trunk visceral muscle primordium longitudinal trunk visceral muscle primordium FBbt:00017008 fly_anatomy.ontology CVM P1 LoViMus FBbt:00017008 longitudinal visceral mesoderm primordium FBbt:00000108 This primordium first becomes distinct at around stage 11 as a group of cells at the posterior tip of the trunk visceral mesoderm (the tail end of the germ-band). During germ-band retraction these cells migrate anteriorly and split into two clusters - one on either side of the posterior midgut primordium. When these cell reach the anterior tip of the posterior midgut primordium they disperse anteriorly as two rows along the germband. Finally, during midgut closure these cells spread regularly over the underlying circular visceral muscle primordium. longitudinal visceral muscle precursor caudal visceral mesoderm