 TAO:0000060 TODO - check; developmental relationship to anterior hypoblast in ZFA? There are two opposing models that can potentially explain the differences in gsc (goosecoid) expression between amphioxus and vertebrates. In one model, the vertebrate gsc expression pattern more closely resembles the common ancestral state and the amphioxus gsc expression pattern is a derivation associated with its unique morphology. (...) In an alternate model, the amphioxus gsc expression pattern most closely represents the common ancestral state and the vertebrate pattern is derived. This model suggests that the evolution of vertebrates was accompanied by the segregation of gsc expression, from a more general domain underlying the entire brain anlage to a distinct forebrain organizer domain and subsequent prechordal plate. We feel this second model is more parsimonious than the first model in that what would be novel anterior gsc expression in vertebrates directly correlates with a novel vertebrate anterior structure, the prechordal plate.[well established][VHOG] UBERON:0003063 UBERON:0004881 VHOG:0000086 XAO:0000079 ZFA:0000060 head mesenchyme head mesoderm uberon axial mesoderm developing anatomical structure prechordal mesoderm