| coelom | <biology, embryology> An internal fluid-filled body cavity (other than the gut) within an organism, it lies between the gut (derived from the endoderm) and the outer body wall (derived from the ectoderm) and is lined entirely with tissue derived from the mesoderm. It is formed from the mesoderm during embryonic development. It is found in triploblastic animals called coelomates. (09 Oct 1997) |
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| intraembryonic | Within the embryonic body, e.g., the portion of the umbilical vein within the embryo (in contrast to the portion in the umbilical cord which is discarded at birth). Compare: extraembryonic. (05 Mar 2000) |
| intraembryonic mesoderm | Mesoderm derived from the primitive streak and lying between the ectoderm and endoderm. Synonym: secondary mesoderm. (05 Mar 2000) |