mesenchyme (n.), mesenchymal (adj.)

https://doi.org/10.1351/goldbook.10942

Meshwork of embryonic connective tissue in the mesoderm, from which are formed the bone, muscular, and connective tissues of the body and also the urogenital system, blood vessels, and lymph vessels.

Source:
PAC, 2016, 88, 713. (Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)) on page 778 [Terms] [Paper]