| extraembryonic mesoderm | Extraembryonic ectoderm cells or tissues which, though derived from the zygote, are not part of the embryo proper and along with the extraembryonic mesoderm form the foetal membranes (e.g., amnion). Synonym: primary mesoderm. (05 Mar 2000) |
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| lateral mesoderm | The peripheral thinned-out portion of intraembryonic mesoderm which is continuous with the extraembryonic mesoderm beyond the margins of the embryonic disk; in it develops the intraembryonic celom. Synonym: lateral mesoderm. (05 Mar 2000) |
| lateral plate mesoderm | The peripheral thinned-out portion of intraembryonic mesoderm which is continuous with the extraembryonic mesoderm beyond the margins of the embryonic disk; in it develops the intraembryonic celom. Synonym: lateral mesoderm. (05 Mar 2000) |