What is intraembryonic mesoderm?

Some articles on intraembryonic mesoderm, mesoderm:

Bilaminar Blastocyst - Epiblast Cells During Gastrulation - Intraembryonic Mesoderm Development
... This layer of cells becomes know as intraembryonic mesoderm ... After the cells have moved bilaterally from the primitive streak and matured, four divisions of intraembryonic mesoderm are made cardiogenic mesoderm, paraxial mesoderm ...