head mesoderm head mesoderm primordium P4 P4 HeadMes hms FBbt:00000127 head mesoderm P3 primordium procephalic mesoderm FBbt:00000127 fly_anatomy.ontology HeadMes Anterior region of mesoderm that forms a vertical plate beside the anterior midgut rudiment (Campos Ortega and Hartenstein, 1997). After its initial ingression during ventral furrow formation, it continues to recruit cells from the surface of the embryo until the end of stage 10 (Campos Ortega and Hartenstein, 1997). It gives rise to the pharyngeal musculature, hemocytes, the corpus cardiacum and the visceral muscle of the esophagus (Campos Ortega and Hartenstein, 1997; de Velasco et al., 2006). HeadMesP3 Drosophila developmental tissue