part of has part develops from develops into dorsal vessel primordium Primordium that makes the inner, contractile layer of the embryonic/larval dorsal vessel. This primordium originates in the mesodermal crest on each side of the embryo. Its component cells (embryonic cardioblasts) become distinct by stage 14. The dorsal vessel is formed by fusion of left and right primordia during, and immediately following, dorsal closure. FBbt:00001665 dorsal vessel specific anlage fly_anatomy.ontology developing embryonic structure dorsal closure embryo circulatory system primordium cardiogenic mesoderm embryonic dorsal vessel embryonic cardioblast trunk mesoderm derivative