part of develops into developing embryonic structure late extended germ band embryo circular intestinal visceral muscle fiber dorsal closure embryo trunk visceral muscle primordium circular trunk visceral muscle primordium trunk visceral mesoderm circular visceral muscle precursor P1 ViMus fly_anatomy.ontology splanchopleura FBbt:00000107 circular visceral mesoderm primordium FBbt:00017015 TVM Primordium of the circular visceral muscle of the trunk. Becomes distinct from the rest of the trunk mesoderm by stage 11 when two distinct layers of trunk mesoderm are apparent, the inner of which is the circular visceral muscle primordium. By stage 12, these cells form a palisade consisting of a dorsal row and a ventral row of tightly packed cells. These cells adhere to the anterior and posterior midgut rudiments as they extend. During dorsal closure they spread out to encircle the midgut.